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the anticipated amount, timing and accounting of revenues; contingent, milestone, royalty and other payments under licensing, collaboration or acquisition agreements; tax positions and contingencies; collectability of receivables; pre-approval inventory; cost of sales; research and development costs; compensation and other selling, general and administrative expenses; amortization of intangible assets; foreign currency exchange risk; estimated fair value of assets and liabilities; and impairment assessments;

•	expectations, plans and prospects relating to sales, pricing, growth and launch of our marketed and pipeline products;

•	the timing, outcome and impact of administrative, regulatory, legal and other proceedings related to our patents and other proprietary and intellectual property rights, tax audits, assessments and settlements, pricing matters, sales and promotional practices, product liability and other matters;

•	patent terms, patent term extensions, patent office actions and expected availability and period of regulatory exclusivity;

•	the potential impact of increased product competition in the markets in which we compete, including increased competition from generics, biosimilars, prodrugs and other products approved under alternative regulatory pathways;

•	our plans and investments in our core and emerging growth areas, as well as implementation of our 2017 corporate strategy;

•	the drivers for growing our business, including our plans and intent to commit resources relating to research and development programs and business development opportunities;

•	our ability to finance our operations and business initiatives and obtain funding for such activities;

•	the costs and timing of potential clinical trials, filings and approvals, and the potential therapeutic scope of the development and commercialization of our and our collaborators’ pipeline products;

•	adverse safety events involving our marketed products or generic or biosimilar products marketed by others;

•	the potential impact of healthcare reform in the United States (U.S.) and measures being taken worldwide designed to reduce healthcare costs and limit the overall level of government expenditures, including the impact of pricing actions and reduced reimbursement for our products;

•	our manufacturing capacity, use of third-party contract manufacturing organizations and plans and timing relating to the expansion of our manufacturing capabilities, including anticipated investments and activities in new manufacturing facilities;

•	the anticipated benefits and the potential costs and expenses related to our current or future initiatives to streamline our operations and reallocate resources;

•	the impact of the continued uncertainty of the credit and economic conditions in certain countries in Europe and our collection of accounts receivable in such countries;

•	the potential impact on our results of operations and liquidity of the United Kingdom's (U.K.) intent to voluntarily depart from the European Union (E.U.);

•	lease commitments, purchase obligations and the timing and satisfaction of other contractual obligations;

•	the impact of new laws, regulatory requirements, judicial decisions and accounting standards; and

•	the anticipated costs and tax treatment of the spin-off of our hemophilia business as well as the timeline for selling substantially all remaining hemophilia related inventory.

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•	“Biogen,” the “company,” “we,” “us” and “our” refer to Biogen Inc. and its consolidated subsidiaries;

•	“RITUXAN” refers to both RITUXAN (the trade name for rituximab in the U.S., Canada and Japan) and MabThera (the trade name for rituximab outside the U.S., Canada and Japan); and

•	"ELOCTATE" refers to both ELOCTATE (the trade name for Antihemophilic Factor (recombinant), Fc Fusion Protein in the U.S., Canada and Japan) and ELOCTA (the trade name for Antihemophilic Factor (recombinant), Fc Fusion Protein in the E.U.).

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•	In April 2018 we presented new real-world data that demonstrated that people with RMS treated with TECFIDERA early in the course of their disease may experience better long-term outcomes. These data were presented at the 70th annual meeting of the American Academy of Neurology (AAN) in Los Angeles, CA.

•	In October 2018 we presented clinical and real-world evidence that further support the long-term efficacy and well characterized safety of TECFIDERA early within the disease course. These data were presented at the 34th Congress of the European Committee for Treatment and Research in MS (ECTRIMS) in Berlin, Germany.

•	In April 2018, at the 70th annual meeting of the AAN in Los Angeles, CA, we presented new real-world data that demonstrated that people with RMS treated with TYSABRI early in the course of their disease may experience better long-term outcomes.

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In April 2018 we presented observational data that demonstrated that extended interval dosing with TYSABRI is associated with a significant reduction in the risk of progressive multifocal leukoencephalopathy (PML), a serious brain injury, compared with standard interval dosing in the TOUCH prescribing program. These data were presented at the 70th annual meeting of the AAN in Los Angeles, CA. In November 2018 we initiated the Phase 3b NOVA study evaluating the efficacy and safety of extended interval dosing (every six weeks) for natalizumab compared to standard interval dosing in patients with RMS and enrolled the first patient in December 2018.

•	In October 2018 we presented clinical and real-world evidence that further support the long-term efficacy and well characterized safety of TYSABRI early within the disease course. These data were presented at the 34th Congress of ECTRIMS in Berlin, Germany.

•	In December 2018 we dosed the first patient in a bioequivalence study to test whether exposure levels of PLEGRIDY are maintained with intramuscular administration.

•	In March 2018 we and AbbVie announced the voluntary worldwide withdrawal of ZINBRYTA for RMS.

•	In April 2018 MRI and relapse results from the Phase 3 EVOLVE-MS-1 study for diroximel fumarate in patients with relapsing remitting MS (RRMS) were presented at the 70th annual meeting of the AAN in Los Angeles, CA.

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In December 2018 Alkermes Pharma Ireland Limited, a subsidiary of Alkermes plc (Alkermes), submitted a New Drug Application (NDA) to the U.S. Food and Drug Administration (FDA) for diroximel fumarate. Alkermes is seeking approval of diroximel fumarate under the 505(b)(2) regulatory pathway. If approved, we intend to market diroximel fumarate under the brand name VUMERITY. This name has been conditionally accepted by the FDA and will be confirmed upon approval.

•	In September 2018 we completed enrollment of the Phase 2b AFFINITY study, evaluating opicinumab as an add-on therapy in MS patients who are adequately controlled on their anti-inflammatory disease-modifying therapy (DMT), versus the DMT alone.

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In February 2018 the end of study results from CHERISH, the Phase 3 study evaluating SPINRAZA for the treatment of individuals with later-onset SMA, were published in The New England Journal of Medicine. Results from CHERISH demonstrated meaningful motor function and upper limb improvements in individuals with later-onset SMA rarely seen in the natural course of the disease, which is typically a continued decline in motor function over time.

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In March 2018 we presented new interim Phase 2 results from NURTURE, the ongoing open-label, single-arm study evaluating the efficacy and safety of SPINRAZA among pre-symptomatic infants with SMA. In NURTURE, all infants treated with SPINRAZA were alive, did not require permanent ventilation and showed improvement in motor function and motor milestone achievements as of July 5, 2017, compared to the disease's natural history. We also presented a case series demonstrating SPINRAZA's effectiveness among teens and young adults. These data were presented at the Muscular Dystrophy Association Clinical Conference in Arlington, VA.

•	In April 2018 we presented data from the CS2/CS12 studies that demonstrated that with SPINRAZA treatment, older patients were able to walk longer distances while experiencing stable or less fatigue at the same time, in contrast to natural history. The study participants have Type 2 or Type 3 SMA and were ages 12 to 15 years at study enrollment.

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In June 2018 we presented data from our SPINRAZA clinical development program for SMA at the Cure SMA 2018 Annual SMA Conference in Dallas, TX. Platform and poster presentations highlighted interim analyses from the SHINE and NURTURE studies, which assess SPINRAZA's safety and efficacy among those with infantile-onset SMA, and data on the utility of plasma phosphorylated neurofilament heavy chain (pNF-H) as a potential biomarker for SMA.

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In October 2018 we presented new interim results from NURTURE, an ongoing open-label, single-arm efficacy and safety study of SPINRAZA in 25 presymptomatic infants with SMA at the Annual Congress of the World Muscle Society held in Mendoza, Argentina. As of May 2018 all NURTURE study participants were alive and none required permanent ventilation, in contrast to the natural history of SMA. In addition, 100% of study participants achieved the motor milestone of sitting independently, 88% were able to walk with assistance and 77% were able to walk independently. All NURTURE study participants were older than 15 months at the time of the analysis.

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In November 2018 we were awarded the 2018 International Prix Galien as Best Biotechnology Product for SPINRAZA. The prestigious honor marks the seventh Prix Galien for SPINRAZA, following country recognitions in the U.S., Germany, Italy, Belgium-Luxembourg, the Netherlands, and the U.K. The International Prix Galien is given every two years by Prix Galien International Committee members in recognition of excellence in scientific innovation to improve human health.

•	In May 2018 we submitted an Investigational New Drug Application for BIIB089 in SMA.

•	In October 2018 we announced that the FDA had placed BIIB089 on a clinical hold.

•	In September 2018 we enrolled the first patient in the Phase 1 study evaluating BIIB078, an ASO drug candidate, in adults with C9ORF72-associated ALS.

•	In December 2018 we and Ionis announced results from a positive interim analysis of the ongoing Phase 1 study of BIIB067 in ALS with SOD1 mutations. The interim analysis showed that, over a three month period,

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•	In February 2018 we announced that, following a pre-planned blinded sample size review of the data per study protocol and based on variability in the primary endpoint that was greater than study protocol assumed, we increased the sample size of ENGAGE and EMERGE, the Phase 3 studies of aducanumab.

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In March 2018 we presented data from the long-term extension (LTE) of the Phase 1b PRIME study of aducanumab at the Advances in Alzheimer's and Parkinson's Therapies (AAT-AD/PD) Focus Meeting in Torino, Italy. The data presentation included the Centiloid scale, a method used to standardize the aducanumab Phase 1b PRIME study amyloid-PET (positron emission tomography) results as previously measured by the composite Standardized Uptake Value Ratio.

•	In April 2018 we presented 36-month data and 24-month titration data from the Phase 1b PRIME study of aducanumab at the 70th annual meeting of the AAN in Los Angeles, CA.

•	In July 2018 we completed enrollment of ENGAGE and EMERGE, the Phase 3 studies of aducanumab.

•	In July 2018 we presented a new analysis from the Phase 1b PRIME study of aducanumab at the Alzheimer's Association International Conference (AAIC) 2018 in Chicago, IL. These data included a poster presentation on the 24-month analysis of APOE ε4 carriers in the Phase 1b PRIME study and a platform presentation on the 24-month clinical dementia rating scale analysis of the Phase 1b PRIME study.

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In August 2018 we and our collaboration partner Eisai Co., Ltd. (Eisai) announced results from a recent analysis of the ongoing LTE of the Phase 1b PRIME study of aducanumab. The updated analyses include data from the placebo-controlled period and LTE for patients treated with aducanumab up to 36 months in the titration cohort and up to 48 months in the fixed dose cohorts. The results are generally consistent with previous interim analyses, and there were no changes to the risk-benefit profile of aducanumab.

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In October 2018 we presented data on the efficacy of aducanumab and the cumulative safety data from the LTE of the Phase 1b PRIME study of patients with prodromal and mild Alzheimer's disease. These data were presented at the Clinical Trials on Alzheimer's Disease (CTAD) annual meeting in Barcelona, Spain. These results are generally consistent with previous interim analyses, and there were no changes to the risk-benefit profile of aducanumab.

•	In November 2018 we initiated a Phase 2 study of aducanumab to assess the clinical relevance of asymptomatic amyloid related imaging abnormalities (ARIA). This Phase 2 study was not required by regulators and is not necessary for registration.

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In December 2017 we and our collaboration partner Eisai announced that the Phase 2 study of BAN2401, a monoclonal antibody that targets amyloid beta aggregates, an Eisai product candidate for the treatment of AD, did not meet the criteria for success based on a Bayesian analysis at 12 months as the primary endpoint in an 856-patient Phase 2 clinical study, an endpoint that was designed to enable a potentially more rapid entry into Phase 3 development. In July 2018, based upon the final analysis of the data at 18 months, we and Eisai announced that the topline results from the Phase 2 study demonstrated a statistically significant slowing in clinical decline and reduction of amyloid beta accumulated in the brain. The study achieved statistical significance on key predefined endpoints evaluating efficacy at 18 months on slowing progression in Alzheimer’s Disease Composite Score (ADCOMS) and on reduction of amyloid accumulated in the brain as measured using amyloid-PET. In July 2018 Eisai presented this data in an oral session at AAIC 2018 in Chicago, IL.

•	In October 2018 our collaboration partner Eisai presented clinical and biomarker updates from the Phase 2 study of BAN2401 at the CTAD annual meeting in Barcelona, Spain.

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In June 2018 we and our collaboration partner Eisai announced that elenbecestat, the oral BACE (beta amyloid cleaving enzyme) inhibitor, demonstrated an acceptable safety and tolerability profile in the Phase 2 study, and the results demonstrated a statistically significant difference in amyloid-beta levels in the brain measured by amyloid-PET. A numerical slowing of decline in functional clinical scales of a potentially clinically important difference was also observed, although this effect was not statistically significant. In July 2018 the data were featured in an Eisai poster presentation at AAIC 2018 in Chicago, IL.

•	In October 2018 our collaboration partner Eisai presented safety and efficacy data for elenbecestat from the Phase 2 study in mild cognitive impairment-to-moderate AD at the CTAD annual meeting in Barcelona, Spain.

•	In May 2018 we initiated a Phase 2 study of BIIB092 for AD.

•	In January 2018 we dosed the first patient in the Phase 2 SPARK study of BIIB054 in Parkinson's disease.

•	In April 2018 we presented Phase 1 study results for BIIB054 in Parkinson's disease at the 70th annual meeting of the AAN in Los Angeles, CA.

•	In October 2018 we presented an overview of the design of the Phase 2 SPARK study of BIIB054 in Parkinson's disease at the International Congress of Parkinson's Disease and Movement Disorders in Hong Kong.

•	In March 2018 we presented data regarding details about the design of the ongoing Phase 2 PASSPORT study of BIIB092 for PSP at the AAT-AD/PD Focus Meeting in Torino, Italy.

•	In April 2018 we presented Phase 1 study results of BIIB092 for PSP as well as details about the design of the ongoing Phase 2 PASSPORT study of BIIB092 for PSP at the 70th annual meeting of the AAN in Los Angeles, CA.

•	In September 2018 we completed enrollment of the Phase 2 PASSPORT study of BIIB092 for PSP.

•	In October 2018 the FDA granted BIIB092 fast track designation for PSP.

•	In October 2018 we presented safety data from the Phase 1 LTE study of BIIB092 for PSP and baseline demographics from the Phase 2 PASSPORT study of BIIB092 for PSP at the International Congress of Parkinson's Disease and Movement Disorders in Hong Kong.

•	In September 2018 we enrolled the first patient in the Phase 3 CHARM study of BIIB093 in large hemispheric infarction (LHI), a severe form of ischemic stroke.

•	In March 2018 we dosed the first patient in the Phase 2 OPUS study of natalizumab in drug-resistant focal epilepsy.

•	In December 2018 we dosed the first patient in our Phase 2b study of BIIB104 in CIAS.

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•	In May 2018 we initiated a Phase 2 study of BIIB074 in small fiber neuropathy (SFN).

•	In March 2018 we initiated a Phase 1 study of BIIB095, a Nav 1.7 inhibitor for neuropathic pain.

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In June 2018 we and Samsung Bioepis announced pooled analysis results from three separate Phase 3 studies comparing the efficacy and safety of BENEPALI in reference to etanercept, FLIXABI in reference to infliximab and IMRALDI in reference to adalimumab in patients with moderate to severe rheumatoid arthritis. The data indicated that the incidence of anti-drug antibodies was comparable between the biosimilars and their reference products and that radiographic progression of disease was minimal and comparable across all treatment groups. The data were presented at the Annual European Congress of Rheumatology (EULAR 2018) in Amsterdam, Netherlands.

•	In October 2018 we and Samsung Bioepis launched IMRALDI, an adalimumab biosimilar referencing HUMIRA, in Europe.

•	In January 2018 the European Commission (EC) granted a marketing authorization for OCREVUS for the treatment of RMS and PPMS.

•	In June 2018 the FDA approved RITUXAN for the treatment of adult patients with moderate to severe pemphigus vulgaris. Subsequently, the FDA confirmed orphan-drug exclusivity associated with this approval.

•	In September 2018 we dosed the first patient in the Phase 2b study of BG00011 in idiopathic pulmonary fibrosis (IPF), a chronic irreversible and ultimately fatal disease characterized by a progressive decline in lung function.

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In October 2018 we and our collaboration partner UCB announced top-line results from the Phase 2b study evaluating the safety and efficacy of dapirolizumab pegol (DZP), an anti-CD40L pegylated Fab, in adults with moderately-to-severely active systemic lupus erythematosus (SLE) despite receiving standard-of-care treatment such as corticosteroids, anti-malarials and non-biological immunosuppressants. The primary endpoint of the study, which was to demonstrate a dose response at 24 weeks on the British Isles Lupus Assessment Group (BILAG)-based Composite Lupus Assessment (BICLA), was not met (p=0.06). The study did demonstrate consistent and potentially meaningful improvements for the majority of clinical endpoints in patients treated with DZP compared with placebo. In addition, biomarker data demonstrated evidence of proof of biology and DZP demonstrated an acceptable safety profile.

•	In February 2018 we announced that the Phase 2b dose-ranging ACTION study investigating natalizumab in individuals with acute ischemic stroke (AIS) did not meet its primary endpoint. Based on these results, we have discontinued development of natalizumab in AIS. The results of the Phase 2b ACTION study do not impact the benefit-risk profile of natalizumab in approved indications, including MS.

•	In October 2018 we announced that we completed the Phase 2b study of vixotrigine (BIIB074) for the treatment of painful lumbosacral radiculopathy (PLSR). The study did not meet its primary or secondary

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In December 2018 we notified Applied Genetic Technologies Corporation (AGTC) of the termination of our collaboration agreement with AGTC. The termination of this collaboration agreement will be effective in March 2019. As a result, we will have no further involvement in the development of BIIB087, an investigational adeno-associated virus (AAV)-based gene therapy for the treatment of X-linked Retinoschisis (XLRS), BIIB088, an investigational AAV-based gene therapy for the treatment of X-linked Retinitis Pigmentosa (XLRP), and early stage discovery programs in two ophthalmic diseases and one non-ophthalmic condition.

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In December 2018 we notified the University of Pennsylvania (UPenn) that we will be terminating certain programs under our collaboration and alliance with UPenn, including the development of therapeutic approaches that target the eye, skeletal muscle and central nervous system and research and validation of next generation gene transfer technology using AAV gene delivery vectors and exploring the expanded use of genome editing technology as a potential therapeutic platform. The termination of these programs will be effective in May 2019. This termination did not impact our collaboration with UPenn for the development of BIIB089 for the treatment of SMA.

(1)	Interferon includes product revenues from AVONEX and PLEGRIDY.

(2)	For 2018, 2017 and 2016 other includes product revenues from FAMPYRA, FUMADERM, BENEPALI, FLIXABI and ZINBRYTA. For 2018 other also includes product revenues from IMRALDI, which was launched in Europe in October 2018. For 2017

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(3)	Anti-CD20 therapeutic programs includes revenues from RITUXAN, RITUXAN HYCELA, GAZYVA and OCREVUS.

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(1)	In addition to patent protection, certain of our products are entitled to regulatory exclusivity in the U.S. and the E.U. expected until the dates set forth below:

(2)	This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2024.

(3)	This patent was revoked in a European opposition. This decision is being appealed. This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2029.

(4)	This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2028.

(5)	Reflects SPCs granted in most European countries and pediatric extension in some countries.

(6)	This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2026.

(7)	This patent was revoked in a European opposition. This decision is being appealed. This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2026.

(8)	This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2031.

(9)	This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2031.

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•	safety or efficacy issues;

•	the introduction or greater acceptance of competing products, including lower-priced competing products;

•	limitations and additional pressures on product pricing or price increases, including those resulting from governmental or regulatory requirements, increased competition or changes in, or implementation of, reimbursement policies and practices of payors and other third parties; or

•	adverse legal, administrative, regulatory or legislative developments.

•	our limited marketing experience within certain SMA markets, which may impact our ability to develop additional relationships with the associated medical and scientific community;

•	the lack of readiness of healthcare providers to treat patients with SMA;

•	the effectiveness of our commercial strategy for marketing SPINRAZA;

•	our ability to maintain a positive reputation among patients, healthcare providers and others in the SMA community, which may be impacted by pricing and reimbursement decisions relating to SPINRAZA; and

•	the introduction of other products in development that, if successfully developed and approved, may compete with SPINRAZA in the SMA market, including potential gene therapy or oral products.

•	changes in, and implementation of, federal, state or foreign government regulations or private third-party payors’ reimbursement policies;

•	pressure by employers on private health insurance plans to reduce costs;

•	consolidation and increasing assertiveness of payors, including managed care organizations, health insurers, pharmacy benefit managers, government health administration authorities, private health insurers and other organizations, seeking price discounts or rebates in connection with the placement of our

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•	our value-based contracting pilot program pursuant to which we aim to tie the pricing of our products to their clinical values by either aligning price to patient outcomes or adjusting price for patients who discontinue therapy for any reason, including efficacy or tolerability concerns.

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•	the introduction of more efficacious, safer, less expensive or more convenient alternatives to our MS products, including our own products and products of our collaborators;

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the introduction of biosimilars, follow-on products, generic versions of branded MS products, prodrugs or products approved under other alternative regulatory pathways, which would be significantly less costly than our products to bring to market and would be offered for sale at lower prices, and could result in a significant percentage of the sales of our products being lost to such biosimilars, follow-on products, generic versions of branded MS products, prodrugs or products approved under other alternative regulatory pathways;

•	the off-label use by physicians of therapies indicated for other conditions to treat MS patients;

•	patient dynamics, including the size of the patient population and our ability to attract and maintain new and current patients to our therapies;

•	damage to physician and patient confidence in any of our MS products or generic or biosimilars of our MS products, or to our sales and reputation as a result of label changes or adverse experiences or events that may occur with patients treated with our MS products or generic or biosimilars of our MS products;

•	inability to obtain appropriate pricing and reimbursement for our MS products compared to our competitors in key international markets; or

•	our ability to obtain and maintain patent, data or market exclusivity for our MS products.

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•	we may be unable to control the resources our collaborators or third parties devote to our programs, products or product candidates;

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disputes may arise under an agreement, including with respect to the achievement and payment of milestones or ownership of rights to technology developed with our collaborators or other third parties, and the underlying agreement with our collaborators or other third parties may fail to provide us with significant protection or may fail to be effectively enforced if the collaborators or third parties fail to perform;

•	the interests of our collaborators or third parties may not always be aligned with our interests, and such parties may not pursue regulatory approvals or market a product in the same manner or to the same extent that we would, which could adversely affect our revenues;

•	third-party relationships and collaborations often require the parties to cooperate, and failure to do so effectively could adversely affect product sales, or the clinical development or regulatory approvals of products under joint control, could result in termination of the research, development or commercialization of product candidates or could result in litigation or arbitration;

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any failure on the part of our collaborators or other third parties to comply with applicable laws and regulatory requirements in the marketing, sale and maintenance of the marketing authorization of our products or to fulfill any responsibilities our collaborators or other third parties may have to protect and enforce any intellectual property rights underlying our products could have an adverse effect on our revenues as well as involve us in possible legal proceedings; and

•	any improper conduct or actions on the part of our collaborators or other third parties could subject us to civil or criminal investigations and monetary and injunctive penalties, and could adversely impact our ability to conduct business, our operating results and our reputation.

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new laws, regulations or judicial decisions, or new interpretations of existing laws, regulations or judicial decisions, related to health care availability, pricing or marketing practices, compliance with wage and hour laws and other employment practices, method of delivery, payment for health care products and services, compliance with health information and data privacy and security laws and regulations, tracking and reporting payments and other transfers of value made to physicians and teaching hospitals, extensive anti-bribery and anti-corruption prohibitions, product serialization and labeling requirements and used product take-back requirements;

•	changes in the FDA and foreign regulatory approval processes that may delay or prevent the approval of new products and result in lost market opportunity;

•	U.S. government shutdowns, similar to the one that began in December 2018, may result in delays to the FDA's review and approval process, slowing the time necessary for new drug candidates to be reviewed and/or approved, which may adversely affect our business;

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requirements that provide for increased transparency of clinical trial results and quality data, such as the EMA’s clinical transparency policy, which could impact our ability to protect trade secrets and competitively-sensitive information contained in approval applications or could be misinterpreted leading to reputational damage, misperception or legal action, which could harm our business; and

•	changes in FDA and foreign regulations that may require additional safety monitoring, labeling changes, restrictions on product distribution or use or other measures after the introduction of our products to market, which could increase our costs of doing business, adversely affect the future permitted uses of approved products or otherwise adversely affect the market for our products.

•	the inability to obtain necessary foreign regulatory or pricing approvals of products in a timely manner;

•	uncertainties regarding the collectability of accounts receivable;

•	fluctuations in foreign currency exchange rates that may adversely impact our revenues, net income and value of certain of our investments;

•	difficulties in staffing and managing international operations;

•	the imposition of governmental controls;

•	less favorable intellectual property or other applicable laws;

•	increasingly complex standards for complying with foreign laws and regulations that may differ substantially from country to country and may conflict with corresponding U.S. laws and regulations;

•	the far-reaching anti-bribery and anti-corruption legislation in the U.K., including the Bribery Act, and elsewhere and escalation of investigations and prosecutions pursuant to such laws;

•	the effects of the implementation of the U.K.’s decision to voluntarily depart from the E.U., known as Brexit;

•	compliance with complex import and export control laws;

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•	restrictions on direct investments by foreign entities and trade restrictions;

•	greater political or economic instability;

•	changes in tax laws; and

•	the imposition of tariffs or embargoes and other trade restrictions, including the recent tariffs imposed by the U.S. and China and the possibility of additional tariffs or other trade restrictions relating to trade between the two countries.

•	Risks of Reliance on Third Parties and Single Source Providers. We rely on third-party suppliers and manufacturers for many aspects of our manufacturing process for our products and product candidates. In some cases, due to the unique manner in which our products are manufactured, we rely on single source

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Risks Relating to Compliance with cGMP. We and our third-party providers are generally required to maintain compliance with cGMP and other stringent requirements and are subject to inspections by the FDA and comparable agencies in other jurisdictions to confirm such compliance. Any delay, interruption or other issues that arise in the manufacture, fill-finish, packaging or storage of our products as a result of a failure of our facilities or the facilities or operations of third parties to pass any regulatory agency inspection could significantly impair our ability to develop and commercialize our products. Significant noncompliance could also result in the imposition of monetary penalties or other civil or criminal sanctions and damage our reputation.

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Global Bulk Supply Risks. We rely on our principal manufacturing facilities for the production of drug substance for our large molecule products and product candidates. Our global bulk supply of these products and product candidates depends on the uninterrupted and efficient operation of these facilities, which could be adversely affected by equipment failures, labor shortages, natural disasters, power failures and numerous other factors.

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Risk of Product Loss. The manufacturing process for our products is extremely susceptible to product loss due to contamination, oxidation, equipment failure or improper installation or operation of equipment or vendor or operator error. Even minor deviations from normal manufacturing processes could result in reduced production yields, product defects and other supply disruptions. If microbial, viral or other contaminations are discovered in our products or manufacturing facilities, we may need to close our manufacturing facilities for an extended period of time to investigate and remediate the contaminant.

•	Reliance on Third Parties. We are dependent on the efforts of Samsung Bioepis and other third parties over whom we have limited or no control in the development and manufacturing of biosimilars products. If Samsung Bioepis or such other third parties fail to perform successfully, we may not realize the anticipated benefits of our investment in Samsung Bioepis;

•	Regulatory Compliance. Biosimilar products may face regulatory hurdles or delays due to the evolving and uncertain regulatory and commercial pathway of biosimilars products in certain jurisdictions;

•	Intellectual Property and Regulatory Challenges. Biosimilar products may face extensive patent clearances, patent infringement litigation, injunctions or regulatory challenges, which could prevent the commercial

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•	Failure to Gain Market and Patient Acceptance. Market success of biosimilar products will be adversely affected if patients, physicians and/or payors do not accept biosimilar products as safe and efficacious products offering a more competitive price or other benefit over existing therapies;

•	Ability to Provide Adequate Supply. Manufacturing biosimilars is complex. If we encounter any manufacturing or supply chain difficulties, we may be unable to meet higher than anticipated demand; and

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Competitive Challenges. Biosimilar products face significant competition, including from innovator products and from biosimilar products offered by other companies. In some jurisdictions, local tendering processes may restrict biosimilar products from being marketed and sold in those jurisdictions. The number of competitors in a jurisdiction, the timing of approval and the ability to market biosimilar products successfully in a timely and cost-effective manner are additional factors that may impact our success and/or the success of Samsung Bioepis in this business area.

•	the cost of restructurings or other initiatives to streamline our operations and reallocate resources;

•	impairments with respect to investments, fixed assets and long-lived assets, including in-process R&D and other intangible assets;

•	inventory write-downs for failed quality specifications, charges for excess or obsolete inventory and charges for inventory write downs relating to product suspensions, expirations or recalls;

•	changes in the fair value of contingent consideration;

•	bad debt expenses and increased bad debt reserves;

•	outcomes of litigation and other legal or administrative proceedings, regulatory matters and tax matters;

•	milestone payments under license and collaboration agreements; and

•	payments in connection with acquisitions and other business development activities.

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•	increase our vulnerability to general adverse economic and industry conditions;

•	limit our ability to access capital markets and incur additional debt in the future;

•	require us to dedicate a substantial portion of our cash flow from operations to payments on our indebtedness, thereby reducing the availability of our cash flow for other purposes, including business development efforts, research and development and mergers and acquisitions; and

•	limit our flexibility in planning for, or reacting to, changes in our business and the industry in which we operate, thereby placing us at a competitive disadvantage compared to our competitors that have less debt.

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•	800,000 square feet in Cambridge, MA, which is comprised of offices for our corporate headquarters, and other administrative and development functions and laboratories, of which 289,000 square feet is subleased by multiple companies for general office space, laboratories and manufacturing facilities; and

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•	357,000 square feet of office space in Weston, MA, of which 174,000 square feet is subleased through the remaining term of our lease agreement.

•	357,000 square feet of laboratory and office space;

•	188,000 square foot multi-purpose facility, including an ASO manufacturing suite and administrative space;

•	175,000 square feet related to a large-scale biologics manufacturing facility;

•	105,000 square feet related to a small-scale biologics manufacturing facility;

•	84,000 square feet of warehouse space and utilities;

•	70,000 square feet related to a parenteral fill-finish facility; and

•	43,000 square feet related to a large-scale purification facility.

•	139,000 square feet of warehouse, utilities and support space;

•	70,000 square feet related to a label and packaging facility;

•	50,000 square feet related to a laboratory facility; and

•	47,000 square feet of administrative space.

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(1)	On February 1, 2017, we completed the spin-off of our hemophilia business. Our consolidated results of operations and financial position reflect the financial results of our hemophilia business for all periods through January 31, 2017.

(2)	Product revenues, net reflect the impact of the following product launches:

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•	Commercial sales of SPINRAZA in the U.S. began in the fourth quarter of 2016 and in rest of world markets beginning in the first quarter of 2017.

•	Under our collaboration agreement with AbbVie, we began to recognize revenues on sales of ZINBRYTA to third parties in the E.U. in the third quarter of 2016. In March 2018 we and AbbVie announced the voluntary worldwide withdrawal of ZINBRYTA for RMS.

•	Under our commercial agreement with Samsung Bioepis, we began to recognize revenues on sales of BENEPALI and FLIXABI to third parties in the E.U. in the first and third quarters of 2016, respectively, and began to recognize revenues on sales of IMRALDI to third parties in the E.U. in the fourth quarter of 2018.

•	Commercial sales of ALPROLIX commenced in the second quarter of 2014 and commercial sales of ELOCTATE and PLEGRIDY commenced in the third quarter of 2014. We stopped recognizing product revenues from ALPROLIX and ELOCTATE effective February 1, 2017,upon the completion of the spin-off of our hemophilia business.

(3)	Net income (loss) attributable to noncontrolling interests, net of tax includes the following activity:

•	Pre-tax charges of $50.0 million and $150.0 million for the years ended December 31, 2018 and 2017, respectively, for payments made under the terms of the Neurimmune Agreement in exchange for reductions in the previously negotiated royalty rates payable on products developed under the Neurimmune Agreement, including royalties payable on potential commercial sales of aducanumab.

•	A pre-tax charge of $60.0 million for the year ended December 31, 2015, for a milestone payment due to Neurimmune upon the enrollment of the first patient in a Phase 3 study for aducanumab.

(4)	Total Biogen Inc. shareholders' equity reflects the repurchase of approximately 40.0 million shares of our common stock at a cost of approximately $11.7 billion between December 31, 2014 and December 31, 2018:

•	During 2018 we repurchased and retired approximately 4.3 million and 10.5 million shares of our common stock at a cost of approximately $1.4 billion and $3.0 billion under our 2018 and 2016 Share Repurchase Programs, respectively.

•	During 2017 we repurchased and retired approximately 3.7 million shares of our common stock at a cost of approximately $1.0 billion under our 2016 Share Repurchase Program.

•	During 2017 we repurchased approximately 1.2 million shares of our common stock at a cost of $365.4 million under a program authorized by our Board of Directors in February 2011 for the repurchase of up to 20.0 million shares of our common stock (2011 Share Repurchase Program).

•	During 2016 we repurchased and retired approximately 3.3 million shares of our common stock at a cost of approximately $1.0 billion under our 2016 Share Repurchase Program.

•	During 2015 we repurchased and retired approximately 16.8 million shares of our common stock at a cost of $5.0 billion under a program authorized by our Board of Directors in May 2015 for the repurchase of up to $5.0 billion of our common stock.

(5)	Notes payable, less current portion reflect:

•	Our 2017 repayment of our 6.875% Senior Notes that were issued in 2008 with an aggregate principal amount of $550.0 million; and

•	The issuance of our senior unsecured notes for an aggregate principal amount of $6.0 billion in September 2015.

(a)

Total cost and expenses for the year ended December 31, 2018, includes a pre-tax charge to research and development expense of $486.2 million upon the closing of the 2018 Ionis Agreement. Included in this amount was a charge of $162.1 million reflecting the premium paid above fair value for the purchase of approximately 11.5 million shares of Ionis' common stock upon the closing of the 2018 Ionis Agreement. This charge is partially offset by net gains totaling $100.9 million recognized in other income (expense), net for the year ended December 31, 2018, related to these shares. For further information on our collaboration arrangements with Ionis, please read Note 19, Collaborative and Other Relationships, to our consolidated financial statements included in this report.

(b)	Total cost and expenses for the year ended December 31, 2018, includes the impact of impairment charges totaling $189.3 million related to certain in-process research and development (IPR&D) assets associated with our vixotrigine (BIIB074) program.

(c)	Total cost and expenses for the year ended December 31, 2018, includes pre-tax charges to acquired IPR&D totaling $112.5 million for upfront payments made to AliveGen, Pfizer and Karyopharm upon the closing of our asset purchase

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(d)

Income tax expense for the year ended December 31, 2017, includes a $1,173.6 million provisional estimate pursuant to SEC Staff Accounting Bulletin No. 118. Our provisional estimate included an amount of $989.6 million associated with the Transition Toll Tax and $184.0 million related to the impact of remeasuring our deferred tax balances to reflect the new federal statutory rate and other changes to U.S. tax law.

(e)	Total cost and expenses for the year ended December 31, 2016, includes a pre-tax charge of $454.8 million related to our January 2017 settlement and license agreement with Forward Pharma A/S (Forward Pharma).

(f)

Total cost and expenses for the year ended December 31, 2017, includes pre-tax charge of $300.0 million for an upfront payment made to BMS upon entering into our agreement to exclusively license BIIB092 and a pre-tax charge of $60.0 million for a development milestone that became payable to the former shareholders of iPierian, Inc. (iPierian) upon the dosing of the first patient in the Phase 2 study of BIIB092 for PSP.

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