Biogen Inc. (BIIB) delivered a pleasant surprise Friday, beating Wall Street expectations on both the top and bottom lines as its portfolio of newer drugs continues gaining traction. The biotech company reported adjusted earnings per share of $1.99 for the fourth quarter, easily clearing the consensus estimate of $1.59.

Revenue came in at $2.28 billion, topping expectations of $2.20 billion, though that still represents a 7% decline on both a reported and constant currency basis. The real story here isn't the overall decline but rather what's driving the numbers underneath.

The New Guard vs. The Old Guard

Biogen's transformation is playing out in real time. The company's growth products saw revenue jump 19% year-over-year in fiscal 2025, offsetting declines from its legacy multiple sclerosis franchise. It's the classic pharmaceutical story: newer drugs gaining momentum while older ones face patent cliffs and competition.

The Alzheimer's drug Leqembi generated collaboration revenue of $47 million during the quarter, with total in-market sales hitting around $134 million—up 54% from the prior period. Those sales are booked by partner Eisai, with U.S. in-market sales reaching approximately $78 million and showing continued growth. For a drug tackling one of medicine's toughest challenges, that trajectory matters.

Meanwhile, the multiple sclerosis business continues its retreat. MS revenue fell 14% to $917 million, with Tysabri dropping to $397.5 million from $415.4 million in the year-ago quarter. It's a steady erosion that Biogen clearly anticipated.

Winners and Losers in the Portfolio

The rare disease segment saw revenue dip 4% year-over-year to $514.6 million. Spinraza, a treatment for spinal muscular atrophy, declined to $356.2 million from $421.4 million a year earlier. Fourth quarter Spinraza revenue fell 15% year-over-year, partly due to timing of shipments outside the U.S., though full-year revenue was only down 2%.

On the bright side, Skyclarys—the Friedreich's ataxia drug Biogen picked up through its Reata acquisition—posted revenue of $133.4 million in the quarter, up from $102.2 million a year ago. The drug grew its global patient base by roughly 30% during 2025. Fourth quarter U.S. revenue hit approximately $89 million driven by demand growth, while international revenue reached around $44 million, reflecting continued demand expansion along with a one-time reimbursement adjustment.

Zurzuvae, Biogen's postpartum depression treatment, delivered approximately $66 million in fourth quarter revenue with strong ongoing demand growth. Even Vumerity managed a 3% year-over-year gain in the fourth quarter, reaching $181.1 million.

"Our 2025 performance reflected continued focus on strong execution and financial discipline, driven by our revenue of nearly $1 billion from LEQEMBI, SKYCLARYS, ZURZUVAE, and QALSODY, progression of our pipeline, and resilience of our MS franchise," said Christopher Viehbacher, President and CEO.

Looking Ahead to 2026

Biogen's guidance for fiscal 2026 came in above expectations, projecting earnings between $15.25 and $16.25 per share compared to the consensus estimate of $14.92. That's confidence.

The company expects revenue to decline by mid-single digits compared to 2025, as further drops in multiple sclerosis product revenue (excluding Vumerity) are partially offset by increases from growth products. Specifically, MS product revenue excluding Vumerity is forecast to fall by a mid-teen percentage versus fiscal 2025, while biosimilars are expected to continue declining by low double-digit percentages.

Biogen also anticipates roughly $300 million in contract manufacturing revenues in each half of 2026.

Stock Performance: Biogen shares climbed 4.28% to $193.29 at the time of publication Friday, marking a new 52-week high for the stock.