Biogen's Spinraza took a 100% leap and its multiple sclerosis franchise mostly held its own in the second quarter, but analysts weren't much interested in those topics on Tuesday morning's earnings call. Instead, they peppered executives with questions about Wednesday's highly anticipated Alzheimer's data.

In fact, the data—to be presented Wednesday in Chicago by Biogen's partner Eisai—are so important they could send Biogen's shares up $20 or down $40, Leerink analyst Geoff Porges wrote last week. And so, on Tuesday's call, much of the Q&A focused on aspects of the data release and the company's plans with the candidate, BAN2401.

Executives couldn't answer all of the questions ahead of the release, and the call also included discussion about the company's positive commercial results during the quarter. Biogen beat Street sales estimates, turning in 9% revenue growth to $3.4 billion. Spinal muscular atrophy med Spinraza contributed significantly to the increase, with its sales more than doubling to $423 million.

Biogen's multiple sclerosis business turned in $2.3 billion in second-quarter sales, down 2% compared with the same period last year. While a slight decline, that was a rebound from the 4% drop the business posted in the first quarter. In the most recent period, Tecfidera sales slipped 2% to $1.09 billion. Sales for interferon drugs Avonex and Plegridy fell 9% to $626 million, and Tysabri also fell 6% to $467 million. On the flip side, Biogen received $113 million in royalties—a new revenue stream—from sales of Roche's Ocrevus.

On the earnings call, executives said they're looking forward to moving out of tough comparison quarters against Ocrevus as that drug launched last spring and quickly scooped up market share in subsequent periods, hurting sales for Biogen MS meds. With the second-quarter results, the company increased its guidance for the year to a range of $13 billion to $13.2 billion, from a range of $12.7 billion to $13 billion. 

Even with the strong sales, analysts were focused elsewhere. Many asked about BAN2401, data for which Eisai is presenting Wednesday at the Alzheimer's Association International Conference in Chicago.

A phase 2 trial on the drug initially turned in poor results last December based on a Bayesian analysis at 12 months. But Biogen and Eisai opted to keep the trial blinded through 18 months of follow-up. And early this month, the partners reported that the drug demonstrated statistically significant slowing of Alzheimer's symptoms, plus a reduction of amyloid beta accumulated in the brain. The topline results sent Biogen's shares significantly upward, as they also boosted chances of success for another Alzheimer's candidate, aducanumab. New data for that drug aren't expected until 2020, so analysts and investors are watching progress with BAN2401 closely. Both drugs are Beta amyloid antibodies.

Eisai is presenting the BAN2401 results Wednesday afternoon at AAIC, and Biogen has a conference call scheduled for the evening to discuss its Alzheimer's portfolio.