* Spinraza sales beat analysts' estimates
* Shares up slightly in early trading
* MS drug Tecfidera misses analyst estimates (Adds CEO, analyst comment, share movement, Spinraza details from conference call)
By Manas Mishra and Saumya Joseph
Oct 23 (Reuters) - Biogen Inc on Tuesday handily beat Wall Street expectations for third quarter profit, led by strong demand for its new blockbuster muscle disease treatment Spinraza.
Shares of the U.S. biotech company were up nearly 1 percent at $318.14 as investors await updated data from two of Biogen's experimental Alzheimer's disease treatments at a medical meeting this week.
Spinraza, the first approved treatment for spinal muscular atrophy (SMA) and the company's most important future growth driver, had sales of $468 million for the quarter, exceeding analysts' estimates of $448.1 million, according to Refinitiv data.
The treatment, which has already exceeded $1 billion in sales for the year, was helped by a 20 percent jump in new patients over the second quarter, with adults accounting for more than half of new patients.
Biogen said nearly 6,000 patients are taking Spinraza, with the majority of the treatable infant SMA population already receiving the drug.
As Biogen prepares for future competition for Spinraza and sales growth of its top-selling oral multiple sclerosis (MS) drug Tecfidera slows, Biogen executives touted its pipeline of high-risk drugs in development, including several for Alzheimer's, as well as experimental treatments for ALS, severe stroke and next generation MS drugs.
"We have some very important results in the coming months," Chief Executive Officer Michel Vounatsos said on a conference call. "In the meantime, we deliver, we tighten the belts, and we are evaluating opportunities."
Excluding items, Biogen said it earned $7.40 per share, well above analysts' average estimate of $6.78, according to Refinitiv estimates.
"All in all, top- and bottom-line beat should lead to a modest positive reaction and alleviate any near-term concerns on the ongoing core business," Jefferies analyst Michael Yee said.
Biogen will present data on its high-profile Alzheimer's drug, aducanumab, this week. Eisai Co Ltd is also expected to discuss another experimental treatment for the mind-wasting disease being developed in partnership with Biogen at the meeting.
The company said sales of its MS treatments were helped by U.S. price increases.
Tecfidera sales rose 1.9 percent to $1.09 billion, shy of analysts' estimates of $1.11 billion. Tysabri, a long-acting injectable MS drug, had sales of $470 million, above expectations of about $453 million.
Tecfidera is facing stiff competition from Roche AG's Ocrevus. However, Biogen collected $137 million in Ocrevus royalty revenue in the quarter.
Total revenue rose 11.7 percent to $3.44 billion, exceeding analysts' estimates of $3.33 billion. (Reporting by Manas Mishra and Saumya Sibi Joseph in Bengaluru; Editing by Sriraj Kalluvila and Bill Berkrot)