Every month brings plenty of catalysts for several biotech stocks. October is no exception. There are quite a few regulatory decisions and clinical results expected to be announced next month.

Three biotechs in particular could enjoy boosts to their stocks if all goes well. Here are the major catalysts that could help -- or possibly hurt -- Alexion Pharmaceuticals (NASDAQ:ALXN), bluebird bio (NASDAQ:BLUE), and Sarepta Therapeutics (NASDAQ:SRPT).

October 2017 calendar on wooden wall

Image source: Getty Images.

Alexion Pharmaceuticals

Alexion became one of the most successful biotechs in the world on the strength of Soliris. Momentum for Soliris continued in the second quarter. The drug is currently used to treat two rare diseases, paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome (aHUS). Alexion hopes to soon add a third indication to the list. The U.S. Food and Drug Administration expects to announce an approval decision for Soliris in treating refractory generalized myasthenia gravis (gMG) patients who are anti-acetylcholine receptor (AChR) antibody-positive by Oct. 23. 

How big of a deal would an approval be for Alexion? There are somewhere between 60,000 and 80,000 patients in the U.S. with myasthenia gravis. Around 5% to 10% of those have refractory gMG and are AChR-positive -- target candidates for Soliris. That might not seem like a lot, but even on the low end it's a lot higher than the estimated 650 to 1,800 patients in the U.S. with aHUS. 

However, the biotech's phase 3 study evaluating the drug in refractory gMG failed to meet its primary endpoint of improvement in a standard patient self-assessment. But because the primary endpoint was only narrowly missed and other data from the study pointed to potential efficacy, Alexion moved forward with its regulatory submission.  The company has already received some good news: Soliris recently won European approval in the refractory gMG indication.

Bluebird 

Bluebird already provided some initial data from its on-going phase 2/3 Starbeam study evaluating its Lenti-D gene therapy in treating boys with cerebral adrenoleukodystrophy (CALD). However, the biotech is scheduled to announce an updated data set at the Child Neurology Society 2017 annual meeting on Oct. 5. 

The already-presented data was encouraging in that 15 out of 17 patients who completed two years of follow-up after treatment with Lenti-D were free of major functional disabilities. However, details were sparse, particularly on the safety profile of the gene therapy. 

Should Bluebird succeed in the Starbeam study, its opportunities are great. The only effective treatment for CALD right now is allogeneic hematopoietic stem-cell transplant (HSCT). However, there are serious and sometimes fatal potential complications that can result from HSCTs. 

Sarepta Therapeutics

Sarepta Therapeutics has already racked up greater success than many expected with its Duchenne muscular dystrophy (DMD) drug, Exondys 51. The biotech posted terrific second-quarter results, with its only approved drug trouncing analysts' revenue estimates. More good news could be on the way when Sarepta provides additional data from its phase 1/2 study of experimental drug golodirsen in treating DMD patients amenable to skipping exon 53 at the World Muscle Society meeting in early October. (Exons are a segment of DNA that codes for a specific protein.)

Earlier this month, Sarepta announced initial results from that study that sent its stock 11% higher. Those results showed golodirsen was even more effective at producing muscle protein dystrophin than Exondys 51. Boys with DMD suffer from a lack of dystrophin.

Exondys 51 only targets DMD patients amenable to skipping exon 51. Around 13% of DMD patients fit this criterion, while another 8% of patients are amenable to skipping exon 53, which golodirsen targets. The second drug definitely represents another huge opportunity for Sarepta -- if it can ultimately win approval.

Keith Speights has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Bluebird Bio. The Motley Fool has a disclosure policy.