What happened

Shares of ImmunoGen Inc. (NASDAQ:IMGN) were down 8% as of 3:51 p.m. EDT on Friday after falling as much as 10.7% earlier in the day. As was the case on Thursday, when the biotech stock fell by a double-digit percentage, there was no news explaining the decline.

So what

Significant swings in the stock prices for clinical-stage biotechs like ImmunoGen aren't unusual -- even when there appears to be no underlying cause. Even with the declines this week, though, the stock is still up more than 24% year to date.

Businessman looking at red line going through floor

Image source: Getty Images.

Investors need to keep the big picture in mind with any stock, but especially with ImmunoGen. The company has several clinical studies in progress that are key. The most important of these is the phase 3 study evaluating mirvetuximab as a monotherapy in treating ovarian cancer.

ImmunoGen also has several phase 2 studies of mirvetuximab as part of combination therapies. A couple of those studies feature ImmunoGen's lead drug with cancer drug Avastin. The biotech is also evaluating mirvetuximab in combination with Merck's powerful immunotherapy Keytruda.

Now what

The best thing that ImmunoGen shareholders can do now is wait. Results from the phase 3 study of mirvetuximab as a monotherapy for treating ovarian cancer won't be released until 2019. However, data from the phase 2 combo study with Keytruda will be announced later in October. ImmunoGen also expects to report phase 1 results for a couple of other pipeline candidates, IMGN779 and IMGN632, in December. 

Could there be more big swings between now and the end of the year? Sure. Some of those gyrations could be like this week's moves: much ado about nothing. The real key for ImmunoGen is how mirvetuximab fares in the clinical studies. Until those results are known, everything else that happens is likely to only be noise.  

Keith Speights has no position in any of the stocks mentioned. The Motley Fool recommends ImmunoGen. The Motley Fool has a disclosure policy.