Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Agenus (NASDAQ:AGEN), a biopharmaceutical company focused on developing novel immunotherapies to treat cancer and a number of other unmet diseases, tumbled by as much as 22% after partner GlaxoSmithKline (NYSE:GSK) announced that its phase 3 MAGE-A3 cancer immunotherapeutic trial in non-small cell lung cancer (NSCLC) patients didn't meet its first or second coprimary endpoint.

So what: According to Glaxo's press release, the study contains Agenus' QS-21 adjuvant, which is being studied in more than a dozen different programs at the moment, but it didn't extend the disease-free survival period relative to the control arm in MAGE-A3 positive patients or patients who were chemotherapy-naive. GlaxoSmithKline intends to continue its study until the analysis of a third coprimary endpoint focused on a very specific group of patients identified to have gene signatures that may allow them to benefit most is complete. Glaxo anticipates this data will be available sometime in 2015.

Now what: Not a good way to start the day if you're an Agenus shareholder. On one hand this is incredibly worrisome because its QS-21 adjuvant program is its furthest along in studies and gives Agenus its best shot at reducing its cash burn through revenue generation. If QS-21 isn't working in NSCLC, there are concerns that it may prove ineffective in other ongoing studies. But shareholders should also realize that other types of cancer and diseases can respond markedly different to the same therapy. Because Agenus has such an extensive pipeline of ongoing studies, both clinical and preclinical in nature, it gives Agenus plenty of chances to hit a home run. Plus, it's hard to overlook a solid collaborative partnership with a global giant like GlaxoSmithKline. I'm not ready to call today's drop a buying opportunity just yet, but I wouldn't suggest preaching doom and gloom on Agenus, either.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.