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 drug company Rigel Pharmaceuticals (NASDAQ:RIGL) plummeted 34% today after the experimental rheumatoid arthritis drug it is licensing to AstraZeneca (NASDAQ:AZN) failed to meet one of two primary objectives in a clinical study.

So what: While fostamatinib showed superior results compared to a placebo in the mid-stage study, it proved inferior to Abbott Laboratories' (NYSE:ABT) Humira, dealing a huge setback to Rigel's revenue prospects going forward. Part of Rigel's deal with AstraZeneca involves receiving sales-related milestone payments if the drug achieves commercial success, as well as hefty double-digit royalties, so it's no surprise that the stock is setting a new 52-week low on the faded hopes.

Now what: AstraZeneca said the results should not be taken as definitive and that there are larger studies to come.

"A more comprehensive assessment of the benefit/risk profile of fostamatinib used in combination with a DMARD is being undertaken in the pivotal studies that form the OSKIRA Phase III programme which are on track to report in the first half of 2013, and would form the basis of regulatory submissions," said Martin Mackay, president of AstraZeneca R&D.

Given today's disappointing results, however, Rigel investors shouldn't set their expectations too high.

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.