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 Progenics Pharmaceuticals (PGNX), a developer of therapies focused on treating cancer and providing oncology supportive care, dropped as much as 30% after abstracts of its mid-stage study involving experimental prostate cancer antibody-drug conjugate, PSMA-ADC, revealed the death of two patients.

So what: According to a Bloomberg report -- since Progenics has yet to make an official comment yet, but has scheduled a webcast of its mid-stage results for tomorrow -- and the posted abstracts, two prostate cancer patients died of sepsis in its ongoing trial and, as Stifel Nicolaus analyst Brian Klein noted in his interview with Bloomberg, it would suggest that PSMA-ADC has "a major impact on the immune system." The study abstract also appears to show that even lower doses of the drug may result in dangerous levels of toxicity.

Now what: This is certainly not good news for Progenics shareholders, who had high hopes that the company's ADCs would work in similar fashion to other cancer-focused ADCs currently being tested by companies like Seattle Genetics and ImmunoGen. Based on these abstracts, though, it would appear that further testing on PSMA-ADC might be pointless due to the toxicity concerns of the drug. We obviously can't make the determination for certain of whether or not PSMA-ADC will advance to a later stage trial until Progenics reports its findings tomorrow, but I'd say the pendulum is definitely swinging toward this compound being discontinued for safety reasons instead of continuing to be developed.