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 biotechnology company ImmunoGen (NASDAQ:IMGN) plummeted 18% today after deciding to stop a phase 2 study of its experimental small-cell lung cancer drug because it didn't appear to be working.

So what: The trial's independent data monitoring committee concluded that IMGN901 was unlikely to show a sufficient improvement to justify continuing the trial, prompting ImmunoGen to end the study and, in the process, dash investors' short-term hopes for the pipeline. Specifically, analysts don't expect ImmunoGen to move forward with IMGN901 in any other indications due to the poor results, raising plenty of uncertainty over its growth trajectory.

Now what: ImmunoGen will probably now have to focus on the preclinical compounds in its pipeline. "This is clearly a disappointing outcome, as there is a tremendous need for new treatment options for SCLC," said ImmunoGen Chief Development Officer Dr. Charles Morris. "We will be analyzing the findings to date in this trial as part of assessing potential next steps for IMGN901." But while ImmunoGen is still too speculative for average Fools, today's big drop -- the stock is now off 35% from its 52-week high -- might be an attractive opportunity for biotech-savvy contrarians.