"The lack of a randomized study combined with the heterogeneous patient population regarding AML prognostic factors makes interpretation of the study results difficult," said the FDA in comments prepared for an advisory review panel. The panel is due to meet on Tuesday to determine Clolar's fate.

Investors are taking the news in stride today, with GENZ trading on just a fractional loss. The equity was once again rejected this week by resistance at its 32-week moving average, which has capped all but one of the stock's weekly closes since October 2008.

Today's muted reaction to the troubling Clolar news could be due to the fact that there's plenty of pessimism priced into the shares already. Short interest on GENZ jumped by 8.6% during the most recent reporting period, and these bearish bets now account for 2.3% of the equity's available float.

Option players are similarly downbeat. During the past 10 days, traders on the International Securities Exchange (ISE) have bought to open 1.20 puts for every call on GENZ. This put/call volume ratio ranks higher than 79.3% of other such readings taken during the past year, revealing that traders are picking up puts over calls at a faster pace than usual.

However, the troubled stock could still be vulnerable to downgrades if the FDA's Clolar verdict is unfavorable. Zacks reports 13 Buy or better ratings from analysts, compared to just two Holds and no Sells. Any downgrades from this group could draw fresh selling pressure to the security.

Elizabeth Harrow is an analyst and financial writer in the research department at Schaeffer's Investment Research. She is featured in the video series Schaeffer's Daily Q&A on SchaeffersResearch.com.