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Why Onconova Therapeutics Inc. Shares Imploded

By Sean Williams - Feb 20, 2014 at 1:01PM

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Onconova Therapeutics reported disappointing phase 3 results for high-risk myelodysplastic syndrome drug rigosertib. Is this sell-off a buying opportunity or a reason to leave and not turn back?

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 Onconova Therapeutics (ONTX 0.00%), a clinical-stage biopharmaceutical company focused on developing therapies to treat cancer, nosedived as much as 44% after the company announced disappointing results from its phase 3 ONTIME trial of rigosertib in higher-risk myelodysplastic syndrome, or MDS, patients who had progressed or relapsed while using hypomethylating agents, or HMA.

So what: Onconova said in a press release issued after the bell last night that rigosertib did not meet the primary endpoint compared to the best supportive care, or BSC, control arm. Median overall survival in the Onconova intent-to-treat group was 8.2 months, compared to 5.8 months in the best supportive care arm. Because of an extremely high p-value (0.27), there's a strong possibility that chance rather than medical benefit from rigosertib was involved in these results, making this 2.4 month difference not statistically significant.

If there was a bit of sunshine on this cloudy day, it's that a post-hoc analysis showed that a smaller subset of patients who had not responded to HMAs demonstrated a median overall survival of 8.5 months versus 4.7 months in the BSC arm. These results were statistically significant with a low p-value and a hazard ratio of 0.67, implying a 33% reduction in death risk while taking rigosertib.

Now what: There's certainly not a lot of positives that can be taken from yesterday's phase 3 results. The saving grace here might be that post-hoc analysis which is unlikely to result in rigosertib being scrapped in its entirety for high-risk MDS. However, Onconova can kiss a larger indication for secondary treatment to MDS goodbye for higher-risk patients. There's still a chance rigosertib performs better in low-risk patients, for which midstage studies are ongoing, but I wouldn't hold your breath. The real concern here is that if rigosertib proves to be a wash, Onconova has only two other ongoing early stage clinical studies. The remainder of its pipeline is preclinical in nature, meaning the company could still have additional downside left in its share price.

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