MorphoSys’ pelabresib meets PhIII primary endpoint but misses on key secondary

MorphoSys is declaring success on a Phase III study involving the key cancer drug from its $1.7 billion buyout of Constellation, but a secondary endpoint miss appears to be causing concern.

The MANIFEST-2 trial tested MorphoSys’ BET inhibitor, pelabresib, in combination with Incyte’s ruxolitinib (sold, among other names, as Jakafi), as a treatment for a rare blood cancer called myelofibrosis. The combo met the primary endpoint, demonstrating a statistically significant improvement in the proportion of patients achieving at least a 35% reduction in spleen volume — a metric also known as SVR35 — at week 24.

In total, 66% of patients receiving the duo hit SVR35, compared to only 35% of those receiving placebo plus ruxolitinib (p<0.001).

However, pelabresib and ruxolitinib missed statistical significance on a secondary endpoint, TSS50, which measures the proportion of patients achieving at least a 50% reduction in total symptom score.

MorphoSys shares fell more than…
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