Strike two for patritumab deruxtecan

Anyone shocked at the numbers revealed in the ASCO abstract on patritumab deruxtecan's Herthena-Lung02 study had good reason to worry. Daiichi Sankyo and Merck & Co on Thursday withdrew the anti-HER3 ADC's US filing for relapsed EGFR-mutated non-small cell lung cancer, citing Herthena-Lung02's overall survival result, which they revealed didn't meet statistical significance. This is a fresh problem for patritumab, which Merck licensed from Daiichi for $1.5bn up front; the filing, based on the phase 2 Herthena-Lung01 trial, had already been hit with a complete response letter last June, but that was put down to a third-party manufacturing technicality. Now the issue is with Herthena-Lung02, the potential confirmatory trial whose positive primary PFS readout was shown by ASCO to amount to a 0.77 hazard ratio (p=0.011), but a median PFS improvement of just 0.4 months, versus chemo. The revelation that OS is a bust is perhaps not surprising, but for it to have led to the filing being pulled suggests that patritumab might be numerically detrimental to survival. Attention now turns to ASCO on Sunday, when the full Herthena-Lung02 results will be presented, allowing the precise numbers, and the shapes of PFS and OS curves, to be scrutinised.

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