FDA tells ImmunoGen to run a second phase 3, sinking stock

ImmunoGen CEO Mark Enyedy
ImmunoGen CEO Mark Enyedy (ImmunoGen)

The FDA has quashed ImmunoGen’s hopes of filing for approval of mirvetuximab soravtansine on the strength of a failed phase 3 trial. FDA officials advised ImmunoGen a run a new phase 3 in patients with high folate receptor alpha (FRα)-positive, platinum-resistant ovarian cancer before seeking approval.

ImmunoGen’s first phase 3 found anti-FRα antibody-drug conjugate (ADC) mirvetuximab soravtansine failed to improve on the progression-free survival achieved by chemotherapy. But ImmunoGen zeroed in on the performance of the ADC in a prespecified population of patients with high FRα expression to keep its hopes of a near-term filing for approval alive.

Now, ImmunoGen has revealed the FDA snuffed out those hopes at a recent meeting. ImmunoGen hoped to persuade the FDA to accept a submission based on the subgroup analysis, setting it up to file for approval by the end of 2019. But the FDA saw the primary endpoint fail as a barrier to filing.   


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Instead, the FDA has recommended that ImmunoGen run a new phase 3 trial in patients with high FRα expression, the subpopulation in which an efficacy signal was seen in the original trial. The news puts ImmunoGen’s plans well back but was expected by many observers. 

“We viewed it as unlikely that the FDA would consider a subgroup analysis, given the totality of the FORWARD I data disclosed. However, we do expect the stock to be weak today as some investors were hoping that the FDA would consider approving mirvetuximab for the FRα-high subgroup, based on the existing data,” analysts at SVB Leerink wrote in a note to investors.

Shares in ImmunoGen fell by more than 30% in premarket trading, more than wiping out the gains it made after talking up the subgroup analysis on its quarterly results conference call early this month. 

ImmunoGen is publicly taking the positives from the FDA meeting, with CEO Mark Enyedy framing it as helping the company “clarify a regulatory path forward for mirvetuximab” in a statement about the news. Enyedy went on to say ImmunoGen is “evaluating all avenues to bring this promising therapy to ovarian cancer patients.”

The company ended the first quarter with $270 million in cash and cash equivalents, but that may be depleted quickly. Before learning of the phase 3 failure, ImmunoGen forecast it would have up to $140 million in cash come the end of the year. To make its cash go further, ImmunoGen is carrying out a strategic review. Earlier this month, Enyedy said ImmunoGen would release the results of the review after meeting with the FDA.  

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