ImmunoGen lines up FDA filing as antibody-drug conjugate shrinks tumors in pivotal trial

After toiling for 40 years, ImmunoGen can now see the potential approval of its first wholly owned oncology drug on the horizon. The biotech is preparing to submit mirvetuximab soravtansine for approval after showing the antibody-drug conjugate (ADC) shrank ovarian tumors. 

Investigators enrolled 106 patients with folate receptor alpha-high, platinum-resistant ovarian cancer who had received up to three prior lines of therapy to receive mirvetuximab. Half of the subjects had received three lines of therapy. All participants had previously received Avastin, and almost half had taken a PARP inhibitor.

In that population, mirvetuximab, a drug designed to fire guided chemotherapy missiles at cancer cells that express high levels of folate receptor alpha, achieved a 32% objective response rate (ORR). Responses were seen regardless of whether a patient had received a PARP inhibitor and independent of the number of lines of therapy. Five people had complete responses. 

The response rate was high enough for the single-arm study to meet its primary endpoint, which required the lower bound of the confidence interval to beat the 12% ORR seen in an earlier trial of single-agent chemotherapy. At 24%, the lower bound of the confidence interval came in well above the efficacy bar set in the chemotherapy study.

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Away from the primary endpoint, ImmunoGen reported a median duration of response (DOR) of 5.9 months. That figure could change as the data mature. With almost half of responders still on the drug, ImmunoGen foresees the final DOR landing in the range of 5.7 months to around seven months.

On the safety front, 41% of patients experienced blurred vision, and 35% of subjects had the eye disease keratopathy. Six percent of patients had grade 3 or worse blurred visio,n and 9% of subjects had grade 3 or worse keratopathy. Seven percent of patients dropped out of the clinical trial because of treatment-related adverse events, which also necessitated dose reductions and delays in 19% and 32% of participants, respectively. 

Armed with the data, ImmunoGen plans to file for FDA approval in the first quarter of next year before going on to confirm the results in a second study that is due to deliver data later in 2022. Shares in ImmunoGen rose around 30% to above $6 in premarket trading as investors reassessed the prospects of a drug some people are framing as a significant advance for ovarian cancer patients. 

“Response rates with available therapy are in the single digits with significant toxicities,” Dana-Farber Cancer Institute’s Ursula Matulonis, M.D., co-principal investigator of the trial, said in a statement. “With an ORR above 30%, a duration of response of around six months, and a treatment-related discontinuation rate below 10%, mirvetuximab shows impressive activity and tolerability for patients with platinum-resistant ovarian cancer.”

The biotech's shares were up 30% in mid-morning trading Tuesday.