Immunogen’s full data on mirvetuximab soravtansine have underwhelmed investors. While the biotech is racing to the FDA with the results, its stock fell around 20% to below $5 in premarket trading after the release of survival data that fell short of investor expectations.
Late last year, Immunogen reported top-line data from a phase 3 clinical trial of antibody-drug conjugate mirvetuximab in patients with folate receptor alpha-high, platinum-resistant ovarian cancer. The readout emboldened Immunogen to plot out a path to its first approval, only for the full data drop Sunday to raise questions about the prospects of mirvetuximab.
Median progression-free survival (mPFS) came in at 4.3 months when assessed by the investigator and 5.5 months when assessed by blinded independent central review. After seeing the data, analysts at Jefferies sought to put the “seemingly short-of-expectations” 4.3-month mPFS into context.
According to the analysts, the SORAYA trial enrolled more heavily pretreated patients than earlier studies that primed investors to expect a better result. All 106 participants had previously received Avastin, which the analysts said “likely has a big impact on mPFS,” and almost half had been treated with a prior PARP inhibitor. The assessment has implications for Immunogen’s next phase 3 readout, MIRASOL.
“It seems that prior [Avastin] negatively impacts pts who achieve stable disease. Therefore, the patient % w/ prior [Avastin] in MIRASOL could be critical to success,” the analysts wrote in a note to investors. As SORAYA had an unusually high proportion of patients treated with Avastin, the analysts think the earlier FORWARD1 study may provide a better guide to the likely mPFS in MIRASOL.
Immunogen is running MIRASOL, top-line data from which are due in the third quarter, to support the full approval of mirvetuximab. The SORAYA results will form part of the package of data the biotech plans to use to win accelerated approval in the U.S. A filing with the FDA is planned for this month.