ImmunoGen touts 'home run' as ovarian cancer drug Elahere extends lives in landmark trial win

ImmunoGen has shaken off a previous phase 3 flop for its ovarian cancer antibody-drug conjugate Elahere with what its CEO is calling a “home run” trial success. 

In a pleasant surprise to ImmunoGen investors, Elahere slashed the risk of death by 33% compared with chemotherapy in certain patients with previously treated ovarian cancer, the Massachusetts biotech said Wednesday.

The phase 3 MIRASOL trial win makes Elahere the first medicine to show an overall survival advantage in platinum-resistant ovarian cancer, the company was quick to point out.

The trial is a “home run,” CEO Mark Enyedy said during an investor call Wednesday. The trial not only hit its primary goal on tumor progression but also on tumor shrinkage and life extension in an unprecedented showing, he said.

Based on the readout, SVB Securities analysts increased their peak U.S. sales estimate for the drug in this indication to $210 million from $170 million.

An FRα-directed ADC, Elahere gained FDA accelerated approval in late 2022 in previously treated, FRα-positive ovarian based on data from a single-arm trial showing it could shrink tumors in 32% of patients. But investors and analysts remained skeptical at the time of the approval because the drug had previously failed in a phase 3 study in platinum-resistant ovarian cancer patients with medium to high levels of FRα.

The current MIRASOL trial was designed as the confirmatory trial to turn Elahere’s conditional FDA nod into a full one and to serve as the basis for approvals outside the U.S. The trial enrolled patients with platinum-resistant ovarian cancer with high FRα expressions who have received one to three prior lines of therapy.

In the new study, Elahere reduced the risk of disease progression or death by 35%. Patients on Elahere went a median 5.6 months without progression, whereas the chemo arm chalked up nearly four months of progression-free time.

The progression-free survival (PFS) win was largely expected, SVB analysts said in their Wednesday note to clients. But the positive overall survival result came as a surprise and should “alleviate any concerns on the clinical meaningfulness of the absolute difference in median PFS.”

In the trial, patients who took Elahere lived a median 16.5 months, compared with 12.8 months for chemo.

Thanks to the overall survival win, physicians will view Elahere “as groundbreaking and paradigm-changing” in the disease setting, William Blair analysts said in a separate note to clients Wednesday.

Most patients in the control arm received the chemotherapy paclitaxel, ImmunoGen’s chief medical officer Anna Berkenblit, M.D., told investors on Wednesday’s call. That makes the trial win especially valuable, William Blair analysts said, because paclitaxel has historically demonstrated the best efficacy compared with other chemo regimens.

ImmunoGen plans to ask the FDA for full approval and file Elahere with European regulators in the second half of 2023.

But despite a spectacular win in platinum-resistant ovarian cancer, the SVB team struck a cautious note on Elahere’s long-term commercial potential. The analysts still believe that the ImmuoGen ADC has a low chance of succeeding in platinum-sensitive ovarian cancer.

Looking forward, it will also be worthwhile to see how the drug performed in the 55% of trial patients who had previously received a PARP inhibitor such as AstraZeneca and Merck’s Lynparza.

Meanwhile, ImmunoGen is testing Elahere as a monotherapy in the phase 2 PICCOLO study in FRα-high, recurrent platinum-sensitive ovarian cancer after at least two prior lines of therapy. The phase 3 GLORIOSA trial is pairing Elahere with Avastin as a maintenance therapy.