Crunch time for ImmunoGen as phase 3 readout looms for lead ADC

Analysts say ImmunoGen could make $1 billion from the drug at peak assuming a 2020 launch (Agê Barros via Unsplash)

2019 could be a pivotal year for antibody-drug conjugate specialist ImmunoGen as it tries to draw a line under past challenges with phase 3 data for lead drug mirvetuximab soravtansine.

Within the next few months, ImmunoGen should report the results of its FORWARD I trial of the wholly owned folate receptor alpha-targeting ADC in platinum-resistant ovarian cancer, which aims to displace chemotherapy as the go-to treatment in these patients.

Analysts at Jefferies say they are “leaning positively on the outcome of the trial”, which could lead to an FDA approval in 2020 and—if all goes to plan—U.S. sales of around $774 million in 2032, with another $233 million possible from ex-U.S. royalties.

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ImmunoGen has one of the longest histories in the biotech sector, having been incorporated way back in 1981, so it has been a long haul towards sustainable revenues and profits for the company’s investors as it approaches the end of its fourth decade of operations.

The last couple years have also been a little mixed for ImmunoGen’s ADC pipeline, with a late-stage failure of Bayer-partnered mesothelioma drug anetumab ravtansine in 2017 and the loss of Sanofi as a partner for its anti-LAMP1 candidate last year. On the plus side, it also signed new partnering deals with Jazz Pharma and Debiopharm.

Jefferies is expecting data from FORWARD I to read out in the first half of the year, and said the trial will give ImmunoGen more than one shot on goal.

The study is comparing mirvetuximab to the most commonly used second-line chemotherapies—Johnson & Johnson’s Doxil (pegylated liposomal doxorubicin), topotecan and paclitaxel—and the best outcome will be a significant improvement in median progression-free survival (mPFS) for the ADC across the whole patient population.

If that doesn’t happen, ImmunoGen could still move ahead with registration if mirvetuximab is shown to be better than the comparators in a subset of patients with high levels of folate receptor alpha (FRα) expression. FRα is overexpressed on ovarian and several other epithelial cancers, and the majority of the FORWARD I cohort are high expressers.

From data generated with the ADC to date, Jefferies think that it has a reasonable chance of showing a two month or more advance on mPFS which should be enough for FDA approval, given that the current second-line chemotherapies typically only extend life for three to four months.

It is worth noting, however, that a couple of other FRα-targeting drugs have failed at the last hurdle in refractory ovarian cancer, including Merck and Endocyte’s vintafolide and Eisai/Morphotek’s farletuzumab.

Nevertheless, ImmunoGen reported positive preliminary results with mirvetuximab and Merck’s PD-1 inhibitor Keytruda (pembrolizumab) at last year’s ESMO which seemed to indicate a benefit for the combination over the ADC alone, which adds to the optimism about the program.

“We see use in combination in earlier lines of therapy as upside to our estimates,” said the Jefferies analysts.

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