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Why ImmunoGen Stock Is Crashing Today

By Keith Speights – Updated Apr 9, 2019 at 4:23PM

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The biotech reported a big clinical setback for its lead ovarian cancer candidate.

What happened

Shares of ImmunoGen (IMGN -3.15%) are crashing today, down by 45.9% as of 11:31 a.m. EST, after the biotech announced disappointing news from its Forward I phase 3 clinical study evaluating mirvetuximab soravtansine in treating ovarian cancer.

ImmunoGen reported that mirvetuximab soravtansine failed to meet the study's primary endpoint of progression-free survival (PFS) in either the entire group of enrolled patients or in the prespecified subset of patients with high folate receptor alpha expression. The clinical study had enrolled patients with platinum-resistant ovarian cancer that expressed medium or high levels of folate receptor alpha who had been treated with up to three prior therapies.

Businessman looking at red line plunging through floor

Image source: Getty Images.

So what

Investors had been very nervous about the Forward I study results. ImmunoGen's share price tumbled more than 20% on Wednesday as some investors braced for bad news. But just how bad was the news? Pretty bad -- but there was at least a glimmer of hope.

The broad group of patients in the study who received mirvetuximab soravtansine didn't experience a significant difference in PFS or overall survival compared to patients who were only on chemotherapy. But PFS and overall survival periods were longer in the subset of patients with high folate receptor alpha expression who took ImmunoGen's drug than in the group of patients on chemotherapy. A higher confirmed overall response rate was also observed in the subset of patients who took mirvetuximab soravtansine.

However, the problem was that for the results in the subset of patients with high folate receptor alpha expression to be statistically significant, the p-value (a measure of the calculated probability that a hypothesis is true) had to be less than or equal to 0.025 if the p-value in the entire study populated topped 0.05.

All of this statistics talk might be a little confusing, but in a nutshell the fact that mirvetuximab soravtansine wasn't clearly better than chemotherapy in the larger patient group meant that the hurdle was higher for the drug in treating the smaller subset of patients. And that hurdle wasn't cleared.

Click here for the latest earnings call transcript for ImmunoGen.

Now what

ImmunoGen Chief Medical Officer Anna Berkenblit said that the company is conducting additional analyses based on some of the positive efficacy signals that were observed in the Forward study. CEO Mark Enyedy added that ImmunoGen will "further assess the data from Forward I to determine potential next steps with a monotherapy approach."

Probably the best hope for mirvetuximab soravtansine now, though, will be as part of a combination regimen. Enyedy noted that ImmunoGen has generated some encouraging data in combo therapy studies.

The biotech does have three additional antibody-drug conjugates in development. ImmunoGen also has around $295 million in cash to fund operations and advance its candidates. But the future for the company looks much murkier with the latest clinical setback.

Keith Speights has no position in any of the stocks mentioned. The Motley Fool recommends ImmunoGen. The Motley Fool has a disclosure policy.

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