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What happened 

Shares of ImmunoGen (NASDAQ:IMGN), a clinical-stage biotechnology company focused on finding cures for cancer with its proprietary antibody-drug conjugate platform, were rocketing higher by 29% as of 3 p.m. EST on Friday, apparently eager to ring in the new year with a bang.

So what

Unfortunately, the reason for ImmunoGen's surge higher remains a bit of a mystery. The closest thing to tangible news for ImmunoGen that would have the potential to move the company's stock was a press release this past Wednesday, Dec. 28. The press release was a needed feather in the cap for lead drug candidate mirvetuximab soravtansine (previously known as IMGN 853).

As the release points out, mirvetuximab soravtansine led to an encouraging number of responses and improved progression-free survival (PFS) in folate receptor alpha positive platinum-resistant ovarian cancer patients. The 46-patient phase 1 extension study demonstrated a confirmed response in 26% of patients. Historically, standard single-agent therapy in platinum-resistant ovarian cancer patients is under 20%. Median PFS for all 46 patients was 4.8 months, which compared favorably to the 3.5 to 4 months that's typical of current single-agent therapies.

However, one subgroup stood out. Patients with one to three prior lines of therapy and medium to high folate receptor alpha expression exhibited a 44% overall response rate and a median PFS of 6.7 months. ImmunoGen is designing its pivotal phase 3 FORWARD I study around this subgroup.

Now what

Sometimes, the stock market does funny things, and today appears to be one of those days. This news came out two days prior, yet ImmunoGen's shares hardly budged then. Today, they can't be contained. This is a good reminder that day-to-day market moves simply can't be predicted, so we, as investors, should stick to what we do best: examining how the bigger picture will affect our investment theses.

When it comes to ImmunoGen, that investment thesis revolves around mirvetuximab soravtansine, though for now it's a bit of a waiting game until FORWARD I data is available. There are certain to be other catalysts in 2017, including the first clinical data for IMGN 779, a CD-33-targeting antibody-drug conjugate for acute myeloid leukemia patients. But at the end of the day, investors are going to want to be paying closest attention to ImmunoGen's lead drug.

Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong. The Motley Fool recommends ImmunoGen. The Motley Fool has a disclosure policy.