Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of ImmunoGen (NASDAQ:IMGN) slid almost 17% today, after its earnings report showed a larger-than-expected loss. An underwhelming licensing agreement with Roche (PINK: RHHBY.PK) for a potential breast cancer drug, also contributed to the decline.

So what: ImmunoGen's earnings came in at $4.1 million, but losses of $0.30 per share were $0.06 worse than the analyst consensus. Full-year forecasts still project the same $78 million to $82 million loss that the company originally offered in August.

ImmunoGen and Roche's combination development-stage breast cancer drug, T-DM1, was originally thought to be licensed to Roche at a 5% sales royalty rate. A disclosure filed today reported that the rate begins at 3%, only increasing to 5% if the drug generates over $700 million per year in sales. That prompted analysts to significantly lower their royalty estimates. Joel Sendek of Stifel Nicoulas dropped his estimated range from $2.4 million next year, and up to $176 million in 2018, to $300,000 and $126 million in the same time frame.

Now what: After the drop, ImmunoGen now trades at a new 52-week low, and its market cap has shrunk to less than $1 billion. However, ImmunoGen has four other major development-stage cancer drugs, as well as a few other compounds in various stages of development. A $50 million reduction in high-end potential revenue is, of course, a significant drop in T-DM1's value, so investors will now have to consider whether the company has any other compounds or partnerships in its pipeline that might make up for it.

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