NEW YORK (TheStreet) -- Investors are used to seeing mostly positive news on biotech stocks, whether it's big mergers and acquisitions, earnings reports or drug approvals. But that's not always the case, TheStreet's Jim Cramer said on CNBC's "Mad Dash" segment. 

Shares of ImmunoGen (IMGN) - Get Report are down a whopping 48% on Friday, as the company's breast cancer drug didn't quite "pan out," failing Phase 3 trials, said Cramer, the co-manager of the Action Alerts PLUS portfolio

ImmunoGen IMGN data by YCharts

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While there are many high quality biotech stocks, such as Celgene (CELG) - Get Report , Biogen Idec (BIIB) - Get Report , Gilead Sciences (GILD) - Get Report , Regeneron (REGN) - Get Report and Isis Pharmaceuticals (ISIS) , investors need to be aware that there are "downsides" to biotech too, Cramer stressed. Events like drug failures can significantly hurt a company's stock. 

On a more optimistic note, Cramer pointed out that shares of Celgene are higher on positive commentary about the approval of its multiple myeloma drug, Revlimid.

Celgene has "many irons in the fire" and is "a company that has tremendous momentum," he concluded. 

-- Written by Bret Kenwell

Follow @BretKenwell

At the time of publication, Cramer's Action Alerts PLUS had no position in companies mentioned.