Genentech halted a clinical study yesterday after ovarian cancer patients suffered serious side effects. After the announcement, Genentech's...

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Genentech halted a clinical study yesterday after ovarian cancer patients suffered serious side effects.

After the announcement, Genentech’s shares fell. Avastin, approved for the treatment for colon cancer, was considered Genentech’s most promising drug.

Genentech said it stopped accepting participants in the ovarian cancer study after five of 44 patients suffered bowel tears.

The clinical trial was testing Avastin for ovarian cancer patients whose disease did not respond to chemotherapy drugs containing platinum.

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Jim Reddich, an analyst with Friedman, Billings, Ramsey, said that Avastin might not reach its peak sales potential of $7 billion if doctors became worried about safety. The drug is expected to have sales of $1 billion this year.

Shares of Genentech fell $2.17 to $85.83.