ImClone

(IMCL)

tumbled Thursday after German pharmaceutical firm

Merck KGaA

said it doesn't plan to expand a trial of the cancer drug Erbitux.

Shareholders of ImClone and its Erbitux development partner

Bristol-Myers

(BMY) - Get Report

were evidently hoping an expanded trial by Merck would help U.S. firms get approval for the drug, which has run into problems with the FDA over the composition of previous studies.

Bristol-Myers and ImClone had asked Merck KGaA to raise the patient numbers enrolled in its trial program to around 500 from 300 and to redesign its study on the drug, a Merck KGaA spokesman told

Dow Jones

.

"Any modification of the trials is above and beyond our contractual obligations with ImClone," the spokesman said. "We had discussions with Bristol-Myers and ImClone. All three companies decided that this collaboration is not in the best interest of the companies."

ImClone was down $2.15, or 14%, to $12.90 on Instinet.

Separately, ImClone posted a first-quarter loss of $30 million, or 41 cents a common share, compared with a loss of $1.2 million, or 2 cents a common share, in the year-earlier period.