ImClone Systems Inc., which is trying to capitalize on optimism over its C225 monoclonal antibody to float a 2.5 million share follow-on, revealed an unpleasant surprise last week that caused jittery investors to shave 11 percent off the company's value. The disclosure spawned worries that a patent issued last year to Genentech Inc. (DNA) could block development of C225, a MAb against the EGF receptor that is in Phase III testing in combination with chemotherapy and radiotherapy to treat advanced squamous cell head and neck cancer.