Updated from 3:38 p.m. ESTIs Genta ( GNTA) running into trouble with its highly anticipated cancer drug Genasense? That's the buzz making its way around Wall Street trading rooms over the last week, as word leaked out that the biotech company increased the number of patients in a pivotal, late-stage clinical trial testing Genasense in patients with skin cancer, or melanoma. The buzz turned negative Thursday afternoon, when the company refused to discuss the issue during a conference call. The implications of this resizing -- confirmed by several sources familiar with the trial -- are not clear. Adding patients to a clinical trial in progress can be a red flag, warning of negative results. But it's just as possible that there's nothing wrong whatsoever, and in fact, increasing patient enrollment could be an early tip-off that Genasense is working well. Company officials have so far refused to talk directly to the issue, and that has only added to the mystery. Genta shares fell about 16% on Tuesday and Wednesday as Wall Street biotech traders swapped theories -- mostly negative -- about what was going on with the Genasense study. Thursday morning, Thomas Weisel Partners biotech analyst Patrick Mooney released a note defending Genta, stating that patients have been added to the melanoma trial, but that this was preplanned, approved by the Food and Drug Administration and is a likely positive. (Mooney rates Genta strong buy, and his firm makes a market in the company's stock.) But Genta shares fell sharply lower Thursday afternoon after CEO Ray Warrell refused to answer multiple questions about the trial re-sizing on a conference call sponsored by UBS Warburg. The issue dominated the hour-long call, and the lack of a clear answer clearly spooked investors. Genta closed down $2.61, 16.5% to $13.20. Genta is currently conducting three late-stage clinical trials of Genasense, testing the drug's effectiveness in patients suffering from melanoma and two types of blood cancer -- multiple myeloma and chronic lymphocytic leukemia.