WASHINGTON (AP) — Federal health regulators have alerted doctors to a range of side effects, including blistering skin and intestinal problems, seen in patients taking a drug used to treat cancer. The Food and Drug Administration on Friday highlighted new warnings on Tarceva, a daily pill from OSI Pharmaceuticals Inc. and Roche-unit Genentech. The label warns that some patients have experienced gastrointestinal perforation, in which a hole develops in the intestine or stomach. Some other patients developed blistering skin often seen in connection with toxic drug reactions. Some cases of both conditions were fatal, according to the FDA. The labeling advises doctors to discontinue use of the drug if either condition develops. Additionally, the label notes that some patients developed scars and ulcers of the eye while taking the drug. OSI Pharmaceuticals and Genentech notified physicians about the problems in an April letter. Tarceva, has been approved to treat lung and pancreatic cancer. The drug was developed by OSI Pharmaceuticals Inc. and is sold by Genentech. Switzerland-based Roche agreed to buy South San Francisco-based Genentech in March. Shares of OSI Pharmaceuticals Inc. fell 78 cents, or 2.4 percent, to close at $33.59 Friday.