UPDATE 2-Tarceva makers warn of liver damage, 2 deaths

(Adds details on study, sales, background)

WASHINGTON, Sept 23 (Reuters) - Genentech Inc DNA.N and OSI Pharmaceuticals (OSIP.O) have alerted doctors about cases of liver damage among patients who took the cancer drug Tarceva in a post-approval study, U.S. regulators said on Tuesday.

One patient died from rapidly progressing liver failure and another died from a liver complication called hepatorenal syndrome, the companies said in a letter to doctors. The study was designed for patients with moderate liver impairment and advanced tumors.

The companies' letter was posted on the FDA's website here#Tarceva.

"Patients with (liver) impairment should be monitored closely during therapy with Tarceva, and dosing should be interrupted or discontinued if changes in liver function are severe," the companies said in the letter.

Global sales of Tarceva hit $866 million in 2007. The drug's generic name is erlotinib.

Tarceva is an oral drug approved for treating certain patients with lung or pancreatic cancer. Most of the 36 patients in the post-approval study had types of tumors that are not approved for treatment with Tarceva, Genentech spokeswoman Charlotte Arnold said.

The prescribing information for Tarceva previously included a "precaution" about liver damage including fatalities. That language has been moved to the stronger "warnings" section of the drug's label, Arnold said.

Roche Holding AG (ROG.VX) owns a majority stake in Genentech and has made an offer for the remaining shares. Genentech has rejected Roche's current offer of $89 a share. (Reporting by Lisa Richwine; Editing by Carol Bishopric and Bernard Orr)