UPDATE 1-Roche melanoma drug shows promise in study

* Confirmed response seen in 52 pct of patients

* 3 patients with complete response, 66 with partial

* Median progression-free survival of 6.2 months seen

NEW YORK, Nov 4 (Reuters) - More than half of patients experienced significant tumor shrinkage after being treated with an experimental drug for advanced melanoma being developed by Roche ROG.VX and privately held Plexxikon, according to preliminary data from a mid-stage clinical trial.

In the 132-patient study there was a confirmed response rate of 52 percent, with three patients showing no evidence of the deadly, difficult to treat disease following treatment, Plexxikon said.

There were also 66 patients who had a confirmed partial response, which was defined as tumor shrinkage of at least 30 percent.

The drug, known as PLX4032 with a Roche designation of RG7204, demonstrated a median progression-free survival -- or the time it took for the disease to worsen in half the patients -- of 6.2 months. That compares with a historical progression free survival rate of less than two months, researchers said.

The median duration of response was 6.8 months, according to data presented at the International Congress for the Society for Melanoma Research in Sydney, Australia.

Not enough patients in the study had died to assess the drug’s impact on overall survival, Plexxikon said.

PLX4032 belongs to a new class of oral drugs that targets tumor cells with a mutation in a gene called BRAF.

A Phase III clinical trial of the drug is currently enrolling, Plexxikon said. Phase III is typically the final stage of human testing before a new drug is submitted to regulators for an approval decision.

“PLX4032 represents a true paradigm shift in the treatment of melanoma and a real breakthrough in melanoma research,” Dr. Jeffrey Sosman, the study’s principal investigator, said in a statement.

“For the first time, we have the possibility of offering a true personalized medicine targeted to melanoma patients who may benefit most from the treatment,” Sosman said.

Melanoma is the deadliest form of skin cancer and once it returns and spreads after initial treatment there are virtually no effective alternative treatments available.

The Roche/Plexxikon drug and an experimental drug for advanced melanoma being developed by Bristol-Myers Squibb Co BMY.N called ipilimumab are providing the possibility of hope for patients who have previously had few options. (Reporting by Bill Berkrot; editing by Carol Bishpric)