Corrected: Some tumors may resist promising Pfizer cancer drug

Corrects 8th paragraph to show Pfizer will file early next year and not later this year for FDA approval

By Gene Emery

BOSTON (Reuters) - A promising cancer pill that could help as many as 5 percent of people with the most common type of lung cancer helps most patients treated but may be vulnerable to resistant tumors, researchers reported on Wednesday.

The Pfizer Inc drug, crizotinib, shrank the tumors of 57 percent of patients and stabilized another 33 percent, Dr. Eunice Kwak of the Massachusetts General Hospital and colleagues reported in the New England Journal of Medicine.

Kwak's team projected that 72 percent of the patients would have enjoyed six months without their disease worsening. Their findings update earlier reports given to various cancer meetings.

"While this is a Phase 1 study, the high response rates observed in patients with ALK-positive (lung cancer) who received crizotinib suggest that we may be one step closer to the development of 'precision' or 'personalized' cancer treatments that target specific genetic factors that drive certain tumors," said Pfizer's Dr. Mace Rothenberg.

But a team of doctors led by Young Lim Choi of the University of Tokyo reported on a patient who developed two independent mutations that made the tumor resistant to crizotinib.

The appearance of resistance is not surprising, Dr. Hiroyuki Mano of the University of Tokyo said in a telephone interview. Other so-called ALK inhibitors have the same problem to some degree.

"The news is both good and bad," said Mano. "It's bad in that there may be some refractory population. But it's good that we know the resistant mutations, so the next generation of ALK inhibitors will use that information to make a less refractory drug in the very near future."

Pfizer said it planned to start submitting data for approval of the drug to the U.S. Food and Drug Administration early next year.

The experimental drug works against cells that have turned cancerous when two genes fuse to form a new gene called EML4-ALK. Although only about 3 percent to 5 percent of people with non-small-cell lung cancer fall into this category, that translates into nearly 10,000 cancer patients in the United States.

Nearly all the volunteers in that study had already undergone one round of treatment with cancer drugs.

Second-round chemotherapy typically only works in about 10 percent of such cases, Bengt Hallberg and Ruth Palmer of Umea University in Sweden said in a Journal commentary.

Side-effects such as nausea and diarrhea were reported to be mild to moderate and seen in 40 percent of patients.

The medical journal also reported that the drug, sometimes designated PF-02341066, helped a 44-year-old man with a rare inflammatory myofibroblastic tumor that had the ALK mutation.

A younger patient without the mutation did not benefit from the treatment, according to a team led by Dr. James Butrynski of the Dana-Farber Cancer Institute in Boston.

Existing cancer pills like AstraZeneca's Iressa and Roche's Tarceva are already known to be effective against cancer in patients with a mutation activating the epidermal growth factor receptor (EGFR).

Lung cancer is the most common cancer killer, with 1.61 million cases worldwide, according to the International Agency for Research on Cancer and it kills 1.2 million of them.

(Editing by Maggie Fox and Jim Marshall)