A drug being developed by Pfizer Inc shrank lung cancer tumors in more than half of treated patients, and nearly all showed some benefit, U.S. researchers said on Saturday.

The experimental drug crizotinib is designed to target a specific genetic mutation most commonly found in nonsmokers with non-small cell lung cancer.

“Many of these patients had received three or more prior treatments, and we would expect only about 10 percent to respond. That is why we are so excited about the results,” said Dr. Yung-Jue Bang, the study’s lead investigator, who presented the data at the American Society of Clinical Oncology meeting in Chicago.

The results from the small study were so impressive that the company said it planned to seek U.S. regulatory approval in the first half of next year.

“These results are quite dramatic, and represent an important improvement over what we would see with standard chemotherapy for patients with metastatic disease,” added Bang, professor in the Department of Internal Medicine at Seoul National University College of Medicine in South Korea.

Crizotinib, a pill taken twice a day, works by blocking a genetic mutation that occurs when two genes fuse together to form a gene called EML4-ALK, which causes cancer.

All of the 82 treated patients in the study had the gene mutation and were either nonsmokers or had long given up smoking. Most had already undergone multiple rounds of chemotherapy.

Fifty-seven percent of the treated patients had their tumors shrink at least 30 percent, which was considered a partial response. But 87 percent experienced at least some tumor shrinkage or stable disease after eight weeks, and at least one patient’s tumor disappeared altogether.

Three or four others had no measurable tumor, but could not be characterized as a complete response because of some residual abnormality, such as scarring, Pfizer said.

‘DRAMATIC BENEFIT’

“Patients whose tumors have this mutation ... can expect a dramatic benefit. This is what we as oncologists have always wanted to give our patients,” Dr. Mark Kris, a lung cancer researcher at New York’s Memorial Sloan-Kettering, told reporters at the ASCO meeting.

Many patients also had fewer tumor-related symptoms, such as severe shortness of breath, coughing and severe pain.

“We have seen a number of patients whose symptoms begin to improve within days or weeks of starting therapy,” said Mace Rothenberg, Pfizer oncology’s senior vice president for clinical development and medical affairs, said in a telephone interview.

The most common side effects were nausea and vomiting and were considered to be relatively mild.

On average, the treatment benefits lasted about six months - another encouraging sign since most patients with advanced lung cancer typically live just three or four months.

There was no available data to say whether the drug extended survival.

Although the study was small, the results were so strong that Pfizer has started testing the drug in a late-stage study.

Pfizer has partnered with Abbott Molecular, a unit of Abbott Laboratories, to develop a diagnostic test that looks for the ALK gene mutation.

“We would only administer it to patients who have that mutation, and not to those without it,” Kris said. “That is helpful.”

The company estimates there are about 7,500 to 10,000 patients in the United States with the gene mutation.

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By Julie Steenhuysen and Bill Berkrot

CHICAGO/NEW YORK (Reuters)