(Adds FDA, company comments, detail on genetic issue)
By Susan Heavey
WASHINGTON Dec 12 (Reuters) - U.S. health regulators are weighing whether ImClone Systems and Amgen Inc (AMGN.O) need to do more to show that patients with a certain type of gene are more likely to be helped by two colon cancer drugs.
Early research has indicated that patients with the normal, so-called "wild type" of a gene known as K-ras respond far better to treatment with ImClone's Erbitux and Amgen's Vectibix than those with a mutated form of the gene.
On Tuesday, the U.S. Food and Drug Administration will seek advice from outside experts on whether some new clinical trial is needed to confirm the findings, or if analyzing data from previous trials, as the companies want to do, is adequate.
The companies would like the FDA to officially recognize the genetic factor so they can add the information to the drugs' labels and discuss the issue with doctors.
While eliminating patients with a mutated K-ras gene from treatment would cut sales of the drugs, the findings could be an advance toward so-called personalized medicine, in which genetic testing can determine who is most likely to benefit from expensive drugs.
ImClone, recently acquired by Eli Lilly and Co (LLY.N), and Bristol-Myers Squibb Co (BMY.N), co-market Erbitux in the United States. Merck KGaA (MRCG.DE) sells the drug, which is also approved to treat head and neck cancers, outside the United States.
Amgen spokeswoman Christine Regan said the company was concerned with making sure that "the right patients take the right drug," not the impact on sales. Knowing who should not take Vectibix would help them avoid side effects and focus on better options, she said.
More than 108,000 U.S. cases of colon cancer were diagnosed and nearly 50,000 died from the disease in 2008, according to the government's National Cancer Institute.
Roughly 60 percent of them have tumors that express the normal K-ras gene, according to Bristol-Myers.
K-ras screening could also help save patients and insurers money. Erbitux costs about $10,000 a month in the United States, while Vectibix cost about $8,000 a month.
Both ImClone and Amgen have proposed retrospective testing of K-ras status from large randomized trials.
"Although this was a retrospective subgroup analysis, it represented one of the largest data sets for the association of K-ras mutation and the role of cetuximab (Erbitux) in combination with chemotherapy," ImClone wrote in documents released by the FDA ahead of Tuesday's meeting.
Other ongoing studies have been designed and have recruited patients or are looking to enroll them, the FDA said. The drugmakers modified the ongoing studies to enroll only patients with the wild type K-ras gene.
Enrollment in two earlier trials for ImClone's Erbitux were halted after the K-ras finding so patients could be informed. Patients are still being sought for another trial that was put on hold, the company said. "It is no longer feasible to conduct clinical trials in patients with MT (mutant) K-ras in their tumors," ImClone wrote.
Some breast cancer treatments have already been reserved for use in patients with a specific genetic makeup. Genentech Inc's DNA.N Herceptin and GlaxoSmithKline Plc's (GSK.L) (GSK.N) Tykerb are approved for the 25 percent to 30 percent of breast cancer patients who are positive for the HER-2 genetic marker.
Amgen shares closed up 1.5 percent at $58.13 on Nasdaq. Lilly shares closed up 2.2 percent at $36.41, and Bristol ended up 4.9 percent at $22.51, both on the New York Stock Exchange. (Additional reporting by Bill Berkrot in New York; Editing by Dave Zimmerman and Tim Dobbyn)