UPDATE 1-Amgen says Vectibix colon cancer trial meets goal

* Results apply to patients with normal KRAS

* Details to be presented at medical meeting (Adds background)

LOS ANGELES Aug 6 (Reuters) - Amgen Inc (AMGN.O) said on Thursday colon cancer patients lived significantly longer without their disease getting worse when treated initially with its drug, Vectibix, and chemotherapy, rather than with chemo alone.

The results apply to patients with the normal version of a gene known as KRAS, the company said.

The drug is currently approved only for use in colon cancer patients whose tumors have spread despite chemotherapy.

The latest trial is the first to test Vectibix in patients screened for KRAS type. Previous studies have found that patients with the normal, or wild-type, KRAS gene respond to drugs like Vectibix, which work by blocking epidermal growth factor, while patients with a mutated version of the gene do not respond to the drugs.

"Not only is the improvement in progression-free survival limited to patients with wild-type KRAS tumors, but patients with KRAS mutant tumors were negatively affected when Vectibix was added to a standard chemotherapy regimen," Roger Perlmutter, Amgen's head of research and development, said in a statement.

Vectibix, also known as panitumumab, is in the same class of cancer drugs as Erbitux, or cetuximab, which was developed by ImClone Systems and now sold by Bristol-Myers Squibb Co (BMY.N) and Eli Lilly (LLY.N).

But the Amgen drug has had trouble competing. Sales totaled $153 million last year, compared with more than $1 billion for Erbitux, which is also approved as a treatment for head and neck cancer.

The U.S. Food and Drug Administration last month decided that both drugs could include in their labels information about the KRAS biomarker.

Around 35 percent of colorectal cancer patients are estimated to have KRAS mutations, with the remainder having the normal version of the gene.

Side effects seen in the Amgen study included skin toxicity, low magnesium blood levels and diarrhea, the company said.

Amgen said it will submit the detailed study results for presentation at an upcoming medical meeting.

(Reporting by Deena Beasley; Editing by Richard Chang, Bernard Orr)