UPDATE 2-Amgen's Vectibix cancer drug shows mixed results

* Says drug fails to prolong overall survival

* Says delays symptom progression in one patient group

* Amgen shares fall 1 percent after-hours (Adds analyst comment, byline; updates shares)

By Ransdell Pierson

NEW YORK, Aug 17 (Reuters) - Amgen Inc (AMGN.O) said on Monday its experimental drug Vectibix failed a primary goal of prolonging survival in a late-stage study of patients with advanced colorectal cancer who had failed to adequately benefit from prior treatments.

Although there was a numerical trend toward prolonging overall survival, the trend did not reach statistical significance, said Amgen, whose shares fell 1 percent in after-hours trading.

But Amgen said the drug, when combined with a standard chemotherapy regimen called FOLFIRI, met another primary goal of significantly delaying a worsening of symptoms among patients that did survive and who had wild-type -- or unmutated forms -- of a protein called KRAS.

The addition of Vectibix (panitumumab) to FOLFIRI did not have any positive or negative effect on delaying symptoms or overall survival among patients whose tumors harbored mutated forms of KRAS, Amgen said in a release.

Amgen noted that earlier trials of Vectibix showed it was able to delay a worsening of symptoms in patients with unmutated forms of KRAS who had not previously been treated for colorectal cancer.

"With these data, Vectibix has now demonstrated improved progression-free survival in Phase 3 trials with KRAS wild-type tumors in both first- and second-line treatment of metastatic colorectal cancer," Amgen said in a release.

JP Morgan analyst Geoffrey Meacham late on Monday reaffirmed his "overweight" rating on Amgen. He said the new data, although mixed, improve the odds that Vectibix will be approved for patients who have failed to benefit from earlier treatment.

"We think the improvement in progression free survival and numerical improvement in overall survival should be adequate" to win approval to designate use of the drug for second-line treatment, he said in a research report.

Moreover, Meacham said the new data -- by supporting second-line use of the medicine -- should prompt Wall Street to boost potential sales estimates for the product.

Amgen said results of the new trial bolster growing evidence that KRAS status -- knowing whether a patient's protein is mutated -- can be a predictive biomarker of how well treatment might work in individual patients.

Studies performed over the past 25 years indicate the KRAS protein plays a big role in regulation of cell growth, Amgen said.

Amgen shares were trading at $59.28 in after-hours activity, from their closing price of $59.84 Monday on the Nasdaq. (Reporting by Ransdell Pierson and Lewis Krauskopf; Editing Bernard Orr and Richard Chang)