THOUSAND OAKS, Calif. (AP) — Amgen Inc. said Thursday its cancer drug Vectibix succeeded in a clinical trial, as the study showed the drug was more effective than chemotherapy alone as a primary treatment for colon cancer. The late stage trial compared a combination of Vectibix and a chemotherapy regimen, called Folfox, to chemotherapy alone. Amgen said the patients treated with Vectibix had greater progression-free survival, a measurement of how long they lived until their disease began to advance or spread again. The study tested Vectibix as a primary, or first-line, treatment for the disease. Currently it is only approved as a third-line treatment, meaning Amgen can market it to doctors for patients who have unsuccessfully used two other therapies. Amgen is conducting studies in the hope of gaining approval to market it as a first- and second-line treatment. Amgen said there were 1,183 patients in the trial, and it tested more than 90 percent of the tumors for a mutation on a gene called K-Ras. Worldwide, about 35 percent of colorectal cancer patients have a mutated K-Ras gene, which is associated with more aggressive cancers and lower rates of survival. The other 65 percent of patients have non-mutated, or “wild type,” K-Ras. Full results from the study will be presented at an upcoming medical conference.