Competition from a new Amgen drug has eroded sales of ImClone Systems’ sole product, cancer drug Erbitux.ImClone said US revenue from Erbitux rose 38% to $167.2 million in the fourth quarter, missing the $180 million average analysts’ estimate, according to Bloomberg. Net income grew to $46.6 million, or 53 cents a share from $694,000, or 1 cent, a year earlier.Analysts said the introduction of Amgen’s colon cancer drug Vectibix in October affected Erbitux’s gains and may further chip away at revenue. Erbitux, approved in 2004 to treat refractory colon cancer, benefited after the FDA in March expanded its label to include head and neck cancers.Vectibix is not yet approved for that tumor type but is priced 20% lower than Erbitux at roughly $8,000/month. In its first quarter on the market, the drug posted $39 million in sales, Amgen said. Vectibix represents Amgen’s first foray into therapeutic cancer treatments. Among its older products are the top-selling anemia drugs Epogen and Aranesp, which combined accounted for 47% of the biotech’s $3.84 billion in total revenue, notes Bloomberg. The drugs are facing possible competition from Roche Holding’s Mircera this year.Revenue from Enbrel, for rheumatoid arthritis and other autoimmune diseases, rose 18% to $792 million. The company has said it isn’t satisfied with Enbrel sales among patients with moderate to severe psoriasis and plans a TV ad campaign to boost sales.Amgen said net income climbed to $833 million, or 71 cents a share, from $824 million, or 66 cents, a year earlier. Earnings excluding certain items were 90 cents a share, missing the 93-cent average estimate of 24 analysts surveyed by Bloomberg.