Jan 28 (Reuters) - Pfizer Inc reported better than expected fourth-quarter results, helped by sales of new treatments for cancer, nerve pain and arthritis. The biggest U.S. drugmaker on Tuesday said it earned $2.57 billion, or 40 cents per share, in the fourth quarter. That compared with $6.32 billion, or 86 cents per share, in the year-earlier quarter, when the company recorded a gain from selling its nutritional products business to Swiss food group Nestle SA. Excluding special items, Pfizer earned 56 cents per share. Analysts, on average, expected 52 cents per share, according to Thomson Reuters I/B/E/S.