U.S. cancer doctors are worried about their ability to handle an expected surge in cancer cases in the coming years as they face cuts to government health plans and efforts to reduce payments to physicians. The influential American Society of Clinical Oncology, in a report released on Tuesday, cited estimates that cancer will become the leading killer in the United States by 2030 as the population ages, while treatment costs reach new heights. The group is calling on the U.S. Congress to help stabilize payments to doctors under the Medicare insurance program for the elderly.