CHICAGO (AP) — Only 2 percent of graduating medical students say they plan to work in primary care internal medicine, raising worries about a looming shortage of the first-stop doctors who used to be the backbone of the American medical system. The results of a new survey being published Wednesday suggest more medical students, many of them saddled with debt, are opting for more lucrative specialties. Just 2 percent of nearly 1,200 fourth-year students surveyed planned to work in primary care internal medicine.