A form of breast cancer, which under the microscope can sometimes appear as a benign condition, actually carries a 40-year risk of flaring into invasive cancer with a capacity to spread, medical experts said yesterday.But even with new insight into a type of breast cancer doctors call ductal carcinoma in situ, or DCIS, there is still debate over how to treat it: Do all patients need surgery and radiation, or can some skip them? Physicians Melinda Sanders and David Page of Vanderbilt University Medical Center in Memphis, Tenn., have conducted the largest analysis to date on the form of DCIS known as low-grade, which because of the appearance of the cells can be mistaken for atypical ductal hyperplasia, a benign disorder. Sanders and Page report the results of their research in Cancer, an American Cancer Society publication.