A new study about a form of early-stage breast cancer called ductal carcinoma in situ (D.C.I.S) has left women as confused as ever about how to treat it. Up to 60,000 American women a year are told they have DCIS; most opt to have a lumpectomy or mastectomy, but many women choose to have both breasts removed, even if one breast shows no sign of DCIS. Some cancer experts say the study offers more evidence that we’re over-treating women. Others say DCIS should still be viewed as potentially dangerous and treated aggressively. We look at the latest research and what it means for patients.