The microscope will not be used directly on the participant or in the operating room, but instead will be used to image tissue immediately after excision but prior to the conclusion of surgery. If pathologic examination using NLM concludes that there is invasive cancer or ductal carcinoma in situ (DCIS) at or close to the margin of the specimen, the surgeon will be notified and may decide to do additional surgical shavings before the patient leaves the operating room, in order to improve the likelihood of achieving clean margins and reduce the probability that the patient will be advised to have another operation to achieve clean margins. For both patients on the experimental arm (NLM) and the control arm (without NLM), standard pathologic evaluation of the specimen will be done some days after the lumpectomy is completed. That pathologic evaluation will decide whether or not to recommend that the patient has additional surgery in order to achieve clean margins. The primary outcome measure is the percentage of patients in each group who are advised to have additional surgery for this reason.