Small infiltration of ductal carcinoma in situ suggests that the patient’s pathologic type is ductal carcinoma of the breast and the cancer cells have broken through the basement membrane. Ductal carcinoma in situ generally refers to intraductal carcinoma in situ of the breast, which mostly means that the lesion is confined to the ducts without the possibility of lymph node metastasis. If ductal carcinoma in situ shows infiltration, it means that the cancer cells have broken through the basement membrane and are starting to enter into the ducts, while minimal means that the infiltration degree and scope are not large. At this time, even if the degree of infiltration is not high, it should be treated as invasive cancer. Patients with ductal carcinoma in situ with microscopic infiltration should follow the doctor’s advice to choose appropriate treatment.