Snapshot A 62-year-old women presents to her primary care physician with a mass in the right breast, which she believes was the result of trauma. On exam there is a firm, fixed 1 cm mass in the right breast in the upper outer quandrant. There is no axillary lyphadenopathy. Introduction Overview a non-invasive lesion due to proliferative changes within the breast lobule not a premalignant lesion considered a risk factor for breast cancer if untreated LCIS will become invasive in 20-30% of patients over a prolonged period of time (10-15 years) 7-11x higher risk of developing invasive breast cancer in a patient with LCIS contralateral cancer can either be ductal or lobular majority are estrogen and progesterone positive Epidemiology Incidence ~10% of "malignant" lesions on mammogram lifetime risk is 1% per year Risk factors age > 40 years family history of breast cancer hormone replacement therapy ETIOLOGY Genetics mutations LCIS cells are usually estrogen/progesterone receptor-positive and HER2/neu-negative Presentation Symptoms asymptomatic breast lump Physical exam breast lump may be detected on exam or may not be palpable Imaging Mammography indications screening regular screening for all women ≥ 40-50 years of age screening of contralateral breast in LCIS patients LCIS often bilateral in the same quadrant need to do mammography of the contralateral breast at regular intervals diagnosis of breast lump findings LCIS not readily visible on mammography STUDIES Core needle biopsy indications diagnosis after lump or lesion detected on mammography diagnosis made via histology proliferation of small cells within the breast lobule with small, uniform, oval-shaped nuclei Differential Ductal carcinoma in situ (DCIS) key distinguishing feature histology DCIS will show proliferation of neoplastic epithelial cells within mammary ductal system with no evidence of invasion into surrounding stroma occasional overlap in LCIS and DCIS features immunohistochemical staining used to differentiate DCIS is positive for e-cadherin while LCIS is negative Treatment Medical tamoxifen indications higher-risk patients to reduce future invasive carcinoma risk close follow-up frequent scheduled exams mammographic screening of both breasts Surgical excisional biopsy indications high-risk patients bilateral mastectomy indications to reduce risk of developing invasive carcinoma in ipsilateral or contralateral breast in patients who have family history of premenopausal breast carcinoma Complications Development of invasive carcinoma Prognosis Very good majority of women with LCIS will not develop invasive breast cancer