Chapter 23: Breast Pathology

Breast Pathology review of breast pathology details the spectrum of benign and malignant conditions affecting breast tissue, providing critical knowledge for medical board preparation and clinical practice. The discussion begins with inflammatory states, notably acute mastitis, a bacterial infection commonly seen during lactation, and fat necrosis, a trauma-induced condition presenting with calcifications that can clinically mimic malignancy. A significant portion of the chapter focuses on fibrocystic changes, the most frequent benign condition in premenopausal women, which are stratified by cancer risk: nonproliferative changes like simple cysts, fibrosis, and apocrine metaplasia carry no increased risk, while proliferative changes with atypia significantly elevate the probability of developing carcinoma. The summary distinguishes these from benign neoplasms, specifically fibroadenomas, characterized as mobile, rubbery masses in women aged lesser than 35, and phyllodes tumors, leaf-like stromal lesions in older patients that have malignant potential. Intraductal papillomas are identified as the primary cause of bloody nipple discharge. The text then shifts to breast carcinoma, the leading cancer in women, analyzing risk factors such as prolonged estrogen exposure and genetic mutations in BRCA1, BRCA2, and TP53. It traces the progression from preinvasive lesions—differentiating ductal carcinoma in situ (DCIS) from lobular carcinoma in situ (LCIS)—to invasive disease. The major histologic subtypes of invasive cancer are examined, including invasive ductal carcinoma, which forms desmoplastic stroma, invasive lobular carcinoma with its single-file cell pattern, and distinct variants like mucinous, tubular, and medullary carcinomas. Special attention is given to inflammatory carcinoma, a typically aggressive lesion presenting with peau d'orange skin changes due to lymphatic obstruction, and Paget disease of the nipple, defined by intra-epidermal tumor spread. Prognostic factors and therapeutic decisions are outlined based on sentinel lymph node status, tumor grade, and molecular profiling for estrogen and progesterone receptors (ER/PR) as well as HER2/neu overexpression, which indicates susceptibility to trastuzumab. Finally, the chapter addresses male breast pathology, specifically gynecomastia, a benign enlargement resulting from an imbalance between estrogen and androgens caused by physiological factors, cirrhosis, or medications like spironolactone.