The Breast

Breast imaging has become the main tool in breast cancer screening, diagnosis, and staging. Interventional radiologists and cytopathologists may obtain samples for pathologic evaluation of palpable and non-palpable, but ultrasound (US)-visible lesions. However, the cytopathologist is more likely to obtain adequate FNA cytology samples under US guidance (USG-FNA), a minimally invasive and cost-effective technique that avoids a more costly core needle biopsy for a potentially benign condition. This chapter covers the normal breast, selected inflammatory/infectious entities, and the various benign and malignant primary breast tumors following the 2019 WHO classification of breast tumors. Diagnostic categorization according to the International Academy of Cytology (IAC) Yokohama System for Reporting Breast FNA Biopsy Cytopathology is also included. A section on molecular pathology and gene expression profile in breast carcinoma is included as preamble to the description of the various types of breast cancer with emphasis in the molecular/immunohistochemical classification. Lymphoid malignancies, tumors of the male breast, and metastases are also included. Histopathology, FNA features, immuno-profile, molecular profile, and US features are included in each breast cancer type. Numerous images of FNA cytology, many performed under US guidance, immunohistochemistry, and US features complement the text.