Common but diagnostically challenging entities such as papillary lesions and fibroepithelial lesions are discussed in detail, as well as special types of breast cancer including solid papillary carcinoma, lobular lesions and its variants. Uncommon breast lesions such as mesenchymal, lymphoid, and metastatic lesions are also covered. Chapters discuss genetic alterations and molecular abnormalities in breast cancer, and commonly encountered interpretation dilemmas on immunohistochemistry in breast cancer and metastatic cancer to the breast with a focus on prognostic and predictive tumor biomarkers.