Characteristics of secretory breast carcinoma with extensive in situ carcinoma components: Clinical and histopathologic analysis

Secretory breast carcinoma is a rare form of breast cancer characterized by low-grade histology, presence of intracellular eosinophilic secretions, and ETV6-NTRK3 fusion. Although several studies have explored the histopathologic features of secretory carcinoma, limited attention has been given to the in situ component. We report 5 cases of secretory breast carcinoma with an extensive intraductal component and describe morphologic and biologic characteristics of the in-situ component of secretory breast carcinoma, along with a detailed review of the literature, and discuss potential diagnostic pitfalls in erroneously identifying the in situ lesion as florid hyperplasia.