Histomorphology and Immunohistochemical Staining Patterns in Papillary Carcinoma Breast: A Series of 5 Cases

Papillary carcinoma breast is a rare type of breast malignancy accounting for only 0.5% of invasive breast cancers. According to the 2019 WHO Classication of Breast Tumors (5th edition), malignant papillary neoplasms comprise papillary ductal carcinoma in situ (DCIS), encapsulated papillary carcinoma (EPC), solid papillary carcinoma (SPC), and invasive papillary carcinoma (IPC). Histologic features of the tumor include cellular proliferations surrounding brovascular cores, with or without invasion. Conclusive differentiation between benign and malignant papillary breast lesions depends on demonstration of myoepithelial cells which may be difcult to discern on routine H & E stain. Therefore, IHC is a useful adjunct for evaluating the presence and distribution of myoepithelial cells in papillary neoplasms of the breast. Papillary carcinomas of breast are usually manifest the luminal A staining pattern (ER or PR positive; HER2 neu negative) along with negative staining for myoepithelial markers like p63 and calponin. In this case series, we report 5 cases of papillary neoplasms of breast reported at our institution, out of which one was a case of Encapsulated Papillary Carcinoma, while the other 4 were designated as Encapsulated Papillary Carcinoma with Invasion. Coexistent DCIS was seen in 3 cases, but due to the stringent criteria outlined in the latest WHO Classication, none of the tumors qualied to be designated as Invasive Papillary Carcinoma.