[Clinicopathologic study of infiltrating epitheliosis of the breast].

Objective: To evaluate the morphological and immunohistochemical features of infiltrating epitheliosis and its differential diagnosis. Methods: Nine consultation and routine cases of infiltrating epitheliosis diagnosed from January 2015 to December 2016 in Fudan University Shanghai Cancer Center were collected. All tissues were formalin-fixed paraffin-embedded and routinely HE stained. The HE slides were reviewed. Immunohistochemical staining of CKpan, CK7, CK19, CK5/6, CK14, p63, SMMHC, Calponin, ER, PR, HER2, Ki-67 and S-100 protein was performed using Ventana BenchMark automated immunostainer. Results: The morphological features of infiltrating epitheliosis included: (1) Florid proliferation of epithelial cells forming solid nests or papillary, glandular and cord-like pattern. The proliferative cells possessed nuclei of varying size and shape without atypia. (2) The stroma was altered, showing varying degrees of fibrosis or sclerosis. (3) The proliferative epithelial nests might flow into the spaces within small ducts and lobules at the periphery of the lesion, resulting in pseudo-infiltration. Immunohistochemically, infiltrating epitheliosis was non-uniformly positive for ER/PR, and was positive for high molecular weight CK5/6 and CK14. Myoepithelial markers p63, SMMHC and Calponin demonstrated intact, partial or entire loss of myoepithelial cells around the epithelial nests. The loss of myoepithelial markers staining was more frequent at the periphery of the lesion. The most important differential diagnoses included invasive ductal carcinoma, ductal carcinoma in situ (DCIS), and low grade adenosquamous carcinoma, etc. Conclusions: Infiltrating epitheliosis is an important pseudo-infiltrating lesion. The lack of atypia, non-uniform ER/PR expression, positivity for high molecular weight cytokeratins, and the intact to partial to entire loss of myoepithelial markers around the proliferating cell nests are the key points to differentiate it from invasive carcinomas and DCIS.