Abstract

BACKGROUND
Micropapillary carcinoma (MPC) is known to have a worse prognosis than the other subtypes of breast cancer. Occasionally, MPC is observed in association with invasive ductal carcinoma not otherwise specified (IDC NOS), as well as mucinous carcinoma.
METHODS
We examined the immunohistochemical expression of an estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2) in 127 cases of surgically resected MPC or IDC NOS with MPC. Further, we classified these cases based on their immunohistochemical profile.
RESULTS
Among the IDC NOS with MPC cases, 47 were luminal A (62.7%), 10 were luminal B (13.3%), and 9 were HER2 (12.0%). The MPC cases included 4 luminal A (50.0%), 2 luminal B (25.0%) and 1 HER2 (12.5%) subtypes. Of the mucinous carcinomas with MPC, 4 were grouped as luminal A (57.1%), 1 as luminal B (14.3%), and 2 as HER2 (28.6%) subtypes. However, among the mucinous carcinomas, 33 were categorized as luminal A (89.2%), 3 as luminal B (8.1%), and 1 as HER2 (2.7%) subtype, indicating a low incidence of HER2 subtype as compared to the other subtypes.
CONCLUSIONS
The luminal B and HER2 subtypes were prevalent in carcinomas with MPC. This result explains the poor prognosis of breast carcinomas with an MPC pattern.

• Keywords: Breast carcinoma;Immunohistochemistry;HER2;Micropapillary carcinoma;