Metastatic breast carcinoma in pleural fluid: Correlation of receptor and HER2 status with the primary carcinoma-a pilot study.

Background: Documenting the four molecular subtypes of breast carcinoma is significant as they determine response to therapy, disease free interval and survival. Our aim was to document the subtypes defined by immunohistochemistry (IHC) expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2): namely ER + PR+ HER2+; ER + PR + HER2-; ER-PR-HER2+; and ER-PR-HER2- in metastatic breast carcinoma in pleural fluid and compare them with their expression in the primary breast tumor.

Methods: Over a period of 18 months, 13 cases of invasive breast carcinoma with metastases to the pleural cavity were studied for subtypes. ER, PR, and HER2 were determined by IHC in the primary breast tumor and the cell blocks of the pleural fluid with metastatic carcinoma.

Results: Age ranged from 33 to 75 years. The primary tumor was ER + PR + HER2+; ER + PR + HER2-; ER-PR-HER2+ and ER-PR-HER2- in 2,9,0 and two cases, respectively while the metastatic tumor in pleural fluid was ER + PR + HER2+; ER + PR + HER2-; ER-PR- HER2+ and ER-PR-HER2- in 6, 3, 3, and 1, respectively. In five cases there was complete correlation between the primary and metastatic tumor. In 7 cases with HER2- primary tumor the metastases was HER2+. One from ER + PR+ HER2- primary tumor showed triple negative expression in the metastasis.

Conclusions: Determining the molecular subtype in metastatic breast carcinoma is of importance as it affects the management. In our series 63% of metastatic tumors to the pleural fluid became HER2 positive and would thus require appropriate therapy. Diagn. Cytopathol. 2016;44:980-986. © 2016 Wiley Periodicals, Inc.