Estrogen receptor status has no prognostic relevance in metaplastic breast carcinoma.

Background: Metaplastic breast carcinoma (MBC) is a rare histologic variant of breast cancer characterized by the presence of glandular and non-glandular components. The prognostic significance of estrogen receptor (ER) status has been scarcely studied in these tumors. We therefore investigated the prognostic relevance of ER status in MBC within our patient population.

Design: We reviewed MBC cases (n = 125) between January 2000 and September 2019. Histologic slides were reviewed for variables including tumor morphology and hormonal status. Additional clinical information was obtained from the electronic medical records.

Results: Of the 125 patients, 15 (12%) had ER positive tumors and 110 (88%) had ER negative tumors. Eleven (73%) ER positive tumors had ER positivity > 10% and 4 (27%) had ER positivity ≤ 10%. ER positive tumors had a smaller median tumor size of 2.5 cm, compared with ER negative tumors with median tumor size 3.05 cm, however this difference was not statistically significant (P = 0.82). There were no statistical differences between ER positive and ER negative tumors in terms of histologic grade (P = 0.34), histologic subtype (P = 0.65), clinical stage (P>0.99) or human epidermal growth factor receptor 2 (HER2) expression (P = 0.29). There was also no difference in overall survival (OS) between ER positive and ER negative metaplastic breast cancers (HR = 0.35, 95% CI, 0.003-2.67, P = 0.39).

Conclusion: Our experience suggests that ER positivity has no prognostic relevance in MBC. Regardless of ER expression status, there were no statistically significant differences in overall survival between ER positive and ER negative MBC.