Biological fact versus technical artifact in ER negative PR positive breast cancer

Estrogen receptor (ER) negative/progesterone receptor (PR) positive is an infrequently reported biological subtype of breast cancer (BC). Various authors have treated its existence doubtfully. To our knowledge, this study is the first within Egypt and the Middle East to investigate this rare subgroup of BC.

This retrospective study included all ER-/PR + BC patients treated in our center from 2016 to 2022. The collected data were coded, processed, and analyzed using IBM SPSS.

The study included 149 patients with ER-/PR + breast cancer. The mean age was 50.3 years (21-83). The mean follow-up interval was 68 months. pT1 represented 20.8% of the cases, pT2 tumors were 50%, pT3 tumors were 16.7%, while pT4 tumors were 5.6%. As regards nodal staging, pN0 were 36.3%, pN1 24.7%, pN2 19.2%, and pN3 19.8%. The main histology of the tumors was infiltrating duct carcinoma (81.2%), followed by lobular carcinoma (8.7%). Weak PR positivity (Allred score < 6) was documented in 92 patients (61.7%). While the remaining patients showed strong PR positivity (scores of 6 or higher), 68% were HER2 receptor-negative. In the follow-up period, 39% of the patients suffered from disease relapse. The mean disease-free survival was 60.8 months, and the mean overall survival was 69.8 months. The nodal status was the only variable that significantly affected disease-free and overall survival in the univariate analysis, while no factor affected survival in the multivariate analysis.

ER-/PR + breast cancer seems to be an underestimated subtype, which is more aggressive than double-positive hormonal receptor breast cancer but less aggressive than double-negative hormonal receptor breast cancer.