Association of progesterone receptor status with 21-gene recurrence score and survival among patients with estrogen receptor-positive breast cancer

Progesterone receptor (PR)-negative tumors have been shown to have worse prognosis and were underrepresented in recent trials on patients with estrogen receptor (ER)-positive breast cancer. The role of PR-negative status in the context of 21-gene recurrence score (RS) and nodal staging remains unclear. The National Cancer Database (NCDB) was queried for women diagnosed between 2010 and 2017 with ER-positive, human epidermal growth factor receptor 2 (HER2)-negative, pT1-3N0-1a breast cancer. Logistic and Cox multivariable analyses (MVA) were performed to identify association of PR status with high RS (> 25) and overall survival (OS), respectively. Among 143,828 women, 130,349 (90.6%) and 13,479 (9.4%) patients had PR-positive and PR-negative tumors, respectively. Logistic MVA showed that PR-negative status was associated with higher RS (> 25: aOR 16.15, 95% CI 15.23-17.13). Cox MVA showed that PR-negative status was associated with worse OS (adjusted hazards ratio [aHR] 1.20, 95% CI 1.10-1.31). There was an interaction with nodal staging and chemotherapy (p = 0.049). Subgroup analyses using Cox MVA showed the magnitude of the chemotherapy benefit was greater among those with pN1a, PR-negative tumors than pN1a, PR-positive tumors (PR-positive: aHR 0.57, 95% CI 0.47-0.67; PR-negative: aHR 0.31, 95% CI 0.20-0.47). It was comparable among those with pN0 tumors regardless of PR status (PR-positive: aHR 0.74, 95% CI 0.66-0.82; PR-negative: aHR 0.63, 95% CI 0.51-0.77). PR-negative tumors were independently correlated with higher RS and were associated with greater OS benefits from chemotherapy for pN1a tumors, but not pN0 tumors.