The prognostic role of Progesterone receptor (PR) expression in early invasive breast cancer (BC) remains controversial. The aim of this retrospective analysis was to investigate the impact of PR expression levels on outcome of patients with luminal-like Her2 negative early BC.
A population cohort of 441 primary invasive ER+/Her2- early BC patients from a single cancer center underwent surgery and received adjuvant endocrine therapy from 2000 to 2017 was retrieved. To assess the impact of the different PR levels on the prognosis, we calculated the Distant Free Survival (DFS) and the Breast Cancer Specific Survival (BCSS) according to 4 subtypes established on the basis of Ki67 value and PR expression rate (Subtype 1: PR ≥ 20%/Ki67<20%; Subtype 2: PR ≥ 20%/Ki67≥20%; Subtype 3: PR < 20%/Ki67≥20%; Subtype 4: PR < 20%/Ki67<20%). Cox regression analysis was used to correlate tumor characteristics with DFS and BCSS.
The rates of progression disease were 8%, 19%, 30% and 12% in subtype 1, 2, 3 and 4, respectively. Low PR expression (<20%) resulted an independent poor prognostic factor for DFS in patients with high Ki67 value (≥20%). The median DFS was 12.6 months and 10.1 months in subtype 2 and subtype 3, respectively (p = 0.025) (Fig.1). The rates of cancer death were 5%, 12%, 24% and 12 % in subtype 1, 2, 3 and 4, respectively. Consistent with DFS results, a statistically significant correlation of PR expression level and BCSS was reported in patients with high Ki67 index (the median BCSS was 12.9 months in subtype 2 versus 10.5 months in subtype 3, respectively) (p = 0.04). No correlations between survival and PR expression were demonstrated in patients with low Ki67 value (<20%), probably due to the small sample size in the subtypes 1 and 4 groups.
Our study revealed different outcomes among patients with early BC according to different PR expression levels. Noteworthy, in patients with Ki67 ≥20%, low PR expression levels (<20%) could be considered as a prognostic marker suggesting to re-evaluate PR status as a potential therapeutic guide in ER+/Her2- early BC.
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A. Diana: Travel / Accommodation / Expenses: Ipsen, Novartis, Pharmamar, Italfarmaco. F. Carlino: Travel / Accommodation / Expenses: Italfarmaco, Gentili. E. Franzese: Travel / Accommodation / Expenses: Roche. S. Centonze: Travel / Accommodation / Expenses: Thesaro, Roche, Gentili. F. De Vita: Advisory / Consultancy: Roche, Amgen, Celgene, Lilly. F. Ciardiello: Advisory / Consultancy: Merck, Roche, Lilly, Bayer, Amgen, Pfizer, Servier. M. Orditura: Honoraria (self): Epionpharma, Italfarmaco; Travel / Accommodation / Expenses: Roche; Research grant / Funding (institution): EISAI. All other authors have declared no conflicts of interest.