Progesterone receptor status provides predictive value for adjuvant endocrine therapy in older estrogen receptor-positive breast cancer patients

Estrogen receptor (ER) status can predict the efficacy of endocrine therapy. However, the predictive significance of the progesterone receptor (PgR) is controversial in an adjuvant setting. Records of 758 ER+ breast cancer patients who received adjuvant tamoxifen (TAM) for 3–5 years were reviewed to evaluate the predictive value of PgR for TAM treatment in ER+/PgR+ and ER+/PgR− groups. By a median of 40 months’ follow-up, there was no significant difference between the two groups with regard to disease-free-survival (DFS). On the basis of STEPP analysis showing the tendency of age effect on DFS in both the ER+/PgR− and ER+/PgR+ groups, we classified the ER+ patients into three strata by age (<45, 45–60, andgreater-or-equal, slanted60 years). There was no significant difference in DFS and overall survival (OS) between the two groups in the <45 stratum and the 45–60 stratum. In contrast, the ER+/PgR− group had a worse prognosis in the greater-or-equal, slanted60 stratum with regard to both DFS (P=0.0484) and OS (P=0.0009). The results suggest that PgR status might be a predictive factor of benefit to be gained from adjuvant TAM for older ER+ patients with regard to DFS and OS. This should take into account older ER+/PgR− patients who tend to be resistant to TAM.