Power of PgR expression as a prognostic factor for ER-positive/HER2-negative breast cancer patients at intermediate risk classified by the Ki67 labeling index.

Background: The Ki67 labeling index (LI) is regarded as a significant prognostic marker in ER-positive/HER2-negative breast cancer patients. The expression of PgR has recently been identified as another prognostic marker. In the present study, we investigated the prognostic utilities and most suitable cut-off values for Ki67 and PgR, and evaluated the relationship between Ki67 LI and PgR expression in ER-positive/HER2-negative breast cancer.
Patients and Methods: In the present study, 177 consecutive Japanese women with ER-positive/HER2-negative invasive carcinoma of no special type who were treated between 2000 and 2001 were enrolled. Recurrence-free survival (RFS) and cancer-specific survival (CSS) were analyzed according to Ki67 LI and PgR expression, and significant cut-off values for selecting patients with a poor prognosis were evaluated.
Results: The cut-off values for Ki67 LI as a prognostic marker plotted against P values showed bimodal peaks at 10% and 30%. Among the cut-off points examined for the PgR status, 20% PgR positivity was the most significant for predicting survival differences (RFS: P = 0.0003; CSS: P < 0.0001). A multivariate analysis showed that PgR (≥20%) was an independent prognostic marker (RFS: P = 0.0092; CSS: P = 0.00014). Furthermore, in the intermediate risk group with Ki67 LI of 10-30%, the low PgR <20% group had a markedly poorer prognosis for RFS and CSS (RFS: P < 0.0001; CSS: P < 0.0001).
Conclusions: The expression of PgR is a potent prognostic indicator for evaluating the long-term prognosis of ER-positive/HER2-negative breast cancer, and the most suitable cut-off value was found to be 20%. Furthermore, the PgR status is a powerful method for selecting patients with a poor prognosis among ER-positive/HER2-negative patients at intermediate risk, as assessed using Ki67 LI.