We assessed whether
progesterone receptor (PgR) and Ki67 in primary
tumors and/or matched
metastases are predictors of clinical benefit from first-line endocrine
therapy (ET) in advanced
breast cancer. We evaluated patients treated at our institute with first-line ET (2002-2011), excluding those receiving concomitant
chemotherapy or
trastuzumab or pretreated with >2 lines of
chemotherapy. A cut-off of 20 % immunostained cells was used for PgR and Ki67. The main endpoint was time-to-progression (
TTP). Groups were compared by the log-rank test and Cox multivariate analysis. In the 135 assessable patients (93 % were receiving an
aromatase inhibitor;
biomarker assessment had been performed on primary
tumors in 77 cases, on
metastases in 23 and on both in 35), median
TTP was 16 months (median follow-up 43 months). The overall discordance rate between primary
tumors and
metastases was 23 % for Ki67 and 31 % for PgR. A longer median
TTP (24 vs. 12 months, P = 0.012) was seen for PgR >20 % in
metastases. Ki67 showed a trend for
TTP prediction in the entire case series (P = 0.062). Patients with high Ki67 and low PgR in
metastases had a median
TTP of only 5 months. High Ki67 in primary
tumors (P = 0.026) or
metastases (P = 0.01) predicted
disease progression at the first evaluation. PgR in
metastases remained a significant independent predictor of
TTP at multivariate analysis (HR 2.45). In an ER-high population, PgR >20 % in
metastases identified patients with a long
TTP on endocrine treatment, while Ki67 >20 % was associated with an increased risk of non-response.