PREDICTIVE FACTORS OF ENDOCRINE THERAPY RESPONSE IN BREAST CANCER

Breast Cancer Res Treat. 2015 Jul;152(1):57-65. doi: 10.1007/s10549-015-3423-2. Epub 2015 May 27.

Efficacy of endocrine therapy in relation to progesterone receptor and Ki67 expression in advanced breast cancer.

Rocca A1, Farolfi A, Maltoni R, Carretta E, Melegari E, Ferrario C, Cecconetto L, Sarti S, Schirone A, Fedeli A, Andreis D, Pietri E, Ibrahim T, Montalto E, Amadori D.

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Abstract

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.