Role of progesterone receptor status (PR) as predictive factor of pathological complete response (pCR) to neoadjuvant chemotherapy (NACT) in breast cancer (BC) patients (pts)

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637 Background: While estrogen receptor (ER) negativity has been consistently associated to higher pCR rates after NACT in BC, few data regarding the association of PR with pCR has been reported. PR positivity has been related to taxol resistance in in vitro chemosensitivity assays. Our aim was to investigate the putative role of PR in the prediction of pCR in a cohort of BC pts receiving NACT. Methods: Medical reports of all pts receiving NACT and breast surgery between 2004 and 2006 in our institution were reviewed. Baseline clinical and histological features, along with type of preoperative therapy were examined as variables for association with pCR (no invasive tumor in breast and axilla) using univariate and multivariate analyses. Results: 128 pts were included. 73.4% received anthracycline and taxanes (A&Tx) based CT and 9.4% also received trastuzumab (T). PR+ (≥ 10%) was significantly associated with low histological grade (HG), low Ki67 (<10%), HER-2- (Herceptest 0,1,or 2 with FISH-) and ER+ (≥10%). Overall pCR rate was 18.8%. No PR+ patient achieved pCR. In univariate analysis, high HG, ER-, PR-, HER-2-, high Ki67, T therapy, and number of CT cycles were significantly associated with pCR. In multivariate analysis only HER-2 and PR status were statistically significant. Similarly, PR and HER-2 status were independently related to pCR in the subgroup of pts receiving A&Tx (N = 94, 20.2%pCR). In the HER-2- subgroup (n = 89, 9%pCR) only ER independently predicted pCR, while in the HER-2+ subgroup (n = 33, 42.4%pCR, 57.1%pCR with T), both PR- and T therapy were the only predictive factors for pCR in the univariate and multivariate analyses. When the 24 HER-2+ pts treated with A&Tx (23 taxol/1 taxotere) ± T were separately analyzed, only PR retained statistical significance in the multivariate model. Conclusions: In our cohort of BC pts treated with NACT, PR status independently predicts pCR in the whole population as well as in the A&Tx-treated and in the HER-2+ subgroups. In the HER-2+ pts receiving A&Tx ± T PR negativity was the only factor associated with pCR. PR status merits further investigation as a predictive factor for pCR to NACT, in particular in HER-2+ population. No significant financial relationships to disclose.