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Supplementary Data from Combined Src and Aromatase Inhibition Impairs Human Breast Cancer Growth In vivo and Bypass Pathways Are Activated in AZD0530-Resistant Tumors

Purpose: Antiestrogens are used to treat estrogen receptor (ER)-α-positive breast cancers and cause a p27-dependent G1 arrest. Estrogen-bound ER recruits Src to mediate proteolysis of p27 and drive cell proliferation. Here, we tested the antitumor efficacy of combined Src and aromatase inhibition for ER-positive breast cancer.Experimental Design: Antiproliferative effects of the aromatase inhibitor, anastrozole, and Src inhibitor, AZD0530, alone or in combination were tested in vitro and in vivo on aromatase-transfected MCF-7Arom5 xenografts. Xenografts were analyzed by immunohistochemistry and proteomic analysis to identify potential biomarkers of drug response and resistance.Results: AZD0530 and anastrozole together increased p27 and caused greater G1 cell cycle arrest than either drug alone. AZD0530 monotherapy initially retarded xenograft growth in vivo, but drug resistance rapidly emerged. Combined anastrozole/AZD0530 reduced drug resistance and showed greater antitumor efficacy in vivo with greater Src and epidermal growth factor receptor inhibition and a greater increase in p27 and reduction of Ki-67 than either drug alone, supporting further evaluation of these putative predictors of response to combined Src/aromatase inhibition in vivo. Anastrozole alone stimulated Src activity both in vitro and in vivo. AZD0530-resistant tumors showed activation of bypass pathways including MEK and phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin, raising the possibility that MEK, mammalian target of rapamycin (mTOR), or PI3K inhibitors may augment Src inhibitor efficacy.Conclusions: These data support clinical investigation of anastrozole-AZD0530 therapy for postmenopausal ER-positive breast cancer. Loss of p27 and increased Ki-67 may predict response and further clinical studies should evaluate for activation of bypass pathways including MEK and PI3K pathways during Src inhibitor therapy.

Purpose To investigate the impact of histologic type invasive lobular carcinoma (ILC) versus invasive ductal carcinoma (IDC) on response to primary chemotherapy (PC) and long-term outcome. Patients and Methods The study included 1,034 patients with stage II and III breast cancer who participated in six clinical trials of PC at our institution between 1985 and 2002. One hundred twenty-two patients (12%) had ILC and 912 (88%) had IDC. All patients received anthracycline-based PC, and 346 patients (33.5%) also received a taxane as part of PC. Pathologic complete response (pCR) was defined as no evidence of invasive disease in the breast and axillary lymph nodes. Results The median patient age was 48 years (range, 18 to 79 years). Patients with ILC tended to be older (median age, 53 years v 47 years for patients with IDC) and have more hormone-receptor–positive tumors (92% v 62%; P < .001), lower nuclear grade (nuclear grade 3, 16% v 56%; P < .001), and higher stage at diagnosis (10% v 0% with stage IIIB or IIIC disease; P < .001). Patients with ILC were less likely to have a pCR (3% v 15%; P < .001) and had a larger number of involved axillary lymph nodes (41% v 26% had > 3 involved nodes; P = .001). At a median follow-up time of 70 months, ILC patients tended to have longer recurrence-free survival (P = .004) and overall survival (P = .001). Conclusion ILC is characterized by lower rates of pathologic response to PC but better long-term outcomes compared to IDC. pCR might not be a prognostic indicator for this group of patients.