BCAR1/p130Cas expression in untreated and acquired tamoxifen‐resistant human breast carcinomas

High BCAR1/p130Cas expression in primary breast tumour cytosol predicts a poor chance of response recurrent disease to tamoxifen treatment in patients with oestrogen receptor (ER)–positive breast carcinomas. In this study, we assessed whether BCAR1/p130Cas expression is altered during acquisition of anti‐oestrogen resistance. BCAR1/p130Cas protein was quantitatively measured by chemiluminescent Western blot analysis in the cytosol of 34 predominantly ER+ carcinomas that initially responded to primary tamoxifen treatment and subsequently progressed (n = 22 ) or developed during adjuvant tamoxifen treatment (n = 12) and compared to 54 untreated ER+ human breast carcinomas. We did not detect significant differences in the level of BCAR1/p130Cas protein in untreated and acquired tamoxifen‐resistant carcinomas. Our results indicate that in tumour progression towards tamoxifen resistance, increase of BCAR1/p130Cas may be only one of the molecular mechanisms. Thus, high BCAR1/p130Cas protein levels appear to be a hallmark for intrinsic resistance to tamoxifen in breast carcinomas. Int. J. Cancer 89:465–468, 2000. © 2000 Wiley‐Liss, Inc.