Correlation Of High P95her2:Her2 Ratio With Poor Outcome In Two Phase Ii Clinical Trials Of Trastuzumab-Treated Her2-Positive Metastatic Breast Cancer.

603Background: p95HER2 (p95) is a truncated form of HER2 receptor that had been shown to confer resistance to trastuzumab (T) in vitro. However, conflicting clinical results were observed between p95 and outcome in patients treated with T based therapy to date. Given that p95 level often correlates with high HER2 expression level which confers better outcome, we sought to evaluate the correlation between quantitative levels of HER2, p95, and p95:HER2 ratio in NCCTG N0337 (Phase II study of vinorelbine, capecitabine and T) and NCCTG 98-32-52 (Phase II study of weekly versus every-three-week paclitaxel, carboplatin and T). Methods: A total of 91 formalin-fixed, paraffin-embedded patient samples from N0337 and 98-32-52 were analyzed. The HERmark(R) Breast Cancer Assay (Monogram Biosciences, South San Francisco) was used to measure HER2 expression level. p95 expression was measured using the VeraTag(R) technology (Monogram Biosciences) with an antibody specific for the active Met611 carboxy-terminal fragment ...