65P - Serum HER-2 Levels as a Predictor of Clinical Outcome in Metastatic Breast Cancer (MBC) Patients Treated with Trastuzumab-Based Therapies

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Introduction: The extracellular domain of the HER-2 is shed by cancer cells and can be reproducibly and accurately measured in serum. An elevated serum HER-2 (sHER-2) level is considered >15 ng/ml. In studies of patients treated with hormone therapy, chemotherapy or combinations, sHER-2 levels continuously > 15 ng/ml for the entire course of disease had a significantly worse overall survival (OS) compared to patients whose serum HER-2/neu levels were continuously < 15 ng/ml. In our study, we monitored sHER-2 levels in patients who received trastuzumab together with chemotherapy to see if sHER-2 levels above or below 15ng/ml were reflective of clinical outcomes. Methods: This study was a pooled analysis of 307 MBC patients from 7 institutions who received first line trastuzumab based therapy. The baseline (BL) sample was collected prior to trastuzumab therapy and a follow-up sample was collected 16-120 days after start of therapy. Results: Group 1 consisted of 156 patients who had BL sHER-2 levels >15 ng/ml and at first follow-up (16-120 days) continued to have sHER-2 levels >15 ng/ml. The median time to progression (TTP) was 224 days. Group 2 consisted of 147 patients who had either BL samples of > 15 ng/ml or < 15 ng/ml. In group 2, if sHER-2 stayed < 15ng/ml or dropped to < 15ng/ml at first follow-up, the median TTP was significantly (p = 0.003) higher at 334 days. In the 121 MBC patients who started out > 15ng/ml at BL and who remained > 15ng/ml at first follow-up had a median survival of 618 days. The 111 patients who had a BL value of > 15 ng/ml or < 15ng/ml and who either remained < 15ng/ml or dropped < than 15ng/ml had significantly (p = 0.003) longer median survival of 1030 days. Conclusions: In this study, we found that those who had > 15 ng/ml sHER-2 levels at BL and > 15ng/ml at first follow-up had a significantly shorter median TTP and a significantly shorter median OS. In contrast, patients with a decrease to <15ng/ml or who maintain sHER-2 levels < 15 ng/ml had a significantly longer median TTP and longer median OS. Increasing sHER-2 levels in patients was an early indicator of progression and patients with persistently high levels >15ng/ml had a significantly shorter median TTP or shorter median OS. Disclosure: W.P. Carney: I am employed by the company that manufactures the product discessed in the abstract. I do not have any stock interest in the company. All other authors have declared no conflicts of interest.