P3–047 - Serum HER2ECD Levels in Patients with Advanced Gastric Cancer Treated with Trastuzumab as First-Line Therapy

Abstract

Background: The ToGA study showed that trastuzumab provides a survival benefit in patients with human epidermal growth factor receptor 2 (HER2) positive unresectable or metastatic gastric cancer. Although it has been reported that serum HER2 extracellular domain (HER2ECD) was a useful tumor marker in patients with breast cancer, it remains unknown in patients with advanced gastric cancer. The purpose of this study is to evaluate the efficacy of trastuzumab in combination chemotherapy and usefulness of measurement of HER2ECD levels. Methods: We retrospectively analyzed 12 patients who were treated with first-line trastuzumab in combination of chemotherapy in our hospital. Serum HER2ECD, CEA, and CA19-9 levels at baseline and 1 to 3 months after the initiation of chemotherapy were studied. Results: The patients enrolled in this study included 9 males and 3 females, with a median age of 71 years (range, 59-84). Five patients were in PS of 0, four patients were of 1, three patients of 2. Abnormal serum HER2ECD levels were found in 75%, CEA in 83%, CA19-9 in 67% of the patients. All of three tumor markers showed high levels in six patients. In two patients, CEA and CA19-9 levels were normal, but only serum HER2ECD levels were abnormal. SP (S-1/CDDP) regimen was combined with trastuzumab in 5, XP (capecitabine/CDDP) regimen in 4, S-1 alone in 3 patients. Tumor response was evaluated in 10 patients. Four patients had PR, 5 had SD, 1 had PD, and disease control rate was 90%. Among 9 patients who showed high levels of serum HER2ECD at baseline, 7 patients were evaluated after the initiation of trastuzumab. Serum HER2ECD levels decreased 19% in five patients who had SD. In contrast, it decreased 79% in two patients who had PR. Conclusion: The efficacy of chemotherapies with trastuzumab may correlate serum HER2ECD levels, though it should be evaluated in a larger prospective study.