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#6073 Background: Antibody-dependent cell-mediated cytotoxicity (ADCC) may be involved in antitumor effect of therapeutic monoclonal antibodies and their effector functions are induced following the interactions of IgG with FcGR. Studies have shown that FcGRIIIa-V158F and FcGRIIa-H131R polymorphisms may predict response to retuximab, cetuximab in patients with follicular lymphoma, colorectal cancer, and recently, trastuzumab-combined chemotherapy in breast cancer patients (J Clin Oncol 25; 1789, 2008). We tested the hypothesis of whether these two polymorphisms are associated with clinical outcome in metastatic breast cancer patients treated with single-agent trastuzumab treatment.
 Patients and Methods: Patients with HER2-positive (HercepTest (3+) or (2+) with gene amplification either in primary or metastatic site) metastatic breast cancer were enrolled onto this prospective study. Eligible patients were hormone receptor negative or endocrine therapy resistant, and had received no prior chemotherapy for metastatic disease. Study patients received single agent trastuzumab at a loading dose of 4 mg/kg followed by 2 mg/kg per week until disease progression. The first clinical response was assessed at 8 week. FcGRIIIA-V158F and FcGRIIA-H131R genotypes were assessed from genomic DNA extracted from peripheral blood samples. The present study has been approved by the institutional review boards of National Cancer Center and Shikoku Cancer Center Hospital and all registered patients have given written consent to participate in this study.
 Results: To date, 33 patients have been enrolled. The frequency of FcGRIIIa-V158F genotypes were V/V 48%, V/F45%, F/F 6%, and that of FcGRIIA-H131R genotypes were H/H 59%, H/R38%, R/R 3% , respectively. 8-wk response could be evaluated in 29 patients (CR 1, PR 4, SD 13, PD 11). Clinical benefit was observed in 13 patients (CR 1, PR 6, SD>6months 6). FcGRIIIa-158V/V genotype was significantly correlated with 8-wk response (p=.017) and clinical benefit (p=0.02) of single-agent trastuzumab, while there was no significant difference in clinical response to trastuzumab by FcGRIIA-H131R polymorphism.
 Conclusion: Although still preliminary, these data support the previous finding that FcGRIIIa-V158F polymorphisms play an important role in the clinical activity of trastuzumab. Updated results will be presented at the 31st annual San Antonio Breast Cancer Symposium. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6073.

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Hormone receptor and human epidermal growth factor receptor 2 (HER2) protein tests in metastatic breast cancer tissue are recommended in the guidelines of the American Society of Clinical Oncology/American Pathology Association. As part of a multi-institutional study by the National Hospital Organization, we conducted an investigation to examine these molecular markers, using cytological specimens as a substitute for tissue specimens from breast cancer metastasis. To confirm the usefulness of receptors tested in metastatic lesions, the treatment course of registered metastatic breast cancer patients was analyzed. During the April 2015 to March 2016 registration period, there were 62 registrations. Types of metastatic lesions include pleural fluid (44 samples), ascites (14 samples), lymph nodes (2 samples), pericardial fluid (1 sample), and dorsal subcutaneous mass (1 sample). A stable test result was obtained by adopting the receptor examination method, using cell block for immunostaining cytological specimens. The discordance rates of estrogen receptor (ER), progesterone receptor (PR), and HER2 protein expression were 18.2% (95% confidence interval (CI): 7.9–28.8%), 36.4% (95% CI: 23.7–49.1%), and 8.2% (95% CI: 0.1–16.3%), respectively, between the primary tumor and metastatic lesion. Patients who changed from primary negative to metastatic positive ER status had taken a significantly longer time for metastatic foci to appear. Patients with positive ER status in metastatic lesions had significantly better prognosis than ER-negative cases (P = 0.030) by the Log-Rank test. The ER status of the metastatic lesion and the metastatic site were independent prognostic factors by Cox multivariate analysis. Receptor examination with cytological specimens in metastatic lesions has been useful as it provides guidance for the treatment of metastatic breast cancer.

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