Immunoglobulin G fragment C receptor polymorphisms and response to trastuzumab-based treatment in patients with HER-2/neu-positive metastatic breast cancer

Abstract

13090 Background: A potential mechanism of action of the humanized anti-HER-2/neu monoclonal antibody Trastuzumab involves antibody-dependent cellular cytotoxicity (ADCC) with the activation of immune effector cells via their immunoglobulin G fragment C receptors (FcγRs). Trastuzumab has been shown to engage both activation (FcγRIIIa; FcγRIIa) and inhibitory (FcγRIIb) antibody receptors on myeloid cells and several FcγR polymorphisms have been identified that may affect the antibody-dependent cytotoxicity of natural killer cells and macrophages. Methods: Forty consecutive HER-2/neu-positive (FISH+) metastatic breast cancer patients receiving a trastuzumab-based treatment (combined with paclitaxel for the majority) were examined for the FcγRIIIa 158 valine (V)/phenylalanine (F), FcγRIIa 131 histidine (H)/arginine (R), and FcγRIIb 232 isoleucine (I)/threonine (T) polymorphisms. A PCR-RFLP based assay using genomic DNA was performed for FcγRIIIa and FcγRIIa genotyping, while PCR-SSCP methods using complementary DNA were utilized for FcγRIIb. Patients’ peripheral blood mononuclear cells were drawn before treatment initiation and their trastuzumab-mediated killing function was measured by 51Cr release using a HER-2/neu-expressing human breast cancer cell line as a target. The results were then correlated with clinical outcome of these patients. Results: Median age was 60 years (range 26–83 years). Thirty-six (90%) patients received a trastuzumab-based treatment as first-line therapy. The overall clinical benefit rate (CR+PR+SD) was 65% (95% Confidence Interval: 62–71%), including 8 (20%) complete and 11 (27.5%) partial responses. Median survival was 22.3 mo with a median PFS of 7 mo. Trastuzumab-based treatment was well tolerated and no changes in cardiac function were observed. Conclusions: This study evaluates for the first time the potential role of FcγR polymorphisms in predicting response to trastuzumab-based treatment. Results according to this study purpose will be presented at the meeting. No significant financial relationships to disclose.