Purpose: The anti-HER-2/neu monoclonal antibody trastuzumab has been shown to engage both activatory (fragment C receptor [Fc gamma R]IIIa; Fc gamma RIIa) and inhibitory (Fc gamma RIIb) antibody receptors and Fc gamma R polymorphisms have been identified that may affect the antibody-dependent cell-mediated cytotoxicity (ADCC) of natural-killer cells/monocytes. In this study, we tested whether Fc gamma R polymorphisms are associated with clinical outcome of patients with breast cancer who received trastuzumab.
Patients and methods: Fifty-four consecutive patients with HER-2/neu-amplified breast cancer receiving trastuzumab plus taxane for metastatic disease were evaluated for genotype for the Fc gamma RIIIa-158 valine(V)/phenylalanine(F), Fc gamma RIIa-131 histidine(H)/arginine(R), and Fc gamma RIIb-232 isoleucine(I)/threonine(T) polymorphisms. Trastuzumab-mediated ADCC of patients' peripheral blood mononuclear cells (PBMCs) was measured by chromium-51 release using a HER-2/neu-expressing human breast cancer cell line as a target. Controls comprised thirty-four patients treated with taxane alone.
Results: Our population was in Hardy-Weinberg equilibrium except for the Fc gamma RIIb polymorphism. The Fc gamma RIIIa-158 V/V genotype was significantly correlated with objective response rate (ORR) and progression-free survival (PFS). Also, there was trend significance in ORR and PFS for the Fc gamma RIIa-131 H/H genotype. The combination of the two favorable genotypes (VV and/or H/H) was independently associated with better ORR and PFS compared with the other combinations. The ADCC analysis showed that V/V and/or H/H PBMCs had a significantly higher trastuzumab-mediated cytotoxicity than PBMCs harboring different genotypes.
Conclusion: These data support for the first time the hypothesis that Fc gamma R-mediated ADCC plays an important role in the clinical effect of trastuzumab. Prospective studies are needed to confirm the role of Fc gamma R polymorphisms in predicting clinical outcome of patients with breast cancer treated with trastuzumab-based therapy.