Antibody-dependent cell-mediated cytotoxicity (ADCC) evolution under treatment by cetuximab and links with treatment outcome in colorectal cancer (CRC) patients.

2600 Background: ADCC plays a role in antitumor activity of IgG1 mAb by inducing immune cell-mediated lysis of tumor cells. We evaluated ADCC ability before and under cetuximab-based treatment and examined its impact on treatment outcome. Methods: 29 patients (17 men, 12 women, median age 72, range 51-84) with metastatic wild-type KRAS CRC treated with chemotherapy (irinotecan or Folfiri) plus cetuximab were prospectively enrolled. ADCC ex-vivo was measured before starting treatment and every 2 months during treatment (1 to 7 measurements/patient, 12 patients with >2 measurements). 400 000 purified Natural Killer cells (CD3- CD56+) from patients were incubated with 10 000 target cells (CAL166 cancer cell line expressing EGFR) and 10 µg/ml cetuximab (triplicates). Cytotoxicity was measured by the LDH-release assay. ADCC was expressed as the % of lyzed target cells. Gene polymorphisms of Fcγ receptors FCGR2a (131Arg>His) and FCGR3a (158Phe>Val) were analyzed (Allelic Discrimination assay). Results: The feas...