507PDPOSEIDON PHASE I/II TRIAL: ABITUZUMAB COMBINED WITH CETUXIMAB PLUS IRINOTECAN AS SECOND-LINE TREATMENT FOR PATIENTS WITH KRAS WILD-TYPE METASTATIC COLORECTAL CANCER

response rates (RRs) were 27.4%, 25.4%, and 26.4%, respectively. Grade ≥3 treatment-emergent adverse events (TEAEs) were observed in 72%, 78%, and 67% of pts in Arms A, B, and C, respectively, and 13%, 10%, and 8% of TEAEs resulted in death (none considered abituzumab related). High integrin αvβ6 expression in the tumor tissue (98/197 analyzed pts) was associated with longer OS (HR, 0.48 [95% CI, 0.28, 0.82]) and better RR (31% vs 16%) for abituzumab-treated pts vs SoC. Additional data on circulating plasma proteins as candidate biomarkers and pharmacokinetics will be presented. Conclusions: Although no difference in PFS was observed with the addition of abituzumab to SoC, abituzumab did prolong OS and doubled RR in pts with high tumor expression of αvβ6. The overall safety profile of abituzumab combined with SoC was acceptable.