CA125 kinetics as a potential biomarker of prognosis in nivolumab monotherapy for patients with advanced gastric cancer and peritoneal metastasis.

Abstract

445 Background: The ascites develop in large proportion of patients during salvage-line chemotherapy for advanced gastric cancer (AGC). Serum CA125 is reported to be potential biomarker in peritoneal metastasis and associate with prognosis in first-line treatment for AGC. Therefore we aimed to clarify the association between serum CA125 and therapeutic efficacy for AGC treated with third of later-line nivolumab monotherapy (Nivo). Methods: This multicenter retrospective study comprised AGC patients who received Nivo in third line or later setting between Jun. 2015 to May 2019. Patient background and treatment outcome was assessed in CA125 elevated and non-elevated group before Nivo (cut-off, 37 U/ml). The CA125 kinetics after chemotherapy was calculated based on baseline and first measure of CA125. Further, the association between CA125 kinetics and ascites burden during chemotherapy were evaluated based on optimal cut off value calculated receiver operating characteristic (ROC) curve analysis. Results: A total 50 patients from 5 hospitals were assessable. The proportion of poor PS, moderate/severe peritoneal effusion, low albumin was significantly larger in CA125 elevated group (n=29) than those in non-elevated group. The median value of CA125 before Nivo was elevated according to ascites burden (none, 31.0 U/ml; mild, 49.4 U/ml; moderate/severe, 187.0 U/ml; p<0.001). The overall survival was significantly shorter in elevated group than that in non-elevated group (median, 3.2 vs. 9.4 months, p=0.035). After Nivo, first-time measure of CA125 was performed in a median of day 27. The median change of CA125 was correlated with ascites response (CR/PR, 0.04%/day; SD, 2.06%/day; PD, 4.17 %/day, p=0.013). ROC curve analysis showed that the optimal cut-off value of CA125 kinetics for ascites progression was 2.4%/day (specificity 75%, sensitivity 70%). The progression free survival in increased group was significantly shorter than that of non-increased group in patients with peritoneal dissemination (median, 1.4 vs 3.3 months, p=0.016). Conclusions: The serum CA125 before Nivo was associated with ascites burden. Further, CA125 kinetics after Nivo was associated with prognosis in AGC patients with peritoneal dissemination.