Implications For Restaging In Gastric Cancer With Peritoneal Metastasis Based On The 15th Japanese Classification Of Gastric Carcinoma

Background and purpose: For gastric cancer with peritoneal metastasis(GCPM)patients,there is no universally accepted prognostic staging system.This study aimed to validate the predictive ability of the 15 th peritoneal metastasis staging system(P1abc) of the Japanese Classification of Gastric Carcinoma(JCGC).Methods: The data of 309 GCPM patients from July 2007 to July 2017 were retrospectively analyzed.This study compared the prognosis prediction performances of P1 abc,the previous JCGC PM staging(P123)and Gilly staging systems through C-index,Akaike information criterion(AIC),relative likelihood and likelihood ratio chi-square.Results: Total of 309 GCPM patients were analyzed.The number of P1 a,P1b and P1 c patients was 79,111 and 119,respectively.The median survival time is 8 months(5-16months).The survival curve revealed a significant difference in overall survival(OS)predicted by P1 abc,P123 and Gilly staging(all P<0.05),and the survival of the two adjacent substages were well distinguished by P1 abc but not by P123 and Gilly staging.Both P123 and Gilly staging were substituted with P1 abc staging in a 2-step multivariate analysis.The results showed that P1 abc staging was superior to both P123 and Gilly staging in its discriminatory ability(C-index),predictive accuracy(AIC)and predictive homogeneity(likelihood ratio chi-square).OS was significantly different between patients who did not undergo therapy and those who underwent palliative resection(PR),palliative chemotherapy(PC)and palliative resection combined with palliative chemotherapy(PRCPC)(P<0.001).The OS of patients treated with PRCPC were superior to that of patients treated with PR or PC(P=0.001).A stratified analysis by different therapies indicated that based on the OS of P1 a and P1 b patients,PRCPC was superior to PR and PC(P<0.05),while the OS of patients treated with PC was similar to that of patients treated with PR or PRCPC in both the P1 a and P1 b substages(P>0.05).Further analysis of P1 c patients showed that patients treated with PRCPC had a similar OS as those treated with PR or PC(P=0.505),but patients treated with PC had a significantly better prognosis than those treated with PRCPC or PR(P=0.021).Conclusion: P1 abc staging is superior to P123 and Gilly staging in predicting the survival of GCPM patients.Surgeons can provide these patients with appropriate treatment options according to the corresponding substages within P1abc.