MICROSATELLITE INSTABILITY ON THE PROGNOSIS AND EFFICACY TO CHEMOTHERAPY IN GASTRIC CANCER PATIENTS: A PROPENSITY SCORE-MATCHED STUDY
Marina A. Pereira*1,2, Marcus F. Ramos1,2, André R. Dias1,2, Leonardo Cardili1,2, Venâncio A. Alves1,2, Bruno Zilberstein1,2, Evandro S. de Mello1,2, Ulysses Ribeiro1,2
1Universidade de Sao Paulo Faculdade de Medicina, Sao Paulo, São Paulo, Brazil; 2Universidade de Sao Paulo Instituto do Cancer do Estado de Sao Paulo, Sao Paulo, São Paulo, Brazil
Microsatellite instability (MSI) gastric cancer (GC) generally has a better prognosis and no benefit in survival with chemotherapy (CMT) than microsatellite stable (MSS) GC. However, patients with MSI GC have distinct clinicopathological characteristics consisting of factors predicting positive and negative outcomes, such as less lymph node metastasis and older age patients. Therefore, measuring the value of MSI as a prognostic factor after controlling for these discrepant factors is necessary to determine the real impact of MSI/MSS status on survival. Thus, this study aimed to compare the survival of GC with MSI and MSS using Propensity Score Matching (PSM) to reduce the biases of clinicopathological features. We further analyzed the efficacy of CMT in the MSI population.
We reviewed all GC patients who underwent curative gastrectomy. Patients were divided into MSI and MSS groups. PSM including 8 variables (sex, age, comorbidities, ASA, type of gastrectomy pT, pN and CMT) was used to match clinicopathological factors between the two groups.
Among the 378 patients enrolled, 78 (20.6%) had MSI. Older age (p<0.001), subtotal gastrectomy (p=0.008), pN0 (p=0.020), and earlier stage tumors (p=0.012) were associated to MSI GC. Survival analysis showed better disease-free survival (DFS) and overall survival (OS) in the MSI group (p=0.012 and p=0.019, respectively). After PSM, 78 patients were matched in each group. All variables assigned in the score were well matched, and both groups became equivalent regarding age (p=0.741), type of gastrectomy (p=0.510), pT (p=0.744), pN (p=0.336), and pTNM (p=0.244). After the matching, the DFS and OS differences by MSI status were estimated to be larger than before (DFS: 63.3% vs 41.4% p=0.002; OS: 65.8 vs 42.5%, p=0.002). Regarding MSI patients referred for CMT (n:60; stage>IB), 51.7% received CMT (MSI+CMT) and the others were treated with surgery alone (MSI+SURG). There was no difference in DFS and OS between both groups (p=0.255 and p=0.178, respectively). Also, recurrence-free survival was equivalent in MSI+CMT and MSI+SURG groups (72.1% vs 66.9%, p=0.638). Survival analyses demonstrate that DFS and OS of MSI+SURG were similar to MSS GC who received CMT (p=0.869 and p=0.706, respectively).
1.Even after controlling for clinicopathological characteristics, MSI was a strong prognostic factor. 2. MSI GC showed no significant survival benefit with the addition of CMT.
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