Abstract Microsatellite instability (MSI) has been investigated as a prognostic and predictive factor for chemotherapy in colorectal cancer and has recently been demonstrated to be predictive of the PD‐1/PD‐L1 checkpoint blockade response in various solid tumors. However, MSI status in diffuse large B‐cell lymphomas (DLBCLs) has not been thoroughly explored. This study investigated MSI status in DLBCLs and analyzed the associations between MSI and clinicopathologic characteristics and clinical outcomes. Ninety‐two cases of primary DLBCLs treated with R‐CHOP/CHOP chemotherapy between 2009 and 2017 were collected. MSI detection was performed by the Promega MSI Analysis System. The protein expression of MLH1, MSH2, MSH6, and PMS2 was detected by immunohistochemistry. The associations of MSI‐H and MSI‐L with progression‐free survival (PFS) and overall survival (OS) were assessed by COX models and Kaplan–Meier curves. The correlations of complete response (CR) after R‐CHOP/CHOP chemotherapy with MSI‐H and MSI‐L were examined by univariate and multivariate logistic regression analyses, respectively. 3 of 92 cases (3.2%) were high MSI (MSI‐H), and 9 cases (9/92, 9.8%) exhibited low MSI (MSI‐L). One case with MSI‐H showed negative expression of MSH2 and MSH6. Univariate analysis indicated that MSI‐L was correlated with poor response to R‐CHOP/CHOP chemotherapy in DLBCLs (OR, 0.178; 95% CI, 0.041‐0.776; P = .022). Multivariate analysis showed that MSI‐L was an independent predictive factor for non‐CR to R‐CHOP/CHOP chemotherapy (OR, 0.144; 95% CI, 0.027‐0.761; P = .023). Kaplan‐Meier curves showed that there was a trend that MSI‐H patients had favorable PFS (P = .36) and OS (P = .48), which did not have statistical significance and MSI‐L was not significantly correlated with PFS (P = .24) and OS (P = .52).Our study indicated that there existed MSI‐H and MSI‐L in DLBCLs. MSI‐L could be an independent predictive factor for the chemotherapy response in DLBCLs.
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