The real-world data on microsatellite instability status in various unresectable or metastatic solid tumors

Microsatellite instability-high (MSI-H) is an important biomarker for predicting the effect of immune-checkpoint inhibitors (ICIs) on advanced solid tumors. MSI-H is detected in various cancers, but its frequency varies by cancer type and stage. Therefore, precise frequency is required to plan ICIs therapy. In this study, the results of MSI test actually conducted in clinical practice were investigated. In total, 26,469 samples of various cancers were examined to determine if PD-1 blockade was indicated between December 2018 to November 2019. The results of MSI test were obtained for 26,237 (99.1%) among them. The male to female ratio was 51:49 and mean age was 64.3 years. In all the samples, overall frequency of MSI-H was 3.72%. By gender, the frequency of MSI-H was higher in female patients (4.75%) than in male patients (2.62%) (P < 0.001). A comparison by age revealed that the frequency of MSI-H was significantly higher in patients aged less than 40 years (6.12%) and 80 years or older (5.77%) than in patients aged between 60 and 79 years (3.09%) (P < 0.001). MSI-H was detected in 30 cancer types. Common cancer types were endometrial cancer, 16.85%; small intestinal cancer, 8.63%; gastric cancer, 6.74%; duodenal cancer, 5.60%; and colorectal cancer, 3.78%. MSI-H was detected in cancer derived from a wide variety of organs. The frequency of MSI-H varied by cancer types and onset age. These data should prove especially useful when considering ICI treatment. Supporting Information.