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BAT-26 instability, a sensitive marker for the high-frequency microsatellite instability (MSI-H) phenotype, was analyzed in samples of gastric cancer and in adjacent intestinal metaplastic mucosae. Although all MSI-H gastric cancer samples showed BAT-26 instability, as assessed using 12 dinucleotide microsatellite markers, BAT-26 instability was not found in the adjacent intestinal metaplastic mucosa in any of the samples.

The small GTPases RalA and RalB are members of the Ras family and activated downstream of Ras. Ral proteins are found in GTP‐bound active and GDP‐bound inactive forms. The activation process is executed by guanine nucleotide exchange factors, while inactivation is mediated by GTPase‐activating proteins (GAPs). RalGAPs are complexes that consist of a catalytic α1 or α2 subunit together with a common β subunit. Several reports implicate the importance of Ral in pancreatic ductal adenocarcinoma (PDAC). However, there are few reports on the relationship between levels of RalGAP expression and malignancy in PDAC. We generated RalGAPβ‐deficient PDAC cells by CRISPR‐Cas9 genome editing to investigate how increased Ral activity affects malignant phenotypes of PDAC cells. RalGAPβ‐deficient PDAC cells exhibited several‐fold higher Ral activity relative to control cells. They had a high migratory and invasive capacity. The RalGAPβ‐deficient cells grew more rapidly than control cells when injected subcutaneously into nude mice. When injected into the spleen, the RalGAPβ‐deficient cells formed larger splenic tumors with more liver metastases, and unlike controls, they disseminated into the abdominal cavity. These results indicate that RalGAPβ deficiency in PDAC cells contributes to high activities of RalA and RalB, leading to enhanced cell migration and invasion in vitro, and tumor growth and metastasis in vivo.