In addition, it has recently been reported that Megasphaera is present in the tumors of patients with pancreatic ductal adenocarcinoma (PDAC) who have survived for a long time (40), and that short-chain fatty acids such as butyrate and pentanoate, which are induced by Megasphaera, regulate the response of CD8-positive T cells and enhance the effects of cancer immunotherapy (41). This evidence concerns the gene CD8A and cancer.