Type 2 diabetes mellitus and malignant tumors are two kinds of chronic diseases with tremendous impact on human health. Numerous epidemiological and clinical studies have shown that type 2 diabetes mellitus increases the risk of liver, pancreatic, endometrial, gallbladder, colorectal and breast cancers. Hyperglycemia can promote cancer cell proliferation, migration, invasion and immune escape through a variety of direct and indirect mechanisms. Insulin resistance and hyperinsulinemia can activate multiple signal transduction pathways through insulin/IGF-I signaling axis and promote tumorigenesis. Sustained chronic inflammatory responses can promote the development of cancer through DNA damage and pro-inflammatory factors. Gut microbiome dysbiosis is closely related to the occurrence of several gastrointestinal tumors. This paper reviews the progress on the correlation between type 2 diabetes mellitus and the progression of malignant tumors and the possible mechanisms.

Squalene monooxygenase (SQLE) is the rate-limiting enzyme of cholesterol biosynthesis. It plays a crucial role in regulating cholesterol homeostasis. Increasing evidence shows that SQLE is closely related to the occurrence, development, metastasis, and poor prognosis of various cancers. SQLE can not only promote the proliferation of cancer cells and epithelial-mesenchymal transformation but also play an important role in maintaining the stemness of cancer stem cells and regulating cholesterol homeostasis. SQLE may be a potential molecular target for cancer therapy. In this review, the role of SQLE in regulating cholesterol homeostasis in vivo; its function in the occurrence, development, and metastasis of various cancers; and its molecular mechanism were summarized. Screening new SQLE inhibitors may provide new ideas for targeted cancer therapy.