Based on this, we screened published studies related to VDR expression and prognosis of malignant tumours and included eight related studies on digestive system tumours (three on colorectal cancer, three on oesophageal cancer, one on pancreatic cancer, and one on cholangiocarcinoma) [6, 7, 9, 10, 12–16]. This evidence concerns the gene VDR and colorectal cancer.