G6PD and breast cancer: G6PD deficiency causes hereditary hemolytic anemia.13 Expression of G6PD is upregulated in numerous cancers, including esophageal squamous cell carcinoma,14 breast cancer,15 hepatocellular carcinoma,16 17 colon and colorectal cancer,18 19 renal cell carcinoma,20 bladder cancer21 and cervical cancer,22 and is associated with tumor cell proliferation, migration and invasion.14–22 To our knowledge, no studies have reported on the role of G6PD in MCC.