GSTO1 and breast cancer: Regarding other GST classes, increased expression of GSTA1 is confirmed in colorectal cancer [39], GSTO1-1 is upregulated in transitional cell carcinoma [40], esophageal squamous cell carcinoma [41], pancreatic cancer [42], and breast cancer [43], while GSTM1 overexpression is observed in transitional cell carcinoma of urinary bladder [31], renal cell carcinoma [33] and breast cancer [44].