GSTM1 and skin basal cell carcinoma: The GSH marker showed significant associations only with cancer subtype category (p = 0.001); the mean GSH value of the control group (5.47 μmol/g Hb) was found to be significantly greater than that of the BCC group (4.48 μmol/g Hb, p = 0.002) and that of the actinic keratosis (4.41 μmol/g Hb, p < 0.001).