Reduced Hb levels at diagnosis, preoperative and postoperative were found to be significantly associated with colon tumours (all p < 0.001), while a reduction in the Hb level due to surgery was more pronounced in patients with rectum tumours as compared to those with colon tumours (1.09 versus 0.96 mmol/L, p = 0.05). This evidence concerns the gene GSTM1 and colonic neoplasm.