A systematic review of 26 primary care studies reported that the sensitivity of FIT for CRC in symptomatic patients at the threshold of ≥10 μg Hb/g faeces is 87% (95% confidence interval [CI] = 81.0% to 91.6%) with a corresponding specificity of 84.4% (95% CI = 79.4% to 88.3%).7 Although these metrics outperform other tests GPs currently use to select patients for suspected cancer referral, such as chest X-ray and cancer antigen 125, it means 1 in 10 patients with CRC will have a negative FIT. Here, GSTM1 is linked to colorectal carcinoma.