We found inverse associations between GGT levels and PR− breast cancers compared to PR+ (OR 0.87 (0.80–0.95)), between ER+/PR− tumours compared to ER+/PR+ tumours and between ER−/PR−/HER+ compared to ER+/HER2 or PR+/HER2 tumours (OR 0.55 (95% CI 0.34–0.90). This evidence concerns the gene ERBB2 and breast carcinoma.