Positive associations were found between serum GGT and development of ER+, ER− and PR+ breast cancers compared to controls (odds ratio (OR) 1.14 (95% confidence interval (CI) 1.08–1.19), 1.11 (1.01–1.23) and 1.18 (1.12–1.24), respectively) and of ER+/PR+ tumours. This evidence concerns the gene PGR and breast cancer.