In the group with three night shifts, a reduced risk of breast cancer was associated with the presence of one variant allele (heterozygote) or two variant alleles (homozygote) for SNPs in CLOCK rs11133373 (OR 0.50, 95% CI 0.25- 0.99), CLOCK rs3749474 (OR 0.56, 95% CI 0.31- 0.99); ROR-b rs3903529 (OR 0.57, 95% CI 0.34- 0.95), ROR-b rs7022435 (OR 0.16, 95% CI 0.05- 0.55); ROR-b rs7022435 (OR 0.17, 95% CI 0.03- 0.84); ROR-b rs3750420 (OR 0.40, 95% CI 0.18- 0.88) and MTNR1A rs 13113549 (OR 0.50, 95% CI 0.28- 0.90). The gene discussed is MTNR1A; the disease is breast carcinoma.