The protective effect of full-term pregnancy against
breast cancer is thought to be induced by two
placental hormones:
human chorionic gonadotropin and human chorionic
somatotropin hormone (CSH) produced by the placental trophoblastic cells. We hypothesized that variants in placental genes encoding these
hormones may alter maternal
breast cancer risk subsequent to pregnancy. We conducted a case-control study to examine the association between polymorphisms in a woman's placental (i.e., her offspring's) homologous chorionic gonadotrophin beta5 (CGB5) and CSH1 genes and her post-pregnancy
breast cancer risk. A total of 293
breast cancer cases and 240 controls with at least one offspring with available
DNA were selected from the New York site of the
Breast Cancer Family Registry. Three single nucleotide polymorphisms (SNP) in CGB5 and CSH1 genes were genotyped for 844 offspring of the cases and controls. Overall, maternal
breast cancer risk did not significantly differ by the offspring's carrier status of the three SNPs. Among women with an earlier age at childbirth (younger than the median age of 26 years), those with a child carrying the variant C allele of CGB5 rs726002 SNP had an elevated
breast cancer risk [odds ratio (OR), 2.09; 95% confidence interval (95% CI), 1.17-3.73]. Among women with a later age at childbirth,
breast cancer risk did not differ by offspring's carrier status of CGB5 rs726002 SNP (OR, 0.90; 95% CI, 0.53-1.51; P for interaction=0.04). The findings suggest that placental CGB5 genotype may be predictive of maternal post-pregnancy
breast cancer risk among women who give birth early in life.