Human chorionic gonadotropin (hCG) is necessary for the maintenance of early pregnancy and promotes normal breast cell differentiation. Administered hCG reduces risk of carcinogen-induced breast cancer in animal models, and higher circulating hCG concentrations were associated with significantly lower long-term risk of breast cancer in a prior nested case-control study. In this study, we investigated early pregnancy hCG concentrations and subsequent breast cancer risk.
We conducted a nested case-control study with 1,191 cases and 2,257 controls (matched on age and date at blood collection) in the Finnish Maternity Cohort (FMC), a cohort with serum samples from 98% of pregnancies registered in Finland since 1983. This study included women with a serum sample collected early (<140 days gestation) in their first pregnancy resulting in a live, term birth. Breast cancer cases were identified via the Finnish Cancer Registry. Age at breast cancer diagnosis ranged from 22–58 years (mean: 41 years). hCG was measured using a solidphase competitive chemiluminescence assay. Odds ratios (ORs) were calculated using conditional logistic regression.
We observed no association between hCG and breast cancer risk, overall (Quartile 4 vs. 1, OR: 1.14 95% confidence interval [0.94–1.39]), by estrogen and progesterone receptor status, or by ages at first term birth or diagnosis. Associations did not differ by time between pregnancy and diagnosis (e.g., <5 years, ORQ4 vs. Q1: 1.10 [0.64–1.89]; ≥ 15 years, ORQ4 vs. Q1: 1.36 [0.86–2.13]; p heterogeneity=0.62).
This large prospective study does not support an inverse relationship between early pregnancy serum hCG concentrations and breast cancer risk.