Higher oestriol levels in pregnancy may protect against breast cancer
Relatively high third-trimester level of oestriol (E3) appears to protect parous women against breast cancer, whereas oestrone (E1) and oestradiol (E2) may increase the risk, suggests a recent study.
To determine whether higher E3 in pregnancy was protective while higher E1 plus E2 increased breast cancer risk, researchers conducted a prospective case-cohort study (n=620; 204 cases) with a 38-year follow-up of 15,528 pregnant women in the Child Health and Development Studies. They measured E1, E2 and E3 in archived third-trimester serum and examined associations with breast cancer.
Participants included were Northern California Kaiser members who received obstetric care from 1959 to 1967. The main outcome measure was diagnosis of breast cancer through 1997.
An association existed between doubling of E1 plus E2 and greater risk of breast cancer (hazard ratio [HR], 1.7; 95 percent CI, 1.2 to 2.4). On the other hand, doubling of E3 or E3/E1 plus E2 correlated with protection (HR, 0.7; 0.5 to 1.0; HR, 0.6; 0.4 to 0.8, respectively).
These associations were stronger for diagnoses within 15 years after delivery compared with 16 to 38 years (p=0.0002 for interaction) for gravidas >27 years at delivery vs ≤27 years (p=0.01 for interaction) and for primiparas vs multiparas (p=0.02 for interaction).
“If findings are confirmed, third-trimester pregnancy oestrogens could help explain how parity affects breast cancer,” researchers said.
Full-term pregnancy is linked to a temporary increase and lifetime decrease in maternal breast cancer risk. E1, E2 and E3 are in high concentration during the third trimester. E1 and E2 metabolism produces carcinogenic intermediaries, while E3 metabolism does not, according to researchers.