Mean arterial pressure, pregnancy-induced hypertension, and preeclampsia: evaluation as independent risk factors and as surrogates for high maternal serum alpha-fetoprotein in estimating breast cancer risk.

Data from a nested case-control study were analyzed to examine high mean arterial pressure (MAP), hypertension of pregnancy, and preeclampsia as independent predictors and as surrogate markers for elevated alpha-fetoprotein (AFP) levels in evaluating breast cancer risk. Cases (n = 205) were identified by the California Cancer Registry from a cohort of pregnant women who were part of the Kaiser Health Plan and took part in the Child Health and Development Studies initiated by the University of California, Berkeley, from June 1959 to September 1966. Controls (n = 337) were selected by randomized recruitment from the same cohort probability matched to cases by distribution of birth dates of cases. High MAP was associated with breast cancer risk and is different across quartile of age at first full-term pregnancy as is high AFP. Odds ratios (OR) across quartiles for MAP were 0.24 [95% confidence interval (CI), 0.08-0.71], 0.84 (95% CI, 0.39-1.66), 1.00 (referent), and 2.50 (95% CI, 1.21-5.13), and for AFP were 0.34 (95% CI, 0.13-0.93), 0.77 (95% CI, 0.36-1.67), 1.00 (referent), and 2.38 (95% CI, 1.13-5.00). Neither diagnosed preeclampsia nor hypertension of pregnancy showed any association with breast cancer risk. When both high AFP and high MAP were entered into the same analysis, neither changed the OR for the other more than 8%. Additionally, AFP level was not a linear function of MAP. Although the pattern of ORs across quartiles of age at first full-term pregnancy was similar for the two variables, it cannot be concluded that high MAP is an adequate surrogate for high levels of maternal serum AFP, but rather represents some related process that is in and of itself a risk factor for breast cancer.