Table 4

Multivariate* relative risks (95% CI) for ER+/PR+ breast cancers by quartile of plasma prolactin concentration among postmenopausal women in the Nurses’ Health Study

n, case/controlProlactin ConcentrationsP for trend
≤7.4 ng/mL>7.4–9.4 ng/mL>9.4–12.3 ng/mL>12.3 ng/mL
By postmenopausal hormone use at blood draw
 Never user111/5451.0 (ref.)1.041.741.890.16
(0.54, 1.97)(0.95, 3.16)(1.02, 3.50)
 Past user67/2771.0 (ref.)1.001.762.330.02
(0.42, 2.40)(0.82, 3.78)(1.06, 5.14)
 Current user219/4531.0 (ref.)0.761.291.550.01
(0.44, 1.31)(0.79, 2.12)(0.98, 2.47)
By time between blood draw and diagnosis (for cases)§
 0–2 y52/1,2751.0 (ref.)2.014.233.100.04
(0.68, 5.98)(1.57, 11.4)(1.11, 8.62)
 2–4 y74/1,2751.0 (ref.)0.771.632.230.02
(0.33, 1.80)(0.80, 3.33)(1.13, 4.41)
 4–8 y161/1,2751.0 (ref.)0.671.201.560.02
(0.39, 1.16)(0.75, 1.94)(0.99, 2.47)
 8+ y110/1,2751.0 (ref.)1.051.331.580.03
(0.57, 1.94)(0.74, 2.38)(0.90, 2.79)
Adjusting for estrone or estradiol among never and past postmenopausal hormone users
 Not adjusted175/7841.0 (ref.)1.001.731.990.01
(0.59, 1.69)(1.06, 2.81)(1.20, 3.30)
 Estrone131/5971.0 (ref.)0.821.642.180.02
(0.44, 1.54)(0.92, 2.92)(1.21, 3.94)
 Estradiol175/7841.0 (ref.)0.981.771.930.01
(0.57, 1.66)(1.08, 2.90)(1.16, 3.22)
  • Abbreviations: ER, estrogen receptor; PR, progesterone receptor; BMI, body mass index.

  • * Adjusted for BMI at age 18, weight change from age 18 to blood draw, family history of breast cancer, age at menarche, age at first birth/parity, age at menopause, and matching factors.

  • Determined using continuous, log-transformed prolactin concentrations.

  • The P-interaction between past and never users was 0.41 and between current and never users was 0.77.

  • § The P-heterogeneity was 0.67, determined using polytomous logistic regression and the likelihood ratio test, comparing a model constraining relative risks to be the same across all case groups versus a model allowing the relative risks to differ across case groups.