Table 2.

Relationship between circulating prolactin levels and risk of total and ER+ breast cancer among all cases and controls (NHS and NHSII), by timing of blood draw in relation to breast cancer diagnosis/reference date and menopausal status at blood collection

Prolactin <10 years before diagnosis, proximate (ng/mL)Prolactin 10–20 years before diagnosis, distant (ng/mL)
≤8.1>8.1–11.0>11.0–15.7>15.7P-trenda≤8.1>8.1–11.0>11.0–15.7>15.7P-trenda
All cases
n, cases/controls545/946555/1004696/1039672/1032272/373226/344224/310231/312
RRb1.000.981.161.200.0051.000.920.960.970.94
95% CI(0.84–1.14)(1.00–1.35)(1.03–1.40)(0.72–1.17)(0.75–1.23)(0.75–1.25)
Premenopausalc
n, cases/controls148/287212/424281/586382/72063/7585/104104/134154/200
RRb1.001.000.941.050.541.001.061.011.030.98
95% CI(0.77–1.29)(0.73–1.21)(0.82–1.33)(0.67–1.67)(0.66–1.56)(0.68–1.56)
Postmenopausalc
n, cases/controls400/670340/569407/430298/335213/302137/236116/17381/115
RRb1.001.001.481.370.00021.000.860.960.930.97
95% CI(0.83–1.21)(1.23–1.80)(1.11–1.69)(0.65–1.14)(0.70–1.30)(0.66–1.33)
ER+ Cases
n, cases314335413400193152146144
RRb1.001.021.221.280.0031.000.900.920.890.49
95% CI(0.85–1.23)(1.02–1.46)(1.07–1.54)(0.69–1.18)(0.70–1.21)(0.66–1.18)
Premenopausalc
n, cases8510816220843636587
RRb1.000.820.870.980.471.001.050.880.810.21
95% CI(0.59–1.13)(0.64–1.18)(0.73–1.32)(0.64–1.75)(0.54–1.45)(0.51–1.30)
Postmenopausalc
n, cases229227251192150898157
RRb1.001.161.581.520.00021.000.810.980.970.81
95% CI(0.93–1.45)(1.26–1.98)(1.19–1.93)(0.59–1.12)(0.70–1.39)(0.65–1.43)
  • aPtrend determined using the median values of the quartiles as a continuous term.

  • bUnconditional logistic regression models to calculate RRs and 95% CIs, adjusting for age at blood draw (continuous), date of blood draw (continuous), fasting status and time of day of blood draw (fasting and morning draw, other), menopausal status/PMH use at blood draw (premenopausal/unknown, postmenopausal not using PMH, postmenopausal using PMH), BMI (continuous), age at menarche (continuous), history of BBD (yes, no), family history of breast cancer (yes, no), age at menopause (continuous), average childhood body size at ages 5 and 10 (continuous), and cohort (NHS, NHSII).

  • cPremenopausal (includes women of unknown menopausal status): 403 cases from the NHS and 620 from the NHSII for the proximate analysis and 306 cases from the NHS and 100 cases from the NHSII for the distant analysis. Postmenopausal: 1,392 cases from the NHS and 53 from the NHSII for the proximate analysis and 531 cases from the NHS and 16 cases from the NHSII for the distant analysis. For the proximate analysis, the Pinteraction by menopausal status was 0.01 for all cases and 0.02 for ER+ cases; the comparable Pinteractions by cohort were 0.17 and 0.05, respectively.