Breast Cancer Res Treat (2012) 136:267–275 DOI 10.1007/s10549-012-2257-4 E P I D E M I O L O G Y Exposure to polychlorinated biphenyl (PCB) congeners measured shortly after giving birth and subsequent risk of maternal breast cancer before age 50 Barbara A. Cohn • Mary Beth Terry • Marj Plumb • Piera M. Cirillo Received: 24 July 2012 / Accepted: 12 September 2012 / Published online: 28 September 2012 The Author(s) 2012. This article is published with open access at Springerlink.com Abstract Discrete windows of susceptibility to toxicants have been identiﬁed for the breast, including in utero, puberty, pregnancy, and postpartum. We tested the hypothesis that polychlorinated biphenyls (PCBs) mea- sured during the early postpartum predict increased risk of maternal breast cancer diagnosed before age 50. We ana- lyzed archived early postpartum serum samples collected from 1959 to 1967, an average of 17 years before diagnosis (mean diagnosis age 43 years) for 16 PCB congeners in a nested case–control study in the Child Health and Devel- opment Studies cohort (N = 112 cases matched to controls on birth year). We used conditional logistic regression to adjust for lipids, race, year, lactation, and body mass. We observed strong breast cancer associations with three congeners. PCB 167 was associated with a lower risk (odds ratio (OR), 75th vs. 25th percentile = 0.2, 95 % conﬁ- dence interval (95 % CI) 0.1, 0.8) as was PCB 187 (OR, 75th vs. 25th percentile = 0.4, 95 % CI 0.1, 1.1). In con- trast, PCB 203 was associated with a sixfold increased risk (OR, 75th vs. 25th percentile = 6.3, 95 % CI 1.9, 21.7). B. A. Cohn (&) P. M. Cirillo Child Health and Development Studies, Public Health Institute, 1683 Shattuck Avenue, Ste. B, Berkeley, CA 94709, USA e-mail: bcohn@chdstudies.org M. B. Terry Department of Epidemiology, Mailman School of Public Health of Columbia University, New York, NY, USA M. B. Terry Herbert Irving Comprehensive Cancer Center, Columbia University Medical Center, New York, NY, USA M. Plumb Plumbline Coaching and Consulting, Inc., 2759 Park Street, Berkeley, CA 94702, USA The net association of PCB exposure, estimated by a post- hoc score, was nearly a threefold increase in risk (OR, 75th vs. 25th percentile = 2.8, 95 % CI 1.1, 7.1) among women with a higher proportion of PCB 203 in relation to the sum of PCBs 167 and 187. Postpartum PCB exposure likely also represents pregnancy exposure, and may predict increased risk for early breast cancer depending on the mixture that represents internal dose. It remains unclear whether individual differences in exposure, response to exposure, or both explain risk patterns observed. Keywords PCBs Polychlorinated biphenyls cancer Pregnancy Postpartum Prospective Breast Human Abbreviations OR Odds ratio PCB(s) Polychlorinated biphenyl(s) 95 % CI 95 percent conﬁdence interval Introduction Discrete windows of susceptibility to toxicants have been identiﬁed for the breast, including in utero, during puberty, and during pregnancy and postpartum [1–4]. Human studies of breast cancer have not been able to assess the effects of measured exposure to environmental chemicals during windows of susceptibility for the breast [2, 5]. The existing literature on polychlorinated biphenyls (PCBs) and breast cancer typically has focused primarily on postmen- opausal breast cancer [6–8]. In addition, exposure in prior studies was largely measured in middle age or at time of diagnosis, was variable on how PCBs were classiﬁed and 123