br To evaluate whether risks differed within certain subsets
To evaluate whether risks differed within certain subsets of our study population, a number of stratified analyses were conducted. Subsets of interest were chosen a priori based on our review of the literature. Selected subsets included: pre/peri-menopausal versus post-menopausal women; cases with hormonally responsive tumors, identi-fied as Jasplakinolide or progesterone receptor positive (ER+/PR+) versus non-hormonally responsive tumors that were estrogen-receptor nega-tive and progesterone-receptor negative (ER-/PR-); women who had and had not ever used menopausal HT; women with low, medium and high BMI; women who had and had not ever breastfed; women who reported changes in body weight versus those with stable body weight (≤5 pound change in body weight between enrollment in the study in 1995–1996 and the 2011–2012 mailed survey). Additionally, to explore whether risks were confined to women who may have been exposed to PBDEs during critical windows of susceptibility, we examined risks among women who entered menopause or experienced their first full-term pregnancy between 1990 and 2000 – the interval of time when U.S. population PBDE exposures were likely at their peak (Guo et al., 2016; Petreas et al., 2003; She et al., 2002; Sjodin et al., 2004). Due to small numbers in some subsets, regression models for these analyses were adjusted only for the matching design variables and total serum lipids.
Two additional analyses were conducted to indirectly evaluate po-tential biases that could have been introduced by the post-diagnostic assessment of serum PBDE concentrations. These included: 1) evalu-ating the Spearman Rank correlations between PBDE serum con-centrations and the time interval between diagnosis and blood draw; and 2) repeating our logistic regression analyses, stratified by the time interval between diagnosis and blood draw (≤3 years and > 3 years).
Participants were predominantly middle-aged and older non-Hispanic white women, reflecting the characteristics of the CTS cohort from which microfilaments were selected. The median age of study participants at CTS baseline enrollment was 49 years (range = 24–71) and was 66 years (range = 41 to 87) at the time of blood collection for this
Distribution of selected characteristics for 1838 study participants.a,b
N Percent N Percent N Percent
Age at baseline
City of Hope
Family history of breast
cancer (first degree
Long-term strenuous &
Parity/age at first full-
(HT) use at blood
Pre- or peri-menopausal
Table 1 (continued)
N Percent N Percent
a Includes all characteristics that were included as covariates in the fully-adjusted multivariable logistic regression models.
b Characteristic assessed at CTS baseline enrollment, unless otherwise noted. c Distributions for cases and controls were statistically different (i.e., p (chisq) < 0.05). d Long-term physical activity includes activity from high-school through current age or age 54 if 55 years of age or older.
study. Compared to controls, cases were significantly more likely to be older and post-menopausal. Cases also were significantly more likely than controls to report a family history of breast cancer, have higher BMI, report less physical activity, and consume more pork. Controls were significantly more likely than cases to have had their blood sample collected during the initial few months of the study and during the fall and winter months (Table 1). All factors as specified in Table 1 were included as covariates in our logistic regression analyses.