Inflammatory vs Noninflammatory Breast Cancers of Same Estrogen Receptor Status Have Varying Risk Factor Associations
In a study reported in the Journal of the National Cancer Institute, Catherine Schairer, PhD, from the National Cancer Institute, and colleagues investigated risk factors associated with inflammatory breast cancer. Among their findings was that high body mass index (BMI) increased inflammatory breast cancer risk irrespective of menopausal status and estrogen receptor status.
Study Details
The study included 617 inflammatory breast cancer cases in a nested case-control study from the Breast Cancer Surveillance Consortium database (1994–2009), 1,151 noninflammatory locally advanced invasive breast cancers with chest wall/breast skin involvement, 7,600 noninflammatory invasive cases without chest wall/breast skin involvement, and 93,654 control subjects matched to case subjects for age and year at diagnosis and mammography registry. Estimated rate ratios were derived from conditional logistic regression analyses for each case group vs control subjects based on multiply imputed datasets.
Associations With BMI
First-degree family history of breast cancer and high mammographic breast density increased risk of inflammatory breast cancer and noninflammatory invasive disease in a similar manner. However, contrary to findings for noninflammatory invasive breast cancer, high BMI (≥ 30 kg/m2) was associated with substantially increased risk of inflammatory breast cancer in both premenopausal women (RR = 3.90, 95% confidence interval [CI] = 1.50–10.14) and in peri/postmenopausal women not currently using hormones (RR = 3.70, 95% CI = 1.98–6.94) and currently using hormones (RR = 2.94, 95% CI = 1.10–7.90) compared with BMI < 25 kg/m2, as was risk for both estrogen receptor–positive (RR = 4.21, 95% CI = 1.91–9.28) and estrogen receptor–negative inflammatory breast cancer (RR = 3.35, 95% CI = 1.73–6.49). High BMI was also associated with slightly increased risk of estrogen receptor–positive breast cancer (RR = 1.40, 95% CI = 1.11–1.76).
Associations With Age at First Birth and Education Level
Later age at first birth was associated with reduced risk of estrogen receptor–negative inflammatory breast cancer (RR = 0.24, 95% CI = 0.07–0.87, for > 30 years vs < 20 years), with the reduction being greater than the nonsignificant risk reductions for estrogen receptor–negative noninflammatory invasive breast cancer.
Higher level of education was associated with reduced risk of estrogen receptor–positive inflammatory disease, with risk reductions being greater than those for estrogen receptor–positive noninflammatory invasive disease. Risk of estrogen receptor–positive inflammatory breast cancer was significantly reduced with education level of college/postgraduate (RR = 0.31, 95% CI = 0.18–0.52), some college (RR = 0.38, 95% CI = 0.24–0.61), and high school/GED (RR = 0.43, 95% CI = 0.21–0.89) vs less than high school. None of the associations was significant for noninflammatory invasive disease except for reduced risk of estrogen receptor–positive noninflammatory locally advanced invasive breast cancers with chest wall/breast skin involvement with college/postgraduate education vs less than high school diploma (RR = 0.60, 95% CI = 0.38–0.95).
The investigators concluded: “Varying risk factor associations between inflammatory and noninflammatory breast cancer suggest a distinct etiology for this clinically unique type of breast cancer. Future research on [inflammatory breast cancer] should attempt to account for the differential distribution patterns of molecular subtypes between [inflammatory and noninflammatory disase] in an effort to identify risk factors that are [inflammatory breast cancer] specific rather than subtype specific.”
The study was supported by the National Cancer Institute.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
