Variations in Risk Factors Suggest Distinct Etiology for Inflammatory Breast Cancer

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“Varying risk factor associations between inflammatory and noninflammatory breast cancer suggest a distinct etiology for [inflammatory] breast cancer,” according to a study in the Journal of the National Cancer Institute. High body mass index was shown to increase risk of inflammatory breast cancer “irrespective of menopausal status and estrogen receptor (ER) expression,” the researchers reported. 

The study included 617 inflammatory breast cancer case subjects in a nested case–control study from the Breast Cancer Surveillance Consortium database (1994–2009), reported Catherine Schairer, PhD, of the National Cancer Institute, and colleagues. “We also included 1,151 noninflammatory, locally advanced, invasive breast cancers with chest wall/breast skin involvement, 7,600 noninflammatory invasive case subjects without chest wall/breast skin involvement, and 93,654 control subjects matched to case subjects on age and year at diagnosis, and mammography registry.” 

“The average age of diagnosis for [inflammatory breast cancer] case subjects was 4 years younger than for [noninflammatory disease] case subjects,” the authors noted. Risk factor associations with family history of breast cancer and mammographic breast density were similar for all groups. 

Besides high body mass index, other risk factor variations were later age at first birth (which was associated with a reduced risk of ER-negative inflammatory breast cancer greater than for ER-negative noninflammatory disease) and education level. A higher level of education was “associated with reduced risk of ER-positive [inflammatory breast cancer], more so than for noninflammatory breast cancer,” the investigators reported. 

“Notably, overweight and obesity statuses were associated with increased [inflammatory breast cancer] risk regardless of the internal hormonal milieu or the ER status of the tumors,” the researchers commented. They found that among patients with inflammatory breast cancer, the “rate ratios for [body mass index of] 30 and greater vs [body mass index] less than 25 were 3.90 (95% CI = 1.50–10.14) in premenopausal women and 3.70 (95% CI = 1.98–6.94) in peri/postmenopausal women not currently using hormones.” 

Accompanying Commentary

According to an editorial accompanying the article, “These findings show conclusively that obesity is a strong risk factor for [inflammatory breast cancer], and they are in stark contrast with the far lower rate ratios for the association of obesity with other breast cancer types, which ranged from 1.02 to 1.36. This finding supports the idea that [inflammatory breast cancer] is a distinct epidemiologic entity, in addition to being a distinct clinicopathologic entity,” wrote the editorialists.

“Understanding the mechanism by which obesity contributes to the risk of breast cancer is important and may lead to identification of some biologic targets. However, the greatest need is to modify behavior and stop the obesity epidemic in the first place,” they concluded. ■

Schairer C, et al: J Natl Cancer Inst 105:1373-1384, 2013.
Amiri-Kordestani L, et al: J Natl Cancer Inst 105:1340-1342, 2013.