Cancer not more deadly in dense breasts

Women with dense breasts are at increased risk of developing breast cancer but not of dying from the disease. So say results from a prospective study of more than 9,000 women with breast cancer by the Breast Cancer Surveillance Consortium.

Participants in the study, published in the Journal of the National Cancer Institute, were diagnosed with primary invasive breast carcinoma between 1996 and 2005. During almost 7 years of follow up, 1,795 women died, about half of whom (889) died of breast cancer.

The only women in whom the investigators found an increased risk of death from breast cancer were those with the least dense breasts (Breast Imaging Reporting and data System [BI-RADS] 1) who were obese or had tumors ≥ 2.0 cm. Risk was doubled in the former group and increased 55% in the latter group, whereas after adjustment for several variables (e.g. site; age and year of diagnosis; cancer stage; body mass index; mode of detection; treatment; income) dense breast tissue (BI-RADs 4) was not linked to either death from breast cancer or from any cause.

The study authors hypothesize that the increased risk in the low-density subgroups may be a result of higher percentages of fat in the breasts contributing to a “tumor microenvironment that facilitates cancer growth and progression.” Given the worldwide obesity epidemic, according to the researchers, increased surveillance may be needed in women with fatty breasts.

A limitation of the study is that the BI-RADS classification system is only moderately reliable, so in some women, breast density may have been misclassified. Detailed information on treatment, comorbidities, and weight changes during the course of the study also was lacking.

The investigators concluded that risk factors for breast cancer and those for increased mortality from the disease may differ.

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