In women with primary breast cancer, high mammographic breast density is a risk factor for developing breast cancer in the contralateral breast.1

Women with dense mammographic breast density experience twice as high a risk of developing primary breast cancer. Researchers hypothesized that dense mammographic breast tissue would correlate with a higher risk of developing contralateral breast cancer.

This study, published in Cancer, examined female patients treated at The University of Texas MD Anderson Cancer Center in Houston, Texas. These patients were treated for sporadic, American Joint Committee on Cancer (AJCC) stage I to stage III breast cancer between January 1997 and December 2012. The AJCC defines and popularizes cancer staging systems.

Researchers identified patients (n = 229) who had developed metachronous contralateral breast cancer and selected 1:2 matched controls. Controls (n = 451) did not develop contralateral breast cancer using incidence density sampling. They were matched on year of diagnosis, attained age, and hormone receptor status of the first breast cancer.

American College of Radiology breast categories of fatty or scattered density, heterogeneous density, and extreme density determined mammographic breast density at the time of first breast cancer diagnosis.

Among patients who developed contralateral breast cancer, 39.3% had nondense breast tissue, and 60.7% had dense breast tissue. Among the controls, 48.3% had nondense breast tissue and 51.7% had dense breast tissue.

The odds of developing contralateral breast cancer were significantly higher for patients with dense breasts than for patients with nondense breasts after adjustment for potential prognostic risk factors for breast cancer  (odds ratio, 1.80; 95% CI, 1.22-2.64 [P <.01]). Researchers used multivariable conditional logistic regression models for statistical analysis.

In addition, patients who received endocrine therapy or chemotherapy were less likely to develop contralateral breast cancer.

Reference

1. Raghavendra A, Sinha AK, Le-Petross HT, et al. Mammographic breast density is associated with the development of contralateral breast cancer. Cancer. 2017 Jan 30. doi: 10.1002/cncr.30573 [Epub ahead of print]