(ChemotherapyAdvisor) –  Survivors of estrogen-receptor-negative (ER-) breast cancer face an elevated risk of developing lung cancer, according to a study of cancer registry data published in Cancer Causes & Control

The study’s findings “suggest a higher overall risk of second lung cancer after ER- breast cancer compared with rates after ER+ breast cancer and those in the general population,” reported lead author Sara J. Schonfeld, MD, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland, and her coauthors.

“Radiotherapy, an established risk factor for second lung cancers among breast cancer survivors, does not appear to explain this observed risk,” Dr. Schonfeld and her coauthors were quick to note.

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Using the US National Cancer Institute’s Surveillance, Epidemiology and End Results (NCI-SEER) database, the authors analyzed second primary lung cancer risks for 222,148 1-year breast cancer survivors. Lung cancer rates were significantly higher after ER- breast cancers, but not after ER+ breast cancers (standardized incidence ratios [SIRs] = 1.20 vs. 0.96), the authors reported.

There might also exist a reciprocal risk, with lung cancer patients being at higher risk for ER- breast cancer, the authors reported. Subsequent analysis showed a trend toward higher risk of developing ER- breast cancer after lung cancer, as well (RR=1.29, 95% CI, 0.98-1.70).

“The parallel increase for a second lung cancer following an ER- first breast cancer and for a second ER- breast cancer after a first lung cancer suggests that there may be shared etiologic factors for these cancers,” the authors wrote.

Primary lung cancers represent approximately 5% of cancers among breast cancer survivors overall and are associated with poor survival. Because this is the first study of its kind, replication using data from another large registry is needed, the authors cautioned.