(HealthDay News) — Younger women who smoke appear to be at increased risk for developing estrogen receptor (ER)-positive breast cancer, according to research published online Feb. 10 in Cancer.

Masaaki Kawai, M.D., Ph.D., of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues conducted a case-control study of women, aged 20 to 44 years, who were diagnosed with invasive breast cancer (ER-positive, 778; ER-negative, progesterone receptor-negative, and human epidermal growth factor-negative [triple-negative], 182) and 938 women without cancer (controls). The researchers sought to assess the association between smoking and risk of breast cancer.

The researchers found that female ever-smokers were 1.3 times more likely to develop breast cancer (95 percent confidence interval [CI], 1.1 to 1.7), including increased risk of ER-positive breast cancer (odds ratio [OR], 1.4; 95 percent CI, 1.1 to 1.8), but not triple-negative breast cancer (OR, 1.1; 95 percent CI, 0.7 to 1.6). Women who were current or recent smokers with a 10 pack-year or greater history of smoking were at increased risk for ER-positive breast cancer (OR, 1.6; 95 percent CI, 1.1 to 2.4), but not triple-negative breast cancer (OR, 1.0; 95 percent CI, 0.5 to 1.9).

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“The results from this study suggest that smoking history, and particularly longer term, recent smoking, is associated with a modest increase in the risk of ER-positive breast cancer, but not with the risk of triple-negative breast cancer,” the authors write.

One of the study authors received a grant from the Banyu Life Science Foundation International.

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