Adjuvant radiotherapy for breast cancer as a risk factor for the development of lung cancer.

Women diagnosed with primary breast or lung cancer and recorded between 1972 and 1989 in our tumor registry were identified. Of 4,123 lung cancer patients and 3,537 breast cancer patients, 42 patients with both diagnoses were identified. The two malignancies were diagnosed simultaneously in five patients, lung cancer was diagnosed first in six patients and breast cancer was diagnosed first in 31 (p < 0.001). Nineteen of those 31 patients received adjuvant radiotherapy for breast cancer and developed lung cancer a median of 17 years later. Of the 19 irradiated patients who subsequently developed lung cancer, 15 did so in the ipsilateral lung and only four had lung cancer contralateral to the previously irradiated site (p < 0.001). Adjuvant radiotherapy for breast cancer as delivered decades ago may be an etiologic factor for lung cancer.