Women treated for breast cancer have a small but significantly higher risk of developing lung cancer, according to a large study presented at the European Society for Radiotherapy and Oncology (ESTRO33) meeting in Vienna.
The research shows that cancer risk increases based on the amount of radiation absorbed by the tissue.
"Our findings suggest that any reduction in the dose of radiation to the lung would result in a reduction in the risk of radiation-induced subsequent lung cancers, Dr. Trine Grantzau said in a statement. "With the advances in breast cancer treatment and the introduction of breast cancer screening, a growing number of women are becoming long-term survivors, and so we need to have an increased awareness of treatment-induced second cancers and take steps to reduce those risks by using radiotherapy techniques that spare normal tissue as much as possible."
Grantzau and colleagues from Aarhus University Hospital in Aarhus, Denmark, examined the incidence of primary lung cancers among 23,627 women who had been treated with postoperative radiotherapy for early breast cancer between 1982 and 2007.
In all, 151 (0.6%) were diagnosed with a new primary lung cancer, and they were matched with a control group of 143 women who did not develop the disease, the researchers reported. The study aimed to determine if there was a dose-response correlation for second primary lung cancer after breast cancer irradiation, and to estimate the excess relative risk per delivered Gy to the lung tissue.
Armed with radiotherapy records, x-rays, and treatment information, the researchers estimated the radiation dose of the original breast cancer delivered to the lung region where the tumor was later found, testing their results on a phantom to account for higher doses delivered to areas outside the main field of radiation.
The median age when a second primary lung cancer was diagnosed was 68 (range 46-90), compared with a median age of the breast cancer diagnosis of 54 years. Fully 91% of the lung cancer cases were in smokers compared with 40% of the controls, the group reported.
The mean average dose of radiotherapy during breast cancer treatment to the tumor region was 8.7 Gy, versus 5.6 Gy among women who did not develop breast cancer.
The results show that the risk of second lung cancer after radiotherapy in early breast cancer patients is associated with the radiation dose delivered dose to the lung, Grantzau said in the statement.
