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A new study by Swedish researchers finds that women who have undergone radiation therapy for breast cancer may be at higher risk of developing lung cancer later in life, especially if they also smoke. The study suggests that an interaction between radiation therapy and smoking may be responsible for the lung cancer cases. The risk of lung cancer was highest among women who were diagnosed with breast cancer before age 50. The study underscores that need to investigate the long-term effects of cancer therapies, especially since many breast cancer patients are being diagnosed with the disease in early stages and increasing their odds of survival. To conduct their study, Dr. Michaela Prochazka and colleagues from the Karolinska Institute in Stockholm, Sweden used the Swedish Cancer Registry to identify approximately 141,000 women who had been diagnosed with breast cancer between 1958 and 1997. Among these women, 613 later developed lung cancer. According to the research, after five years of their breast cancer diagnoses, women with breast cancer were more likely to develop lung cancer than women who had not been previously diagnosed with breast cancer. However, during the first one to four years of their breast cancer diagnoses, these women were less likely to develop lung cancer. The researchers then studied 174 women for whom they had information about which breast was treated with radiation therapy. After ten years of their breast cancer diagnoses, these women faced a higher than average risk of developing lung cancer on the same side of their body as they received prior radiation therapy for breast cancer. The risk of lung cancer from radiation was higher among the women born between 1930 and 1949, when a larger percentage of the U.S. population smoked. Thus, Dr. Prochazka and his colleagues conclude that, "women with breast cancer have a significantly increased risk of developing a subsequent lung cancer possibly related to an interaction between radiotherapy and smoking." This heightened risk of lung cancer continued up to 20 years after the initial breast cancer diagnosis. Other studies have also investigated the link between breast cancer and a later lung cancer diagnosis. In a study published in the June 2000 issue of the Journal of Clinical Oncology, Edward Obedian and fellow Yale researchers found that women treated with lumpectomy and radiation who continued to smoke were at higher risk of developing lung cancer than similar patients who did not smoke. This also suggests an interaction between radiation therapy and smoking. They did not find a higher risk of lung cancer among women treated with lumpectomy and radiation compared to those treated with mastectomy and no radiation. Other research has linked smoking with a higher risk of the spread (metastasis) of breast cancer to the lungs. In a study of 261 women with breast cancer, researchers from the University of California- Davis Medical Center found that the women who smoked were more likely to experience lung metastases than women who did not smoke. However, the researchers warned that there may be other factors that explain why the smokers in their study were more likely to have their breast cancer spread to the lungs than the non-smokers. According to Dr. Murin, smokers tend to exercise less and maintain less healthy diets than non-smokers, which may influence their cancer outcome. Therefore, more research is needed to help determine the exact relationship between breast cancer and smoking. Lung cancer is the number one cause of cancer-related deaths in the United States. The American Cancer Society estimates that in 2002 there will be 169,400 new cases of lung cancer: 90,200 among men and 79,200 among women. Breast cancer is the most common cancer among women excluding skin cancers: in 2002, 203,500 new cases of invasive breast cancer (Stages I-IV) will be diagnosed.
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