Risk of primary lung cancer after treatment for breast cancer: two meta-analyses

Two meta-analyses, based on more than four million cases found that patients treated for breast cancer compared to the general population were more likely to develop primary lung cancer (SIR=1.25; p<0.001). This risk was affected by smoking (OR=9.73; p<0.001), radiotherapy (RR=1.40; p<0.001), chemotherapy (RR=0.69; p=0.002), positive ER status (RR=0.93; p=0.014), and positive PR status (RR=0.89; p<0.001). Subgroup analysis indicated that radiotherapy only increased the risk of ipsilateral lung cancer in breast cancer patients.