(HealthDay News) — For patients with breast cancer, the absolute risks associated with modern radiotherapy are higher for smokers than nonsmokers, according to research published online March 20 in the Journal of Clinical Oncology.
Carolyn Taylor, D.Phil., from the University of Oxford in the United Kingdom, and colleagues estimated the absolute long-term risks of modern breast cancer radiotherapy. They conducted a systematic literature review of lung and heart doses in breast cancer regimens published from 2010 to 2015. Individual patient data for 40,781 women randomized to breast cancer radiotherapy versus no radiotherapy were meta-analyzed to yield rate ratios (RRs) for second primary cancers and cause-specific mortality and excess rate ratios (ERRs) for incident lung cancer and cardiac mortality per Gy.
The researchers found that the average radiation doses were 5.7 and 4.4 Gy for whole lung and whole heart, respectively. Lung cancer incidence ≥10 years after radiotherapy had a RR of 2.10 on the basis of 134 cancers (0.11 ERR per Gy whole-lung dose). On the basis of 1,253 cardiac deaths, the RR was 1.30 for cardiac mortality (0.04 ERR per Gy whole-heart dose). The estimated absolute risks from modern radiotherapy were about 4 and 0.3 percent for long-term continuing smokers and nonsmokers, respectively, for lung cancer, and 1 and 0.3 percent for smokers and nonsmokers, respectively, for cardiac mortality.
“Smoking can determine the net effect of radiotherapy on mortality, but smoking cessation substantially reduces radiotherapy risk,” the authors write.
Several authors disclosed financial ties to the pharmaceutical industry.