3D conformal radiotherapy is not associated with the long-term cardiac mortality in breast cancer patients: a retrospective cohort study in Germany (PASSOS-Heart Study).

Purpose: In breast cancer patients treated in the 1970s and 1980s, radiation therapy (RT) for left-sided tumors has been associated with an elevated risk of cardiac mortality. In recent years, improved RT techniques have reduced radiation exposure of the heart and major coronary vessels, but some exposure remains unavoidable. In a retrospective cohort study, we investigated the long-term cardiac mortality risk of breast cancer survivors treated with modern RT in Germany.

Methods: A total of 11,982 women were included who were treated for breast cancer between 1998 and 2008. A systematic mortality follow-up was conducted until December 2012. The effect of breast cancer laterality on cardiac mortality and on overall mortality was investigated as a surrogate measure of exposure. Using Cox regression, we analyzed survival time as the primary outcome measure, taking potential confounding factors into account.

Results: We found no evidence for an effect of tumor laterality on mortality in irradiated patients (N = 9058). For cardiac mortality, the hazard ratio was 0.94 (95% CI 0.64-1.38) for left-sided versus right-sided tumors. For all causes of death, the hazard ratio was 0.95 (95% CI 0.85-1.05). A diagnosis of cardiac illness prior to breast cancer treatment increased both cardiac mortality risk and overall mortality risk.

Conclusions: Contemporary RT seems not to be associated with an increased risk of cardiac mortality or overall mortality for left-sided breast cancer relative to right-sided RT. However, an extended follow-up period and exact dosimetry might be necessary to confirm this observation.