Modern radiotherapy safe for heart in breast cancer patients

Breast cancer patients see no excess risk of ischaemic heart disease (IHD)-related mortality after radiotherapy (RT) treatment, according to a recent Singapore study.

“There could be several reasons that contributed to our findings. The patients in our study were treated in an era where breast cancer screening, systemic treatment, and RT techniques have progressed,” the researchers said, adding that in their institution, the use of strict cardiac dose constraints and cardiac shielding has long been routine practice.

A total of 14,419 women (mean age 52.9 years) underwent breast cancer treatment from 2000 to 2016 and were included in the present analysis. IHD-related mortality, the principal outcome, was compared between 9,556 women who did and 4,863 women who did not undergo RT. In addition, the effect of radiation laterality on IHD deaths (right: n=4,677; left: n=4,879) was also assessed.

Eighty-two percent of patients were alive by the end of follow-up, 70 percent of whom saw no disease recurrence. Overall, 2,593 patients died. The mortality rates in the non-RT and irradiated groups were 15.8 percent and 19.1 percent, respectively. [Contemp Oncol 2022;26:59-68]

IHD accounted for 6 percent of all mortalities. In non-RT patients, 9.5 percent of deaths were attributable to IHD; meanwhile, 4.2 percent and 4.9 percent of irradiated patients with right- and left-sided tumours, respectively, died of heart disease. Only 10 patients had both IHD and breast cancer as major contributing causes of death.

Multivariable Cox regression analysis revealed that laterality was not significantly associated with IHD-related deaths in RT patients (left- vs right-sided RT: hazard ratio [HR], 0.94, 95 percent confidence interval [CI], 0.564–1.38). Likewise, chemotherapy had no significant impact on the likelihood of IHD deaths (HR, 1.12, 95 percent CI, 0.70–1.79).

Instead, a history of pre-existing IHD appeared to be a significant risk factor for IHD-related deaths both in non-RT (HR, 5.34, 95 percent CI, 1.94–14.70) and irradiated (HR, 4.18, 95 percent CI, 2.41–7.25) patients.

In a separate analysis, the researchers confirmed that among RT-treated patients, left- vs right-breast cancer did not significantly aggravate all-cause mortality risk (HR, 1.03, 95 percent CI, 0.94–1.13), while increasing disease stages did.

On the other hand, both chemotherapy (HR, 0.85, 95 percent CI, 0.75–0.95; p=0.005) and hormonal therapy (HR, 0.74, 95 percent CI, 0.66–0.83; p<0.001) emerged as significant protective factors against all-cause death.

“We noted a higher proportion of IHD-related deaths in the non-RT group versus the irradiated group. This is probably because breast cancer is a competing cause of death in this group of women, given the higher proportion of more advanced breast-cancer disease,” they researchers said.

“Future study directions include a longer follow-up … and a precise dose assessment to characterize radiation doses in the cardiac substructures,” they added.