ESTRO 2024 - Abstract Book

S515

Clinical - Breast

ESTRO 2024

undergone radiotherapy for both breasts, individuals lacking a pathological report, and those with incomplete or unclear information in their radiotherapy records. Within this study, we recorded various risk factors of CVD, encompassing hypertension, hyperlipidemia, obesity, smoking habits, chronic kidney disease, diabetes, and pre existing CVD. Major CVD events were specifically defined as instances necessitating medical intervention. The major cumulative incidence of CVD events was calculated with Kaplan-Meier survival analysis while the hazard was calculated with cox proportional hazards.

Results:

We assessed a total of 1,038 patients, of which 996 individuals were included in the analysis with a median follow up of 9.9 years. In which 503 had left breast cancer and 493 had right breast cancer. Notably, within the entire patient group, 677 (67.0%) had no identifiable CVD risk factors, 181 (18.2%) had one CVD risk factor, and 138 patients (13.8%) had two or more CVD risk factors. It's noteworthy that only a small fraction of patients (0.6%) had a history of smoking. Additionally, 96 patients (9.6%) received internal mammary nodal irradiation (IMN-RT). Almost all patients (n=974, 97.8%) underwent systemic chemotherapy, with 923 patients (92.6%) receiving doxorubicin-based treatment, 274 patients (27.5%) undergoing anti-HER2 treatment (primarily trastuzumab)-based regimen, and 251 patients (25.2%) receiving doxorubicin-based treatment and non-concurrent anti-HER2-based regimen. The 10-year overall survival rate was 84.1%, and the primary cause of death was attributed to breast cancer, with no fatalities recorded due to major CVD events. Over a 10-year period, the cumulative incidence of major CVD events was 3.0% at 10 years, and 7.0% at 15 years. The most prevalent major CVD event was heart failure (50.0%), followed by ischemic heart disease (23.3%) and arrhythmia (23.3%). There was no significant difference of 10-year rate of CVD events observed between patients who underwent left-side radiotherapy (3.4%) and those who underwent right side radiotherapy (3.7%, p = 0.649). Patients with two or more CVD risk factors had a significantly higher rate of major CVD events at 10 years compared to those with one CVD risk factor or none (12.5%, 4.8%, and 0.07%, p < 0.0001). Remarkably, among patients with no CVD risk factors, those who received left-side breast radiotherapy had a slightly higher likelihood of developing major CVD events than those with right-side disease (10-year 2.3% vs. 0.0%, p =0.055). Among patients with left-side disease, the use of IMN-RT significantly increased the likelihood of experiencing major CVD events (10-year 7.6% vs. 10-year 1.8%, p = 0.031). We also found the use of doxorubicin based, trastuzumab-based, or both regimens did not significantly impact the occurrence of all CVD events ( p = 0.367) or heart failure ( p = 0.683).

Conclusion:

In Asian breast cancer patients with low CVD risk factors, the overall risk of experiencing major CVD events following adjuvant radiotherapy to both the breast and regional lymph nodes is notably low. The impact of breast radiotherapy on the development of major CVD events becomes more significant, especially in patients devoid of underlying CVD risk factors. Radiation influence for patients who had underlying CVD risk factors is limited. Furthermore, additional internal mammary nodal irradiation to left-side breast cancer, has been associated with a heightened risk of major CVD events.

Keywords: Breast cancer, cardiotoxicity, radiotherapy

References:

1. Darby SC et al. Risk of ischemic heart disease in women after radiotherapy for breast cancer. N Engl J Med. 2013 Mar 14;368(11):987-98.