Radiation, chemotherapy, and biologic agents, both independently and in combination, increase the risk of cardiovascular disease in survivors of childhood cancer; in fact, cardiovascular death has been reported to account for 26% of the excess absolute risk of death by 45 or more years from diagnosis in adults who survived childhood cancers, and is the leading cause of noncancer mortality in select cancers such as Hodgkin lymphoma (HL).[1,2] During the 30 years after cancer treatment, survivors are eight times more likely to die from cardiac causes and 15 times more likely to be diagnosed with congestive heart failure (CHF) than the general population.[3,4] Therapeutic exposures conferring the highest risk are the anthracyclines (doxorubicin, daunorubicin, idarubicin, epirubicin, and mitoxantrone) and thoracic radiation. The risks to the heart are related to cumulative anthracycline dose, method of administration, amount of radiation delivered to different depths of the heart, volume and specific areas of the heart irradiated, total and fractional irradiation dose, age at exposure, latency period, and gender.
The effects of thoracic radiation therapy are difficult to separate from those of anthracyclines because few children undergo thoracic radiation therapy without the use of anthracyclines. However, several reports do allow some segregation of the effects of radiation from those of chemotherapy. Of note, the pathogenesis of injury differs, with radiation primarily affecting the fine vasculature of the heart and anthracyclines directly damaging myocytes.[5,6] Late effects of radiation to the heart include the following:[7,8,9]
- Delayed pericarditis, which can present abruptly or as a chronic pericardial effusion.
- Pancarditis, which includes pericardial and myocardial fibrosis, with or without endocardial fibroelastosis.
- Myopathy (in the absence of significant pericardial disease).
- Coronary artery disease (CAD), usually involving the left anterior descending artery.
- Functional valve injury, often aortic.
- Conduction defects.
These cardiac toxic effects are related to total radiation dose, individual radiation fraction size, and the volume of the heart that is exposed. Modern radiation techniques allow a reduction in the volume of cardiac tissue incidentally exposed to the higher radiation doses. This may translate into a reduced risk for adverse cardiac events.
Increased risk of anthracycline-related cardiomyopathy is associated with the following:[10,11,12,13,14,15,16,17,18,19,20,21,22]
- Female gender.
- Cumulative doses greater than 200 mg/m2 to 300 mg/m2.
- Younger age at time of exposure.
- Increased time from exposure.
Among these factors, cumulative dose appears to be the most significant in regard to risk of CHF, which develops in less than 5% of survivors after anthracycline exposure of less than 300 mg/m2, approaches 15% at doses between 300 and 500 mg/m2, and exceeds 30% for doses greater than 600 mg/m2.[5,12,23,24,25]