The National Council on Radiation Protection and Measurements (NCRP) convened an expert scientific committee to review and make recommendations on the association between radiotherapy and second malignant neoplasms (SMNs) and cardiovascular disease (CVD). It concluded that SMNs and CVD are among the most serious late adverse effects experienced by cancer survivors and their risks should be further evaluated, according to a summary of NCRP's recommendations published in the March 7 issue of the Journal of the National Cancer Institute.
“With the increased awareness of the adverse consequences of cancer therapy, it has become critically important to identify measures to mitigate and ameliorate these late adverse effects and to provide cancer survivors with counseling, surveillance, and supportive care,” wrote Lois B. Travis, MD, of the University of Rochester Medical Center, and colleagues.
The authors of the summary first noted that modern cancer therapies, including radiotherapy, have prolonged the lives of cancer patients. Five-year relative survival rates for all cancers combined reached 66 percent for patients diagnosed between 1999 and 2006, and the number of cancer survivors in the U.S. has tripled since 1971.
This success comes at a cost, according to Travis et al, as radiotherapy, used as a treatment for half of all patients, is associated with SMNs and CVD. The association with SMNs has accrued the most data, with radiotherapy shown to play a role in Hodgkin lymphoma, non-Hodgkin lymphoma and cancers of the cervix, testis, breast and prostate. Radiotherapy-related CVD is the leading noncancer cause of mortality.
Other conclusions from the NCRP include:
- Quantitative estimates of radiation-induced SMNs are applicable to risk assessment following current radiotherapy despite being based on past regimens;
- Low-dose cardiac exposures have not been convincingly linked to CVD, but associations between whole-body doses of less than 1 Gy and CVD shown in atomic bomb survivors are potentially clinically important;
- Few reports describe survival after SMN or CVD; and
- Effective dose should not be used for individual and epidemiological risk assessment.
The NCRP recommends large-scale follow-up of cancer survivors to characterize the risk of SMNs and CVD, according to the authors. Risks of SMNs and CVD should be compared after different radiotherapy modalities, and analytic studies should address the relationship between dose and risk of SMNs and CVD.
“The expanding use of radiotherapy and development of new radiation modalities to treat cancer, coupled with improvements in long-term patient survival, underscores the importance of continuing to provide long-term risk estimates as well as additional research into the molecular underpinnings of treatment-related SMNs and CVD,” wrote the authors.