New Report: Cancer and CVD After Radiation Therapy

Nick Mulcahy

March 13, 2012

March 13, 2012 — Second cancers and cardiovascular disease (CVD) after radiotherapy are being experienced by "an ever-growing number of cancer survivors," according to the authors of a national report published in the March 7 issue of the Journal of the National Cancer Institute.

The number of cancer survivors in the United States has tripled since 1971 and is currently estimated to be 12 million, say the authors, who are members of an expert committee convened by the National Council on Radiation Protection and Measurements (NCRP).

The survivorship success has been due, in part, to modern therapies. However, these therapies, including radiotherapy, carry with them an increased risk for late adverse events, most notably second malignant neoplasms (SMNs) and CVD.

The NCRP charged its expert committee with reviewing the associations between SMN and CVD and radiation therapy, which 50% of all cancer patients receive.

Part of the challenge of the task was a relative lack of long-term studies on SMNs and CVD in cancer survivors treated with radiotherapy, according to the authors, led by Lois Travis, MD, from the Wilmot Cancer Center at the University of Rochester Medical Center, New York.

"Few reports describe survival after SMN or CVD," they write.

Nevertheless, there is an "increased awareness" of these 2 events happening after radiation, and there is a body of literature on their incidence, say the authors. SMN and CVD are 2 of the "most frequent and life-threatening adverse events associated with radiotherapy," they write.

Certain cancers carry a higher mortality risk from radiotherapy-related SMNs than others, note the authors. "For patients with Hodgkin's lymphoma, testicular cancer, and certain childhood cancers, SMNs have emerged as an important cause of death," they write.

Radiotherapy-associated CVD refers to a wide spectrum of disorders and is most common after "thoracic radiotherapy for Hodgkin's lymphoma and tangential radiotherapy for breast cancer," the authors add.

The development of SMN or CVD somewhat takes away from any treatment success. "For many survivors, the successes of treatment have been offset by the late effects of cancer and its therapy," Dr. Travis explained in a press statement.

But treatment is typically still worth the risks. "It is important to keep in mind that the benefits of both radiotherapy and chemotherapy for many cancers far outweigh the potential risks of serious adverse effects years later," Dr. Travis told Medscape Medical News in an email.

Conclusions

The published report is a condensed version of a much larger and more comprehensive 425-page report, entitled Second Primary Cancers and Cardiovascular Disease After Radiotherapy, which was 5 years in the making.

Professionals practicing radiation oncology need to better understand the risks of these 2 adverse events, suggested Dr. Travis. "It is vital that we develop the best possible long-term risk estimates and prediction models, and that we establish research priorities and identify concrete ways to prevent serious additional health problems among cancer survivors."

She also explained that the risk for these health problems is multifactorial.

"Many complex factors influence the risk of second malignancies and other health issues after cancer treatment, including lifestyle choices such as diet, exercise, and alcohol and tobacco use, as well as genetics, age, and immune system function," Dr. Travis noted.

The expert committee examined 5 big issues related to the secondary health effects of radiation therapy for cancer: state-of-the-art understanding of radiobiology, genomics, types of radiotherapy, the dose–response relationship, and the effect of attendant therapies such as chemotherapy.

Among the 7 principal conclusions laid out in the report are the following:

  • Quantitative estimates of radiation-induced SMNs are based on studies of older regimens but are applicable to risk assessment in terms of organ-specific radiation doses and dose–response relationships.

  • Newer radiation therapy modalities and techniques, including intensity-modulated radiotherapy and protons, result in different organ dose distributions.

  • Computational models to evaluate CVD risk assessment and comparisons with older radiotherapy modalities should be developed, similar to those available for SMNs.

  • Low-dose cardiac exposure has not been convincingly linked to CVD, but is of potential clinical importance because many radiotherapy-treated patients receive low-dose cardiac doses from scatter and collimator leakage.

  • For individual and epidemiologic risk assessment, the effective dose, which is for radiation protection purposes, should not be used. Instead, the organ-specific absorbed dose coupled with the appropriate relative biologic effectiveness for the end point of interest and radiation type (e.g., electrons, protons, neutrons) should be used for risk assessment.

The report was supported in part by grantsw from the National Institutes of Health, the American Lebanese Syrian Associated Charities, and the University of Rochester Medical Center.

J Natl Cancer Inst. 2012;104:357-370. Abstract

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