UNSCEAR Evaluation on Second Primary Cancer after Radiotherapy

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) was established in 1955 by the United Nations General Assembly, with the mandate to evaluate the latest scientific data on levels, effects and risks of exposure to ionizing radiation on humans and the environment; and to provide independent, objective and up-to-date scientific basis for radiation safety. Ionizing radiation has been used to treat cancer for over a century, primarily through external beam technologies, and constitutes approximately 50% of all cancer treatments. Approximately 40% of cured cancer patients received radiotherapy as part of their treatment.

In 2017, the Scientific Committee endorsed a plan to evaluate the incidence of second primary cancer (SPC) following radiotherapy. The aim was to raise awareness in the scientific and medical communities and amongst national authorities of the fact that cancer treatment by radiation, while contributing to the effective treatment of increasing numbers of patients, can involve off-target exposures which may, in some patients, result in SPC several years later.

The Committee’s literature review indicates that between 5% and 15% of cancer survivors may develop a second primary cancer. However, the Committee considered that only a small proportion of these are likely to be attributable to radiotherapy. The Committee’s evaluation has refined the general understanding of how many of these second primary cancers can be attributed to radiotherapy. The absolute numbers depend upon the specific tissues at risk and the radiation doses received during radiotherapy treatment. In view of the significant benefit of radiotherapy, cancer patients should not be dissuaded from undergoing radiotherapy solely based on concerns regarding the possible development of a SPC. Nevertheless, future design and development of radiotherapy should involve dedicated efforts to reduce second primary cancer induction.