Many cancer patients treated with radiation therapy are afraid of suffering from a second tumor. Well, it had always been thought that this treatment was associated with a risk of developing a secondary cancer, but until now it was unknown in what proportion. The magazine 'The Lancet Oncology' has published a study of the National Cancer Institute in Rockville (United States) that reveals the mystery: eight percent. Much less than what was believed.

The authors, led by Amy Berrington de González, calculated the long-term risk of secondary cancers arising from radiotherapy at the locations of solid primary tumors of 647,672 patients during a 30-year follow-up period. During this time, nine percent of those who survived five years developed a second, solid cancer.

Of these, the researchers estimated that only eight percent of these secondary cancers could be associated with the radiotherapy treatment of the first cancer. More than half of these cancers occurred in breast and prostate cancer survivors. The estimated proportion of secondary cancers associated with radiotherapy varied according to the location of the first cancer, from four percent in the case of ocular cancers to 24 percent for testicular cancer.

The risk of developing a second cancer was higher in patients treated at a younger age and in organs exposed to higher doses of radiation and increased with the longer time since diagnosis. For every 1,000 patients treated with radiotherapy, the researchers estimated an excess of three cancers associated with radiation treatment in the 10 years following the diagnosis of the first cancer and an excess of five cancers at 15 years. These risks, the authors point out, are small compared to the possible benefits of the treatment.

Among these benefits, we could point out that radiotherapy is used to reduce the size of tumors, either to make them smaller and thus facilitate surgery, or to delay their progression. For this it damages the tumor cells, although it can also cause some damage in healthy cells. In this way it helps to reduce the possible pain associated with cancer, as well as to avoid relapses.

Radiation Therapy for Lung Cancer | Q&A with Russell Hales, M.D. (November 2019).