The proportion of second cancers related to radiotherapy treatment for the first cancer in adulthood is small (about 8%), concludes an article published in The Lancet Oncology. The findings, from the first study to quantify the risk from routine radiation therapy for multiple first cancers*, suggest that most second cancers are due to other factors such as lifestyle and genetics.

With improvements in cancer survival, determining the long-term risks from treatments such as radiotherapy has become important. It is well established that radiotherapy treatment is associated with a risk of developing a second cancer, but until now, what proportion of second cancers might be related to radiotherapy was not known.

In this study, Amy Berrington de Gonzalez from the National Cancer Institute, Rockville, MD, USA and colleagues collected data on 647 672 adult cancer survivors (who survived for 5 years or longer) from the US Surveillance, Epidemiology and End Results (SEER) cancer registries. They calculated the long-term risk of second cancers from the radiotherapy treatment of first solid-cancer sites in these adults during a follow-up period of 30 years.

During the follow-up period (1978–2007), 9% (60 271) of the 5-year survivors developed a second solid cancer.

The researchers estimated that 8% (about 3300) of these second cancers could be related to radiotherapy treatment for the first cancer. More than half of these were in breast and prostate cancer survivors.

The estimated proportion of second cancers related to radiotherapy varied according to the site of the first cancer—from 4% for cancers of the eye and orbit to 24% for cancer of the testicles.

The risk of developing a second cancer was highest for patients treated at a younger age and for organs exposed to higher radiation doses, and increased with longer time from diagnosis.

For every 1000 patients treated with radiotherapy the researchers estimated three excess radiation treatment-related cancers by 10 years after a first cancer diagnosis, and five excess cancers by 15 years. These risks, say the authors, are small compared with the likely treatment benefits.

The authors conclude: "These findings can be used by physicians and patients to put the risk of radiation-related cancer into perspective when compared with the probable benefits of the treatment...[however] Studies of the second-cancer risks from newer radiotherapy treatments such as intensity modulated radiotherapy...are still needed."

*15 solid cancer sites that are routinely treated with radiotherapy were analysed—oral and pharynx, salivary gland, rectum, anus, larynx, lung, soft tissue, female breast, cervix, endometrial, prostate, testes, eye and orbit, brain and CNS, and thyroid.

Source: Lancet Oncology

Article:  http://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(11)70061-4/abstract