Small Number of Second Cancers Linked to Radiotherapy
Relative risk highest for organs receiving more than 5 Gy radiation, but outweighed by benefits
WEDNESDAY, March 30 (HealthDay News) -- Only a small proportion of second cancers are attributable to radiotherapy for primary tumors in adults, according to a study published online March 30 in The Lancet Oncology.
Amy Berrington de Gonzalez, D.Phil., from the National Cancer Institute in Bethesda, Md., and colleagues estimated the proportion of second cancers attributable to radiotherapy from 15 cancer sites routinely treated with radiotherapy. The study cohort comprised 647,672 adult cancer five-year survivors, aged 20 years or older, from the U.S. Surveillance, Epidemiology, and End Results cancer registries who were treated with radiotherapy for a first primary invasive solid cancer. The relative risks (RR) of second cancers were compared for patients treated with radiotherapy and those not treated with radiotherapy.
The investigators found that the RR of developing a second cancer associated with radiotherapy at the primary cancer sites ranged from 1.08 for cancers of the eye and orbit to 1.43 for cancer of the testes. Organs receiving more than 5 Gy of radiation had the highest RR, which increased with time since diagnosis and decreased with increasing age at diagnosis. Only 8 percent of the total excess second cancers in all radiotherapy patients (at least one year survivors) were related to radiotherapy. For every 1,000 patients treated with radiotherapy, five excess cancers developed by 15 years.
"Even if current practice substantially changed radiation doses to some organs, the general message remains unchanged: the second cancer risks from radiotherapy in adulthood are relatively small, especially when compared with the treatment benefits," the authors write.