Abstract
The number of longβterm cancer survivors in the general population of the UK is substantial and increasing rapidly. Many cancer survivors have been treated with radiotherapy but the likely number of radiotherapyβrelated second cancers has not previously been estimated. We used estimates of the numbers of cancer survivors in the UK at the beginning of 2007, in conjunction with estimates of the relative risk of a second primary cancer associated with previous radiotherapy from the United States Surveillance Epidemiology and End Results (SEER) programme, to estimate the numbers of incident cancers in the UK in 2007 that were associated with radiotherapy for a previous cancer and that may have been caused by it. We estimated that 1,346 cases of cancer, or about 0.45% of the 298,000 new cancers registered in the UK in 2007, were associated with radiotherapy for a previous cancer. The largest numbers of radiotherapyβrelated second cancers were lung cancer (23.7% of the total), oesophageal cancer (13.3%), and female breast cancer (10.6%); 54% of radiotherapyβrelated second cancers were in individuals aged 75 or over. The highest percentages of second cancers related to radiotherapy were among survivors of Hodgkin's disease and cancers of the oral cavity and pharynx and cervix uteri; over 15% of second cancers among these survivors were associated with radiotherapy for the first cancer. These calculations, which involve a number of assumptions and approximations, provide a reasonable, if conservative, estimate of the fraction of incident cancers in the UK that are attributable to past radiation therapy.