Secondary cancers caused by radiotherapy

Richard Heywood, University of Cambridge School of Clinical Medicine, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 0SP

Radiotherapy is one of the mainstays of treatment for many cancers, and has contributed to greater survival from many cancer types. However, the radiation used can cause genomic damage to normal tissue, leading to the development of secondary tumours. In the International Journal of Cancer, Maddams et al (1) estimate the burden of radiotherapy induced secondary cancers in the UK.

To estimate how many secondary tumours were related to radiotherapy, the authors took the following approach: firstly, using previous data sets, they identified the risk of new cancer formation in cancer survivors versus the general population. Secondly, they calculated how many of these cancer survivors had received radiotherapy. Thirdly, they combined these data in a mathematical model to identify how much of the difference between survivors and the general population was due to radiotherapy.

Using this model, they estimated that 5.6% of second tumours in men, and 8.1% in women, were due to radiotherapy. Half of these radiotherapy induced tumours were in survivors of breast cancer, but the primary cancers with the highest proportion of radiotherapy associated second tumours were Hodgkin’s lymphoma (17.5%) and oral/pharyngeal tumours (17.8%). Overall these radiotherapy associated second cancers accounted for 0.45% of new cancer diagnoses.

These findings provide the first estimation of the burden of second cancers caused by radiotherapy, although there are several assumptions made which mean that the values must be looked at with caution. Nevertheless, they do demonstrate the risk of radiotherapy, particularly in certain subtypes (e.g. Hodgkin’s lymphoma, oral cancer). Although the benefits of radiotherapy still outweigh the risks, it is important to consider these risks when deciding on the management of primary cancers.

References: 

1. Maddams J, Parkin DM, Darby SC. The cancer burden in the United Kingdom in 2007 due to radiotherapy. Int. J. Cancer 2011;129(12):2885-2893.
doi: 10.1002/ijc.26240

Story image from Wikimedia Commons.