Induced second cancers after prostate-cancer radiotherapy: no cause for concern?

( he absolute risks of a radiation-induced second cancer mong long-term radiotherapy survivors are not large, typcally a few percent in older patients (1–4). Hence the very eal concern, expressed by Kendal et al. (5) in this issue, hat prostate cancer patients may be unduly influenced in heir treatment decision by unbalanced media reports of econd-cancer risks. It is certainly the responsibility of the adiation oncologist to communicate a balanced assessment f the potential risks, be they shortor long-term, in the ontext of the potential benefits of the treatment. Kendal et al. (5) go on to argue that there is in fact no ood evidence that prostate radiotherapy produces any deectable increase in the risk of rectal cancer, despite the wide ange of doses, from low to very high, to which the rectum s typically exposed during external-beam prostate radioherapy (6, 7). The article by Kendal et al. (5) raises two issues: (1) Is it rue that prostate radiotherapy does not measurably increase he risk of secondary rectal cancer? (2) Why focus only on ectal cancers after prostate cancer radiotherapy? First, is it true that prostate radiotherapy does not meaurably increase the risk of secondary rectal cancer? Cerainly there is evidence, from epidemiologic studies of a ariety of other primary cancer sites, that radiotherapy is ssociated with increased rectal cancer rates; these include rimary cervical cancer (8), ovarian cancer (9), testicular ancer (10), and Hodgkin’s disease (11). Given that the ange of doses to the rectum after prostate radiotherapy (6, ) encompasses those from these other treatments, it would e surprising if the risks of rectal cancer after prostate adiotherapy were significantly lower or less detectable than or all these other treatments. Kendal et al. (5) do not offer a mechanistic explanation or their suggestion that radiotherapy (RT) does not produce significant increase in rectal cancer risks in long-term rostate cancer survivors. Their argument is the following: hey compare rectal cancer rates taken from the SEER ancer registries (12) for prostate cancer survivors divided