The risk of ano-genital malignancies in dialysis and transplant patients

The incidence of anogenital malignancies is greatly increased in patients who have received a renal transplant, but this has not been well studied in patients receiving maintenance dialysis. Our aim was to assess the incidence of these malignancies in patients on dialysis and compare these to transplanted patients. The age standardized incidence ratio (SIR) for anogenital malignancies was calculated by comparing the observed number of malignancies to the expected number. The expected number was calculated by multiplying the age specific incidence rates for each malignancy by the person years at risk in 5-year age cohorts. Of 15,820 patients in the Australia and New Zealand data base, 8,215 had received a renal transplant. A total of 39,750 person years at risk were contributed by patients who had received a renal transplant, while 29,276 person years at risk were contributed by dialysis patients who had not received a renal transplant. For dialysis patients, vulval cancer occurred more commonly than expected (2 observed, 0.48 expected) giving a SIR of 4.2 (95% confidence interval = 0.4-11.9). Cervical cancer occurred less commonly with a SIR of 0.74 (95% Cl = 0.07-2.11). No cases of either anal or penile cancer occurred although these are rare tumors, with only 0.13 and 0.23 cases expected respectively. In transplant recipients 44 anogenital malignancies occurred while 4.3 could have been expected. The SIR ranged from 3.3 (95% Cl 1.7-5.8) for cervical cancer to 55.8 (95% Cl 35.8-83.0) for vulval cancer. To investigate the possible effect of chronic uremia before dialysis began, SIR was calculated to include an additional 24 months of observation before dialysis. The result was to increase the SIR of cervical cancer to 1.7 (95% Cl 0.7-3.2) and lower the SIR for vulval cancer to 2.4 (95% Cl 0.3-8.5). We conclude that dialysis patients are not at significantly increased risk of anogenital malignancies although this study had limited power.