The risk of second malignancy in men with prostate cancer treated with or without radiation in British Columbia, 1984–2000

Abstract

Background and purpose: To describe the risk of second malignancy following a diagnosis of prostate cancer, in British Columbia (BC), Canada. To ascertain whether that risk changed with the use of radiation therapy. Methods and materials: All invasive cases of prostate cancer diagnosed from 1984 through to 2000 were retrieved from the BC Tumor Registry. Standardized incidence ratios (SIRs) were calculated from observed and expected numbers as a percentage. Patients were divided into those who received high-dose radiation therapy (≥45 Gy, RT group) and those not treated with radiation (non-RT group). Results: Overall there was no significant difference between observed and expected second cancer rates, SIR=100 (RT group, N=101; non-RT group, N=98, P= n. s.). Individual tumour sites at significantly increased risk ( P<0.01) included bladder (non-RT group, SIR=132), colo-rectal (RT group, SIR=121), pleura (RT group, SIR=228). Other sites of possible significance ( P<0.05) include sarcoma (RT group, SIR=170) and testis (non-RT group, SIR=282). Conclusions: Increased rates of bladder and testis cancers in the non-RT group are likely to be due to increased urologist surveillance and the use of therapeutic orchiectomy. Increased rates of colorectal cancer in those treated with radiation may be either due to surveillance or treatment. Increases in sarcomas in the RT group are probably treatment-related. Overall the increased second cancer risk for those undergoing radiation therapy was 1 in 220.