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The risk of second malignancies after treatment for localized prostate cancer.
Abstracts that were granted an exception in accordance with ASCO's Conflict of Interest Policy are designated with a caret symbol (^).
Background: Prostate cancer has an excellent prognosis with a 10-year relative survival of 99.7%. The long survival for this common cancer raises questions about the risk of second primary malignancies after initial therapy for localized disease. Methods: A population-based cohort of 441,504 men diagnosed with prostate cancer between 1992 and 2010 was identified from Surveillance, Epidemiology and End Results Program data (SEER13). Standardized incidence ratios (SIR) were calculated as an estimate of the risk of a second primary malignancy based on the incidence in the general population according to whether or not men received radiation therapy (external beam radiation therapy or EBRT) as their initial treatment for prostate cancer. Only new primary cancers that arose 10 years or more after prostate cancer treatment were considered. Results: Compared to men who were not treated with radiation, men treated with EBRT were significantly more likely than the general population to be diagnosed with rectal (SIRradiation=1.70 versus SIRnoradiation=0.74, p <0.0001) and bladder cancer (SIRradiation=1.42 versus SIRnoradiation=0.76; p<0.0001). Both groups were at reduced risk of second primary malignancy and second solid tumors overall, but the magnitude of the reduction was less among men who received radiation (e.g., for solid tumors SIR=0.72; 95% CI=0.69,0.76 for those treated with EBRT compared to SIR=0.51; 95% CI=0.49,0.52 for those not exposed to radiation). Conclusions: Men who receive ERBT for localized prostate cancer have a significantly increased risk of later diagnoses of bladder and rectal cancer. Although the absolute risk of developing these cancers is small, physicians should discuss this information with patients before decisions are made on primary treatment for localized prostate cancer.