Radiation-Associated Endometrial Cancer

OBJECTIVE: To compare prognostic variables and survival of radiation-associated endometrial cancers with sporadic second endometrial cancers. METHODS: Patients with primary cancers of pelvic organs (urinary system, colorectal, cervix, vulva, and vagina) were identified from the Surveillance, Epidemiology, and End Results (SEER) database between 1973 and 2005. Among these patients, those who received pelvic radiation and subsequently developed endometrial cancer formed the radiation-associated endometrial cancers cohort (cases), whereas those who did not receive pelvic radiation but subsequently developed endometrial cancer formed the sporadic second endometrial cancers cohort (controls). Comparisons between radiation-associated endometrial cancers and sporadic second endometrial cancers used chi(2), t tests, Kaplan-Meier, and cox proportional hazards analysis. RESULTS: In 205 radiation-associated endometrial cancer patients and 1,001 sporadic second endometrial cancer patients, the mean age of diagnosis was 65 years and 68 years, respectively (P <.001). The mean latency between primary pelvic organ cancer and second endometrial cancer was 110 months for the radiation-associated endometrial cancers and 77 months for the sporadic second endometrial cancers (P=.03). The lesions in the radiation-associated endometrial cancers cohort (compared with sporadic second endo retrial cancers) were far more likely to be nonendometrioid histology (76.2% compared with 51%, P <.001), poorly differentiated (58% compared with 28%, P <.001), and advanced stage (international Federation of Gynecology and Obstetrics III and intravenously combined) (43% compared with 16%, P <.001). The 5-year survival rate for radiation-associated endometrial cancers and sporadic second endometrial cancers was 27.1% and 57.1%, respectively (P <.001). In multivariable analysis, after controlling for age, race, histology, stage, grade, and treatment, the hazard ratio for death of sporadic second endometrial cancers was 1.4 (95% (CI) 1.2-3.6; P=.002). CONCLUSION: The radiation-associated endometrial cancers carry a grave prognosis because they are more likely to be nonendometrioid, poorly differentiated advanced stage cancers. The longer latency and extensive spread at diagnosis among radiation-associated endometrial cancers may suggest a possible delay in clinical presentation and diagnosis.