Introduction: Endometrial cancer (EC) is the most common gynecologic cancer in the United States. Racial disparities in the incidence and mortality of this cancer are apparent; black women are less likely to develop this malignancy and yet are more likely to die when diagnosed. Racial differences of second primary cancer (SPC) have not been examined, and the goal of this study was to examine these differences.

Methods: With the use of the National Cancer Institute's Surveillance, Epidemiology, and End Results database, SPC risk in white patients and black patients with EC was compared to the general population and to women with other primary cancers. Standardized incidence ratios (SIRs) of SPC (overall and by tumor site) with 95% confidence intervals were calculated. Poisson regression was used to estimate the race-specific risk of SPC in EC cases treated with radiotherapy versus nonirradiated cases.

Results: The analysis included 11,047 patients with EC diagnosed between 1973 and 2007 that developed an SPC. Overall risk of SPC in white women with EC was significantly lower than that in the general population (SIR = 0.85; 95% CI, 0.84-0.87) but significantly higher in black women with EC (SIR = 1.19; 95% CI, 1.08-1.31). White women with EC treated with radiotherapy were more likely to develop SPC compared with nonirradiated cases (incidence rate ratio [IRR], 1.18; 95% CI, 1.14-1.23).

Conclusions: This is the first analysis of race-specific SPC risk in EC cases, and it suggests differences between white women and black women with EC. Although exploratory, these data provide important clues about the etiology of SPC in patients with EC. This analysis also highlights the need for careful monitoring after diagnosis and treatment of EC.