Clinical significance of microsatellite instability in endometrial carcinoma

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Abstract
BACKGROUND The purpose of this study was to compare the clinical characteristics of endometrial carcinomas with and without microsatellite instability (MSI). METHODS The authors prospectively acquired DNA from patients with endometrial carcinomas at Washington University Medical Center. Tumors were assigned MSI (+) status when two or more of five microsatellite repeat markers revealed novel bands in tumor DNA not present in the corresponding normal DNA. Clinical characteristics and survival data of patients with and without MSI were abstracted from patient charts. Statistical significance was calculated with the chi‐square test, and survival was assessed with Kaplan–Meier methods. RESULTS The authors found 65 of 70 (93%) patients with MSI (+) tumors to be of white race, whereas only 124 of 159 (78%) patients with MSI (−) tumors were white (P = 0.012). Advanced disease (International Federation of Gynecology and Obstetrics Stage III–IV) was observed in 9 of 70 (13%) MSI (+) patients and 44 of 159 (28%) MSI (−) patients (P = 0.017). In addition, aggressive histologic subtypes were observed less frequently in MSI (+) tumors (6/70 [8%]) than in MSI (−) tumors (30 of 159 [19%]) (P = 0.034). Race and stage were shown by multivariate analysis to be different in MSI (+) and MSI (−) patients. Recurrence and overall survival were similar in the two groups. CONCLUSIONS Patients with MSI (+) tumors were more likely to be of white race and to present with early stage disease. Further investigation is needed to explain why patients with MSI (+) tumors have similar survival to patients with MSI (−) tumors, despite presenting at earlier stages, being of white race, and being less likely to be associated with virulent histologic subtypes. Cancer 2000;89:1758–64. © 2000 American Cancer Society.