Background: There are only few reports of endometrial cancer arising in patients with uterine malformations. Down's syndrome is characterized by a reduced risk of solid tumors, and there are no reports about its correlation with uterine malformations.
Case: An endometrial adenocarcinoma arising in both horns of a didelphys uterus of a Down's syndrome woman.
Conclusion: Uterine malformations and genetical disorders may cause a delayed diagnosis of gynecological cancers. Gynecological examination in asymptomatic patients and differential diagnosis in abnormal uterine bleeding patients should be considered.