Title : MMR-deficient dedifferentiated endometrial carcinoma with synchronous uterine leiomyosarcoma: A rare collision tumour
Abstract:
Background: Dedifferentiated endometrial carcinoma (DEC) is a rare and aggressive uterine malignancy. Its synchronous occurrence with uterine leiomyosarcoma as a collision tumour is exceptionally uncommon and has important diagnostic and therapeutic implications.
Case Presentation: A 74-year-old postmenopausal woman presented with abnormal uterine bleeding and underwent total abdominal hysterectomy with bilateral salpingo-oophorectomy. Histopathology demonstrated dedifferentiated endometrial carcinoma arising from FIGO grade 1 endometrioid adenocarcinoma together with a spatially distinct uterine leiomyosarcoma, consistent with a true collision tumour. Immunohistochemistry demonstrated subclonal loss of MLH1 and PMS2 in approximately 40% of the dedifferentiated component, while MLH1 promoter hypermethylation confirmed a sporadic epigenetic mechanism. The patient subsequently received adjuvant radiotherapy and chemotherapy and remained in complete clinical remission at one-year follow-up.
Discussion: This case highlights the importance of integrating morphology, immunohistochemistry and molecular diagnostics to distinguish collision tumours from carcinosarcoma and other high-grade uterine malignancies. Subclonal mismatch repair deficiency demonstrates intratumoral heterogeneity and may have implications for molecular classification, prognostication and future immunotherapy.
Conclusion: This rare collision tumour emphasises the importance of multidisciplinary collaboration and comprehensive pathological assessment for accurate diagnosis and optimal management.
