Nature and significance of stromal differentiation in carcinosarcoma (MMMT): unravelling the biology and shifting current paradigms

Carcinosarcoma (CS) is a rare, aggressive malignancy of the Mullerian system often termed mixed malignant Mullerian tumor (MMMT). It is biphasic in nature, differentiating into epithelial and sarcomatous components. Tumor-node-metastasis (TNM) staging and mismatch repair (MMR) status is the basis for both prognostication and therapeutic decision making. However, stromal differentiation (SD) is a new frontier in the field of histopathology and many studies have demonstrated its prognostic significance. The present study is the first study to evaluate the role of SD in carcinosarcoma. Here we found immature SD to be a significant prognostic signature (p = 0.04). It outperformed age, nodal metastasis, and lymphovascular invasion for predicting cancer-free survival. Immature SD also corelated with both myometrial invasion (p = 0.01) and tumor stage (p = 0.02). Carcinosarcoma has been previously thought to have universally poor outcomes; however, mature SD was found to be protective in this cancer subtype. Our findings support the integration of SD into the synoptic reporting for carcinosarcoma; however, this will require pathologists to shoulder the adoption of SD into clinical practice.