<prompt> Most common tumor of Retro-peritoneum:StromaSarcomaTeratomaRetro-teratoma  <response>: Ans. b SarcomaRef: Bailey and love 26th ed. ch. 61985 One third of malignant tumors that arise in the retroperitoneum are sarcomas, and approximately 15 of soft tissue sarcomas arise in the retroperitoneum. Retroperitoneal sarcomas are malignant tumors arising from mesenchymal cells, which are usually located in muscle, fat, and connective tissues. Retroperitoneal sarcomas have varying clinical courses depending on their histologic subtype and grade. 