Retroperitoneally located first collision tumor of extra-gastrointestinal stromal tumor and inflamatuar myofibroblastic tumor

To the Editor, A collision tumor is the coexistence of two histologically different tumors in the same organ or close anatomical location. Although collision tumors have been reported in many organs, they are very rare in retroperitoneum. 1. In the literature, two cases of collision tumors: liposarcoma with pancreatic adenocarcinoma 2 and monoclonal plasma cell infiltration with schwannoma 3 have been reported in the retroperitoneum (Table 1).To the best of our knowledge, it has not been reported in the literature a collision tumor arising from the association of extra-gastrointestinal stromal tumor (E-GIST) and inflammatory myofibroblastic tumor (IMT). In this study, we present the first case of a collision tumor associated with retroperitoneal E-GIST and IMT in a 60-year-old female patient.