This report presents the case of an 83-year old man with a collision tumor consisting of an inflammatory myofibroblastic tumor (IMT) and adenocarcinoma of the left colon. As the clinical and radiologic features of IMT are non-specific, only the accurate histopathological examination from the left hemicolectomy specimen was diagnostic. Although the prognosis of a colorectal IMT seemed more favorable than in other sites, four months after surgery the patient developed a tumor relapse. Therefore, malignant behavior of IMT could not be totally excluded. Recent studies have demonstrated that a chromosomal rearrangement involving 2p23, the site of the anaplastic lymphoma kinase (ALK) gene, is present in a subset of these tumors. In our patient, tumor cells did not present ALK-1 perinuclear positivity and it could have indicated a less favorable prognosis. The collision of these different entities is extremely rare and this is the first case reported in literature. Further cases of collision tumors with clinical information including their treatment and prognosis are needed.

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