Colonic pleomorphic undifferentiated sarcoma with a leukemoid reaction: case report

Undifferentiated pleomorphic sarcoma (UPS) is an aggressive mesenchymal tumor that typically occurs in the extremities or retroperitoneum. Primary colonic involvement is relatively rare, and those accompanied by a leukemoid reaction are even rarer. This case of primary colonic UPS with a significant leukemoid reaction highlights the unique nature of this rare paraneoplastic syndrome, which may mimic hematologic malignancy and delay appropriate surgical intervention. It also contributes new clinical evidence to the literature by indicating that surgical reduction of tumor burden can reverse tumor-associated leukocytosis and support a paraneoplastic mechanism.

A 49-year-old woman presented with a 3-month history of fatigue, poor appetite, and intermittent low-grade fevers. Laboratory evaluation revealed severe anemia (Hb 56 g/L) and extreme leukocytosis (WBC 41.1 × 10⁹/L) with a left shift, indicating a leukemoid reaction. Bone marrow aspiration and flow cytometry excluded hematologic malignancy, showing only reactive granulocytic hyperplasia. Colonoscopy identified a large, irregular, obstructing mass at the splenic flexure. Contrast-enhanced CT confirmed a colonic tumor with local invasion. After multidisciplinary discussion, the patient underwent radical multivisceral resection, which included left hemicolectomy, distal pancreatectomy, splenectomy, and hysterectomy with bilateral salpingo-oophorectomy. Pathological examination confirmed undifferentiated pleomorphic sarcoma. The proximal and distal colonic margins were negative, whereas sarcomatous tissue was found on the pancreatic tail resection margin. Postoperatively, the leukocyte counts rapidly normalized, and the leukemoid reaction resolved completely. The patient had an uneventful postoperative recovery, and the patient was discharged without early complications.

This case underscores that primary colonic UPS can present with a paraneoplastic leukemoid reaction, which may be mistaken for a primary hematologic disorder. When hematologic malignancy is excluded, such a reaction should prompt evaluation for an underlying solid tumor. Multivisceral resection can reduce tumor burden and may reverse paraneoplastic leukocytosis, while margin status remains critical for postoperative management and long-term surveillance. Multidisciplinary collaboration is required for accurate diagnosis and optimal management of these rare and aggressive tumors.