Colonic pleomorphic undifferentiated sarcoma with a leukemoid reaction: case report.

Background: 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. Case description: 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 × 10 Conclusion: 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.