Desmoid tumor mimicking cancer recurrence in a patient with colon cancer and Gardner syndrome: A case report.

Gardner syndrome, a subtype of familial adenomatous polyposis, features colorectal polyposis, osteomas and soft-tissue tumors with elevated colorectal carcinoma risk, and abdominal masses in these patients are easily misdiagnosed as malignant recurrence, especially with concomitant bone lesions. We report a 33-year-old female familial adenomatous polyposis patient with a history of surgically treated stage IIIA colorectal adenocarcinoma, who presented with a 3-month abdominal mass. Contrast-enhanced computed tomography indicated a large cystic-solid mass with lymphadenopathy and peritoneal thickening, suggesting recurrence, while magnetic resonance imaging suggested a desmoid tumor and identified bilateral femoral head avascular necrosis. Surgical resection and pathogenic adenomatous polyposis coli gene mutation detection confirmed an abdominal desmoid tumor. This case highlights that Gardner syndrome can induce benign space-occupying desmoid tumors, and for familial adenomatous polyposis patients with bone lesions, combining advanced imaging, histopathology and genetic testing is critical to avoid misdiagnosis and unnecessary interventions for suspected cancer recurrence.