BACKGROUND Desmoid tumor (DT), also known as aggressive fibromatosis or desmoid-type fibromatosis, is a rare disease. It can occur in anyone at any age, and is more likely to appear in female patients. DTs are sometimes associated with familial adenomatous polyposis and rare syndromes such as Gardner syndrome. Arising from specific cells, fibroblasts, they tend to develop in patients with a history of abdominal surgery and rarely produce metastases. CASE REPORT We present a case of a 41-year-old man who was referred for abdominal discomfort with no digestive or general symptoms. An abdominal CT scan revealed a mass in the left hypochondrium, corresponding to an intraperitoneal tumor extending to left colon. Based on MRI, we suspected a gastrointestinal stromal tumor. Colonoscopy showed no intraluminal tumor in the colon. A PET-CT scan revealed tumor hypermetabolism and no metastases. The mass was diagnosed as a DT after percutaneous biopsy. Six weeks after diagnosis and as the tumor continued increasing despite pharmacological treatment, the patient underwent surgical pancreatic tail resection with splenectomy and left colonic segmentectomy. Histological examination revealed a 7.047-g DT with severe infiltration of pancreatic parenchyma and transmural colic barrier, with no high-grade differentiation and negative resection margins. The postoperative recovery was uneventful, and we proposed surveillance with MRI. CONCLUSIONS The DT was surgically removed and patient remains under MRI surveillance. Other reported management approaches consist of radiotherapy, tyrosine kinase inhibitors, anti-hormonal therapies/non-steroidal anti-inflammatory drugs, chemotherapy, or close surveillance only. This is, to our knowledge, the largest and heaviest DT reported in the modern literature.