Giant Metastatic Gastrointestinal Stromal Tumor Occupying the Entire Abdominal Cavity Presenting as Transfusion-Dependent Anemia: A Comprehensive Case Report.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract and are usually diagnosed before reaching an advanced size. Giant GISTs exceeding 20 cm are uncommon and are frequently associated with adverse pathological features, including high mitotic activity, necrosis, and metastatic dissemination, which together drive an aggressive clinical course and a poor prognosis. We report the case of a 57-year-old man with type 2 diabetes mellitus who presented with progressive abdominal distension, fatigue, early satiety, transfusion-dependent anemia, and general deterioration. Computed tomography demonstrated a 29 × 20 cm intra-abdominal mass occupying nearly the entire abdominal cavity, without radiologic evidence of major vessel invasion. Given the severity of the anemia and the rapid clinical decline, the multidisciplinary team proceeded directly to exploratory laparotomy without preoperative tissue diagnosis; the rationale for this decision is discussed. Complete macroscopic tumor resection was achieved together with resection of a densely adherent segment of ileum and mechanical side-to-side intestinal anastomosis, but the procedure was complicated by an estimated 3,000 mL of blood loss, attributed to tumor neovascularity and adhesiolysis, requiring massive transfusion. Histopathology confirmed a 30 cm mixed-type GIST weighing more than 5 kg, with diffuse CD117 positivity, a mitotic index of 18/5 mm², focal necrosis, negative surgical margins (R0), and metastatic implants in the omentum and parietal peritoneum, consistent with high-risk metastatic disease without transmural bowel-wall invasion -- a pattern more in keeping with a mesenteric/extraintestinal GIST closely applied to the ileum than a primary transmural ileal tumor. Despite maximal postoperative intensive care, the patient developed refractory distributive shock, severe metabolic acidosis, and progressive multiorgan failure, and died on postoperative day 1. This case illustrates the extreme end of the GIST clinical spectrum and underscores the importance of early diagnosis, prompt referral, and structured multidisciplinary planning, including a deliberate, documented decision process around preoperative biopsy and neoadjuvant therapy, before disease reaches this magnitude.