Gastrointestinal stromal tumour presenting as a palpable, undifferentiated abdominal mass

Abstract

Background: We present the case of a previously healthy 60-year-old female with a long-standing history of lower abdominal pain radiating to her back, abdominal distension, and weight loss. She had no abnormal gynaecological history, with four normal vaginal deliveries without complications. A normal vaginal and rectal examination was reported. Transvaginal ultrasound showed a 30-week fetal-size mass with a solid wall, minimal vascularity, a homogeneous cystic centre, septations, and clear contents. Baseline bloods reported microcytic anaemia, thrombocytosis, and no acute rise in tumour markers.

Case report: After correcting her haemoglobin levels with four units of packed red cells, a laparotomy was performed by the gynaecologists with suspicion of an ovarian tumour. General surgery was called based on the cystic nature of the mass, and with concerns about seeding. Peritoneal and omental nodes were excised and sent for histology. A gastrointestinal stromal tumour (GIST) was confirmed with strong positivity of both DOG1 and CD34 receptors. A year course of imatinib was started, with serial computed tomography (CT) scans demonstrating mass shrinkage. A resection was performed. A follow-up CT scan two years after the resection showed no peritoneal disease or local recurrence.

Discussion: A palpable, undifferentiated abdominal mass yields several possible differential diagnoses. Although rare, they are the most frequent mesenchymal tumours of the gastrointestinal (GI) tract. Previously, GISTs were considered benign or malignant. Current European Society for Medical Oncology (ESMO) guidelines state that all GISTs are considered malignant and should be treated appropriately. Occurring primarily in the stomach, extraperitoneal GISTs that mimic ovarian tumours have proven extremely rare, as noted by Tonni et al.¹¹ Following a histological diagnosis, GISTs are treated with tyrosine kinase inhibitors as first-line therapy.

Conclusion: Although rare, this case highlights the consideration of a GIST in the differential diagnosis when confronted with a palpable, undifferentiated abdominal mass.