ALK-positive gastric inflammatory myofibroblastic tumor in an adult with familial adenomatous polyposis and diffuse fundic polyposis

Background: Inflammatory myofibroblastic tumor (IMT) of the stomach is extremely rare in adults and exhibits a variable biological behavior that ranges from frequently benign lesions to more aggressive variants. Here we report a case of gastric IMT with lymph node metastasis in an adult who had undergone total colectomy for familial adenomatous polyposis (FAP). Case presentation: A 37-year-old man presented gradual-onset epigastric discomfort; he had undergone total colectomy for FAP 6 years before. The upper endoscopy revealed diffuse polyposis in the body of stomach and a submucosal protruding tumor of approximately 4.5 x 3.5 cm in the gastric angular incisure, appearing like gastrointestinal stromal tumor. Histology after surgery verified the diagnosis of fundic gland polyposis (FGPs) and gastric IMT with lymph node metastasis. Both the primary IMT tissue and its metastatic lesion but not the FGP or FAP tissue were positive for anaplastic lymphoma kinase (ALK) on immunohistochemical staining. Fluorescent in situ hybridization confirmed the existence of ALK rearrangement in IMT tissues. However, the patient exhibited no abnormalities in microsatellite instability or mismatch repair-system components, including MSH6, MSH2, MLH1 and PMS2, in IMT, FGP or FAP tissue. Conclusions: This case allowed for exploring the relationship among IMT, FGP and FAP and indicates that gastric IMT should be considered in the diagnosis of a gastric mass in patients with FAP. ALK may be a useful biomarker in the diagnosis of IMT and its metastatic lesions.