Multifocal Inflammatory Myofibroblastic Tumor Presenting With Hemorrhagic Shock Due to Duodenal Invasion by a Pancreatic Head Mass: A Case Report.

Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm of intermediate malignant potential. Although typically indolent, IMT can occasionally exhibit aggressive behavior, including distant metastasis or multifocal involvement. Clinical manifestations vary widely according to anatomic location. Gastrointestinal tract involvement has been reported; however, massive gastrointestinal bleeding leading to hemorrhagic shock is exceedingly rare. We present a 56-year-old man who presented with melena and hemorrhagic shock. Imaging demonstrated a pancreatic head mass with duodenal ulceration, along with a pulmonary nodule and multiple renal lesions. Endoscopic hemostasis was unsuccessful, and transcatheter arterial embolization (TAE) achieved temporary bleeding control. The patient subsequently underwent pancreaticoduodenectomy for definitive hemostasis and local disease management. Histopathologic examination of the pancreatic mass demonstrated spindle cell proliferation consistent with IMT and negative immunoreactivity for anaplastic lymphoma kinase (ALK), c-ros oncogene 1 (ROS1), and other relevant markers. Systemic evaluation revealed multifocal disease involving the brain, parotid gland, lungs, heart, liver, pancreatic tail, kidneys, adrenal gland, lymph nodes, and bones. Dynamic contrast-enhanced magnetic resonance imaging (MRI) of the parotid lesion showed gradual, continuous enhancement, consistent with a fibrous-rich lesion. Based on biopsies from multiple sites and the overall clinical course, a diagnosis of multifocal IMT was established. Initial systemic therapy with doxorubicin achieved stable disease at three months. Based on the genomic findings identified following comprehensive genomic profiling, the patient was subsequently enrolled in the DESTINY-PanTumor02 clinical trial and transitioned to treatment with trastuzumab deruxtecan targeting the human epidermal growth factor receptor 2 (HER2) alteration. Our case represents an exceptionally rare presentation of IMT, characterized by life-threatening gastrointestinal bleeding and extensive multifocal dissemination. It illustrates the marked radiologic and clinicopathologic heterogeneity of IMT and emphasizes the importance of comprehensive histopathologic and molecular evaluation to guide management in aggressive disease variants. Close collaboration across cross-disciplinary diagnostic specialties is essential for the assessment and treatment of rare, multi-organ conditions.