METASTATIC PULMONARY INFLAMMATORY MYOFIBROBLASTIC TUMOR WITH CEREBRAL INVOLVEMENT: DIAGNOSTIC CHALLENGES AND RADIOLOGICAL RESPONSE TO CRIZOTINIB

Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm of intermediate malignant potential, most commonly arising in the lung. Although generally indolent, distant metastases occur in a minority of cases and can generate major diagnostic uncertainty, particularly when the central nervous system is involved. We report the case of a 48-year-old chronic smoker who presented with intracranial hypertension, seizures, and weight loss. Initial contrast-enhanced thoraco-abdomino-pelvic and brain computed tomography (CT) demonstrated a left lower lobe mediastino-pulmonary mass associated with multiple intra- and extra-axial enhancing cerebral lesions, highly suggestive of metastatic disease. Three CT-guided pulmonary biopsies, two surgical pulmonary biopsies, and a stereotactic brain biopsy were non-diagnostic or only suggestive. Definitive diagnosis was achieved only after cerebral metastasectomy, which confirmed IMT on histology and immunohistochemistry. The tumor was ALK-negative by immunohistochemistry, but fluorescence in situ hybridization identified a TFG-ROS1 fusion. The baseline imaging available at our institution was obtained after metastasectomy and before initiation of targeted therapy. Under crizotinib, follow-up CT showed a marked decrease in the number of brain lesions, from four residual lesions to a single residual lesion, with reduction in lesion size, enhancement, and vasogenic edema. The pulmonary mass also partially regressed, with a decrease of its soft tissue component and progressive calcification. This case highlights the diagnostic limitations of repeated biopsy in IMT, the decisive value of surgical sampling when radiological and pathological findings remain discordant, and the central role of imaging in the post-therapeutic assessment of metastatic disease. It also illustrates the biological and therapeutic relevance of ROS1 rearrangement in metastatic IMT.