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A 41-year-old man presented with a 7-month history of episodes of back and abdominal pain associated with nausea, vomiting, and flushing. Immediately following workup with noncontrast abdominal ultrasonography, he experienced intense flushing and vomiting. Subsequent contrast-enhanced magnetic resonance imaging identified a 5-cm thoracic paraspinal mass (Figure, A). Computed tomography–guided biopsy of the paraspinal mass revealed a dense cellular infiltrate on histopathology composed of cells with round nuclei and abundant pale cytoplasm (Figure, B).
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Spine magnetic resonance imaging revealed an unresectable paraspinal mass with neural foramen encroachment and encasement of the aorta (Figure, A). Biopsy findings revealed a monomorphic infiltrate of medium-sized round cells with abundant amphophilic hypogranular cytoplasm (Figure, B), positive for CD117 (also known as KIT), tryptase (serine protease stored in mast cells), and CD2. Bone marrow biopsy demonstrated aggregates of more than 15 mast cells, negative for point variation (formerly mutation) of codon 816 on KIT (KIT D816V), with no evidence of an associated hematologic neoplasm, supporting a diagnosis of systemic mastocytosis (SM).
Mastocytomas typically present as cutaneous lesions in children and are characterized by a clonal proliferation of morphologically unremarkable mast cells that undergo spontaneous resolution at puberty. Mastocytomas in adults are unusual; extracutaneous presentations are exceedingly rare1,2 and should prompt thorough evaluation for SM.
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Corresponding Author: Nima Nabavizadeh, MD, Department of Radiation Medicine, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Mail Code KPV4, Portland, OR 97239-3098 (email@example.com).
Published Online: July 30, 2020. doi:10.1001/jamaoncol.2020.0787
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank the patient for granting permission to publish this information.
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