To report a case of thoracic SMARCA4-deficient undifferentiated tumor (SMARCA4-UT) presenting as an isolated metastasis to the inferior rectus muscle, highlighting the diagnostic challenges and the rarity of this presentation.
Approach:
Case Presentation: A 60-year-old man with binocular diplopia and ocular pain underwent ophthalmic evaluation, imaging, and surgical excision leading to the diagnosis of SMARCA4-UT.
Key Findings:
The patient had a nodular lesion in the left inferior rectus muscle, initially misdiagnosed as an orbital inflammatory pseudotumor.
Immunohistochemistry confirmed the diagnosis of SMARCA4-UT with loss of BRG1 expression, positivity for cytokeratin and INI-1, and a high Ki-67 index.
The primary lesion was identified in the left upper lung lobe with mediastinal lymphadenopathy and adrenal gland involvement.
Interpretation:
This case represents the first documented instance of thoracic SMARCA4-UT presenting as an isolated metastasis to the inferior rectus muscle.
Limitations:
The initial diagnosis was based on clinical and imaging findings, which may lead to misdiagnosis of atypical orbital lesions.
The patient's severe ocular pain limited detailed characterization of diplopia and ocular motility disturbance.
Conclusion:
SMARCA4-UT should be considered in the differential diagnosis of extraocular muscle masses.
Experts across Baptist Health Herbert Wertheim Cancer Institute and Eugene M. & Christine E. Lynn Cancer Institute will present new radiation oncology research and clinical expertise at the 2026 Annual Meeting of the American Society for Radiation Oncology (ASTRO), September 26-30, 2026, in Boston.
