Definitive Radiotherapy for Unresectable Unicentric Mediastinal Castleman Disease: A Case Report.

Castleman disease is a rare nonclonal lymphoproliferative disorder with heterogeneous clinical presentations and therapeutic approaches. Surgery remains the standard treatment for unicentric Castleman disease, while radiotherapy may represent an alternative option in unresectable cases. We report the case of a 17-year-old female who presented with exertional dyspnea related to a right hilar mediastinal mass. Chest computed tomography revealed a well-circumscribed lesion closely related to adjacent vascular and bronchial structures. Histopathological examination demonstrated abnormal lymphoid follicles with atrophic germinal centers producing the characteristic "onion-skin" appearance. Immunohistochemical analysis showed a CD3-, CD20+, CD21+, Bcl2-, and CD5- profile consistent with the hyaline vascular subtype of unicentric Castleman disease. Positron emission tomography/computed tomography demonstrated localized hypermetabolic mediastinal lymphadenopathy without distant involvement. Due to close vascular relationships and high hemorrhagic risk, the lesion was considered unresectable after multidisciplinary discussion. The patient underwent definitive volumetric modulated arc therapy (VMAT) delivering 39.6 Gy in 22 fractions. Treatment was well tolerated without significant acute or late toxicity. After 13 months of follow-up, clinical and radiological evaluation demonstrated a favorable response, with approximately 50% tumor reduction according to RECIST v1.1 criteria, improvement in dyspnea from New York Heart Association (NYHA) class III to class II, and normalization of pulmonary function tests. This case highlights the potential role of definitive radiotherapy as an effective and well-tolerated therapeutic alternative in unresectable unicentric mediastinal Castleman disease.