Castleman disease coexisting with papillary thyroid carcinoma: A case report.

Castleman disease (CD) is a rare lymphoproliferative disorder of unknown etiology characterized by lymph node enlargement. CD cannot be confirmed by preoperative puncture cytology, and definitive diagnosis depends on postoperative histopathology. Due to the lack of characteristic clinical manifestations and imaging features, in clinical practice, CD is often easily missed or misdiagnosed, and it is frequently mistaken for lymphoma or autoimmune diseases. Cases of CD that coexist with papillary thyroid carcinoma (PTC) are particularly rare and are often misdiagnosed as PTC with lymph node metastasis. The present study discusses the diagnosis, treatment process and prognosis of a case involving PTC that is complicated with unilateral, single-center CD. This patient was diagnosed with a right lobe nodal gland of the thyroid gland combined with a mass in the left supraclavicular fossa. The postoperative pathological examination revealed a right lobe papillary carcinoma of the thyroid gland with metastasis of the right cervical lymph node combined with CD in the left supraclavicular fossa. The immunohistochemical results of the right cervical lymph node were thyroglobulin (+), thyroid transcription factor-1(+). Immunohistochemical results of left supraclavicular fossa mass: Bcl-2 (low expression in the germinal center, high expression outside), Bcl-6 (germinal center +), Cyclin D1 (-), cluster of differentiation 38 (focally+). In future clinical practice, when encountering PTC with mediastinal masses, clinicians should consider not only common lymph node metastases but also the possibility of CD. Overall, this study aims to provide valuable insights and experience for clinicians regarding CD and PTC.