FCER2 and Castleman disease: Histopathological examination reveals lymphoid follicular hyperplasia within the affected lymph nodes, characterized by prominent germinal centers and interfollicular vascular proliferation with dense plasma cell infiltration. Based on histomorphology features, Castleman disease is classified into three subtypes: Hyaline vascular type、Plasma cell type、Mixed type. Immunohistochemical analysis demonstrates positive expression of follicular dendritic cell markers (e.g., CD21, CD23), along with variable expression of B-cell markers (e.g., CD20, PAX5) and T-cell markers (e.g., CD3, CD5).