Diagnostic challenges in primary pulmonary follicular dendritic cell sarcoma: 2 case reports

To explore the clinical and pathological characteristics and the diagnosis and differential diagnosis of primary pulmonary follicular dendritic cell sarcoma (FDCS).

Clinical and pathological data from 2 cases of primary pulmonary FDCS were collected, and sections were prepared for haematoxylin-eosin (H&E) staining, immunohistochemistry (IHC) staining, and in situ hybridization (ISH). The relevant literature was reviewed. In both cases, the lesions presented as pulmonary masses.

The tumour cells demonstrated diffuse sheets, delicate eosinophilic cytoplasmic staining, oval nuclei and small nucleoli, and occasionally showing multinucleated or giant cells in some areas. Another important histological feature was the abundant infiltration of small lymphocytes among the tumour cells. The tumourcells were positive for one or more follicular dendritic cell (FDC) markers, including CD21, CD23, CD35 and podoplanin (D2-40). ISH revealed negative EBER expression. Both patients underwent surgical resection, and no recurrence or metastasis was observed.

FDCS has a unique histological morphology and immunophenotype for FDCS. It is rare for FDCS to occur in the lungs. However, owing to the lack of experience among doctors and the limitations of small biopsy specimens, FDCS can easily be misdiagnosed as lung cancer. When tumour cells exhibit the above histological features, additional immunostaining for FDC markers should be performed. The Clinical Trial Number is ChiCTR2400090730 and Reg Date is October 12, 2024.