Synchronous case of follicular lymphoma and Langerhans cell sarcoma in the same lymph node

Langerhans cell sarcoma (LCS) is a very rare histiocytic and dendritic cell neoplasm originating from Langerhans cells. There are case reports of histiocytic and dendritic cell neoplasms synchronously or sequentially observed in patients with malignant lymphoma. We present a case in which LCS and follicular lymphoma (FL) grade 3a were observed within the same lymph node. A 66-year-old male visited our hospital with a general malaise. Pleural effusion and systemic lymph adenopathy were detected. Biopsy of an inguinal lymph node was performed. The lymph node had regions with follicular structure and regions with acidophilic cytoplasm and large proliferating atypical cells. The tumor cells in the regions with follicular structure showed positivity for CD20 and BCL2 consistent with an FL grade 3a diagnosis. The tumor cells in the regions without follicular structure showed positivity for CD1a and S-100 and were consistent with an LCS diagnosis. Both tumor cells showed the positivity of BCL6 split by FISH. PCR detected IgH clonality in DNA collected from each region, and direct sequence analysis of cells from both tumors detected almost identical amino acid sequences. This finding is important for future research on the development of very rare histiocytic and dendritic cell neoplasms.