Concurrent Interdigitating Dendritic Cell Sarcoma and T-Lymphoblastic Leukemia/Lymphoma: A Case Report and Review of Literature

Interdigitating dendritic cell sarcoma (IDCS) is a rare tumor that arises from classical dendritic cells within the bone marrow. Typically, it is observed subsequent to the development of low-grade B-cell lymphoma. However, there has been only one documented case following T-acute lymphoblastic leukemia/lymphoblastic lymphoma (T-ALL/LBL). The presence of these synchronous tumors with a clonal relationship, indicating a potential transdifferentiation of the tumor. We report a case of concurrent IDCS and T-ALL/LBL. A middle-aged male presented with painful cervical node enlargement. Biopsy revealed parafollicular proliferation of pleomorphic epithelioid cells expressing S100. Immunohistochemistry excluded alternative dendritic cell tumors and melanoma, confirming IDCS diagnosis. Four months post-treatment, generalized lymphadenopathy emerged, revealing small immature T cells clustering amidst IDCS cells in both lymph nodes and bone marrow. Genetic analysis identified NRAS mutation in IDCS but not in T-ALL/LBL, whereas TCR gene rearrangement was detected in T-ALL/LBL but absent in IDCS. Unfortunately, we lack conclusive evidence regarding the clonal relationship or transdifferentiation between these two tumors. They could be unrelated and incidentally develop at the same time.