OBJECTIVETo study the pathologic features, diagnosis and differential diagnosis of interdigitating dendritic cell sarcoma (IDCS).

METHODSThe clinical findings, morphologic features and immunophenotype of 3 cases of IDCS were investigated.

RESULTSGross examination showed that IDCS had a greyish-white to greyish-yellow cut surface. The site of occurrence included lung, spleen (with lymph node metastasis) and lymph node. Histologically, the tumor cells were arranged in nests, fascicles and whorls, with intimate admixture of many lymphocytes and plasma cells. They were oval to spindle in shape and contained pale eosinophilic cytoplasm, oval and sometimes grooved nuclei, small distinct nucleoli and ill-defined cell borders. Immunohistochemical study showed that the tumor cells expressed S-100 protein.

CONCLUSIONSIDCS is a rare type of histiocytic and dendritic cell malignancy with distinctive morphologic findings. It needs to be distinguished from follicular dendritic cell sarcoma, inflammatory pseudotumor, Langerhans' cell histiocytosis, malignant melanoma, undifferentiated carcinoma and anaplastic large cell lymphoma. Immunohistochemical staining for S-100 protein is helpful in confirming the diagnosis.