[Clinicopathological characteristics and differential diagnosis of interdigitating dendritic cell sarcoma]. 
Objective: To analyze the clinicopathological features and differential diagnosis of interdigitating dendritic cell sarcoma (IDCS).  Methods: The clinical pathological features of 7 IDCS were analyzed.  Among them, the follow-up results of 6 cases were available.  Results: Among the 7 IDCS patients, 4 cases were male and 3 were female.  The age of the patients ranged from 26 to 69 years. Three cases were originated from lymph nodes and 4 cases were originated from skin, stomach, adrenal gland and mesentery, respectively.  Microscopically, the tumor cells presented as fascicular and storiform proliferation and infiltrated by lymphocytes.  The tumor cells were short-spindle or ovoid, with indistinct border of cytoplasm.  The immunohistochemistry results showed that tumor cells were S-100, Vim, CD68 and CD163 positive, and AE1/AE3, EMA, CD117, CD34, Desmin, SMA, CD1α, CD21, CD23, CD35, HMB45, Melan-A, MelanPan and ALK negative. The BRAF mutation and clonal rearrangement of T and B cells were not detected.  Among the follow-up period of 7 IDCS patients, 3 occurred disease progressions.  Conclusions: IDCS is extremely rare with unique pathological features, and its lesion is not limited to the lymph node.  The IDCS patients with extensive lesions may have worse prognose.  The differential diagnosis of IDCS includes other histiocytic and dendritic cell neoplasms, malignant melanoma and soft tissue neoplasms.