Interdigitating dendritic cell sarcoma of the parotid gland: case report and literature review.

Interdigitating dendritic cell sarcoma (IDCS) is an exceedingly rare neoplasm arising from the antigen-presenting cells of the immune system. We report a case of IDCS occurring in a 69-year-old man who presented to an outside institution with a painless mass in his right parotid gland for several months. He presented to our institution after undergoing a superficial parotidectomy. A diagnosis of undifferentiated neoplasm, favoring poorly differentiated carcinoma, was made at that time. He underwent a total parotidectomy and neck dissection at our institution. Microscopically, the tumor was composed of atypical spindle cells involving the parotid gland and an ipsilateral level III lymph node. Immunophenotypic analysis demonstrated positive staining for S100, fascin, vimentin, and HLA-II. Follicular dendritic cell, lymphoid, epithelial, myoepithelial, and melanoma markers were negative. Taken together, the above features were consistent with IDCS. An IDCS of the parotid gland is extremely rare, with only 2 cases reported in the literature. The unusual location and morphological similarity to follicular dendritic sarcoma and other types of soft tissue sarcomas can be a diagnostic challenge. Awareness of this tumor and the use of appropriate markers are crucial in making the diagnosis. The patient did well postoperatively, and he underwent a complete course of postoperative irradiation to the right parotid and neck.