Histopathologic results of biopsy specimen of the left supraclavicular mass. (A) Hematoxylin-eosin stained section (×40) revealed that diffuse infiltration of medium to large atypical cells with round nuclei and prominent nucleolus. (B–D) Immunochemistry examination for Mum-1, CD 38, and CD 138 were intensively positive for neoplastic cells (×40). (E) Immunochemistry showed Ki-67 expressed in the nuclei of 80% of neoplastic cells (×40). (F) In situ hybridization revealed negativity for Epstein-Barr virus-encoded small RNA (EBER) (×40).