title: A rare case of primary clear cell sarcoma of the pubic bone resembling small round cell tumor: an unusual morphological variant.
abstract: BACKGROUND
  Clear cell sarcoma (CCS) and malignant melanoma share overlapping immunohistochemistry with regard to the melanocytic markers HMB45, S100, and Melan-A. However, the translocation t(12; 22)(q13; q12) is specific to CCS. Therefore, although these neoplasms are closely related, they are now considered to be distinct entities. However, the translocation is apparently detectable only in 50%-70% of CCS cases. Therefore, the absence of a detectable EWS/AFT1 rearrangement may occasionally lead to erroneous exclusion of a translocation-negative CCS. Therefore, histological assessment is essential for the correct diagnosis of CCS. Primary CCS of the bone is exceedingly rare. Only a few cases of primary CCS arising in the ulna, metatarsals, ribs, radius, sacrum, and humerus have been reported, and primary CCS arising in the pubic bone has not been reported till date.
  
  
  METHODS
  We present the case of an 81-year-old man with primary CCS of the pubic bone. Histological examination of the pubic bone revealed monomorphic small-sized cells arranged predominantly as a diffuse sheet with round, hyperchromatic nuclei and inconspicuous nucleoli. The cells had scant cytoplasm, and the biopsy findings indicated small round cell tumor (SRCT). Immunohistochemical staining revealed the tumor cells to be positive for HMB45, S100, and Melan-A but negative for cytokeratin (AE1/AE3) and epithelial membrane antigen. To the best of our knowledge, this is the first case report of primary CCS of the pubic bone resembling SRCT. This ambiguous appearance underscores the difficulties encountered during the histological diagnosis of this rare variant of CCS.
  
  
  CONCLUSIONS
  Awareness of primary CCS of the bone is clinically important for accurate diagnosis and management when the tumor is located in unusual locations such as the pubic bone and when the translocation t(12; 22)(q13; q12) is absent.
authors.affiliation: Department of Internal Medicine I, Osaka Medical College, 2-7 Daigakumachi, Takatsuki City, Osaka 569-0801, Japan. in1304@poh.osaka-med.ac.jp
authors.forename: Shoko
authors.initials: S
authors.lastname: Nakayama
authors.forename: Taiji
authors.initials: T
authors.lastname: Yokote
authors.forename: Kazuki
authors.initials: K
authors.lastname: Iwaki
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Akioka
authors.forename: Takuji
authors.initials: T
authors.lastname: Miyoshi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Hirata
authors.forename: Ayami
authors.initials: A
authors.lastname: Takayama
authors.forename: Uta
authors.initials: U
authors.lastname: Nishiwaki
authors.forename: Yuki
authors.initials: Y
authors.lastname: Masuda
authors.forename: Motomu
authors.initials: M
authors.lastname: Tsuji
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Hanafusa
mesh_terms: D000369:Aged, 80 and over; D058405:Desmoplastic Small Round Cell Tumor / Q000175:diagnosis* / Q000378:metabolism; D003937:Diagnosis, Differential; D006801:Humans; D007150:Immunohistochemistry; D058965:MART-1 Antigen / Q000378:metabolism; D008297:Male; D008545:Melanoma / Q000175:diagnosis / Q000378:metabolism; D058950:Melanoma-Specific Antigens / Q000378:metabolism; D011630:Pubic Bone / Q000378:metabolism / Q000473:pathology*; D009418:S100 Proteins / Q000378:metabolism; D018227:Sarcoma, Clear Cell / Q000175:diagnosis* / Q000378:metabolism; D018228:Sarcoma, Small Cell / Q000175:diagnosis* / Q000378:metabolism; D058951:gp100 Melanoma Antigen
chemical_list: D058965:MART-1 Antigen; D058950:Melanoma-Specific Antigens; C548637:PMEL protein, human; D009418:S100 Proteins; D058951:gp100 Melanoma Antigen