Clear cell sarcoma

Clinical features

• Malignant mesenchymal neoplasm
• Rare renal tumour (3-5% of all paediatric kidney tumours)
• It occurs almost exclusively between the ages of 6 months and two years
• Male predominance
• Not associated with malformations or syndromes
• Propensity for bone (skull) and visceral metastasis
• Single-centre tumour
• High-risk tumour (SIOP-2001 revised working classification of renal tumours of childhood)

Fig 9a – Clear cell sarcoma of the kidney- Cords of polygonal cells. Remark the chicken wire vasculature (H&E)

• Variable cellularity
• Background with metachromatic mucoid-like material rich in glycoproteins, seen in Giemsa-stained slides
• Large cells that are dispersed or in perivascular pattern
• Round, oval or short spindle bland nuclei with vesicular chromatin
• Nuclear grooves sometimes present
• Inconspicuous nucleoli
• Fragile and pale cytoplasm
• Myxoid stroma may be present
• Necrosis
• The presence of confounding renal tubules entrapped by the tumour that can appear in the smears, can lead to erroneous diagnosis of Wilms´ tumour (these tubules are CD56(NCAM) negative and EMA positive

Immunocytochemistry

• Vimentin: positive, but moderate not strong- “ ….a strong positive Vimentin  points away CCSK”
• CD56 (NCAM)-positive (diffuse)
• CD99: negative
• CD117 :positive
• Bcl2: positive
• EMA: negative
• Desmin: negative
• CD10:negative (rare cases reported as positive)
• CD15:negative
• WT1: negative

Differential diagnosis

• Nephroblastoma (blastemal type)
  • Regular nuclei with fine chromatin
  • Cytoplasm is very scarce (cells in CCS bare more cytoplasm)
  • Sometimes epithelial markers can show poorly differentiated or isolated cells with epithelial differentiation
  • WT1: Positive
• Mesoblastic nephroma
  • Generally diagnosed within the first six months of life
  • Bland, small spindle cells
  •  CD56 (NCAM): negative
  • WT1: positive (cytoplasm)
• Neuroblastoma
  • Nuclei with salt-and-pepper chromatin
  • Neuroblasts at different stages of maturation
  • Fibrillary matrix
  • Vimentin: usually negative
  • Synaptophysin: positive
  • NSE: positive
• PNET
  • Most common in young adults
  • Nuclei with coarse chromatin
  • CD99: positive
  • t (11:22) (q24; q12)
• Rhabdoid tumour
  • Cells with a rhabdoid-like pattern:
    • Prominent eosinophilic nucleoli
    • Eosinophilic para nuclear cytoplasmic inclusions
    • Cytokeratin’s: positive
    • CD56(NCAM): negative
    • INI 1: negative

Main points

• Undifferentiated sarcoma, nearly exclusively in the kidneys
• No familial specific malformations, syndromes or genetic abnormalities associated
• Poor prognostic changes: necrosis
• Even low-stage tumours have poor prognosis
• Also known as bone-metastasizing renal cell tumour
• Metastasis can occur 3 to 10 years after diagnosis
• Recurring genetic defects have been reported:  t(10;17), del(14)(q24.1q31.1)