Clear cell sarcoma of the kidney (CCSK)

  • Definition

    Clear cell sarcoma of the kidney (CCSK) is composed of uniform, small round cells with a clear appearance and evenly distributed fine chromatin separated by a delicate vascular network. (eMedicine)

     

    Essential features

    Typically a male child, half are diagnosed at 2 – 3 years of age
    Many histological variants exist (see below), but the classic histological appearance is nests or cords of small, plump cells separated by networks of delicate vascular septa
    Clear cells occur in only 20% of cases, despite its name
    Immunohistochemistry has limited use: it is usually only positive for vimentin, although Cyclin D1 may be useful (as of 2015, see below)
    The most important drug treatment is Doxorubicin (Adriamycin®)
    Recent molecular advances in CCSK tumorigenesis have implicated the BCOR gene (see below)

  • Gross Images
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    Gross Description
    • Unilateral and unicentric mass with irregular but sharp tumor / kidney interface
    • Large (mean 11 cm); centered in central kidney or medulla
    • Cut surface is homogenous tan / gray or gelatinous and firm with occasional cysts

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    Microscopy Description

    • Classic pattern: nests or cords of small, plump cells separated by network of delicate vascular septa (also called chicken wire capillaries)
      • This pattern is almost always focally present, but other patterns may be present
    • The 8 variant patterns are myxoid (50%), sclerosing (35%), cellular (26%), epithelioid (trabecular or acinar type) (13%), palisading verocay body (11%), spindle cell (7%), storiform (4%) and anaplastic (2.6%) (Am J Surg Pathol 2000;24:4)
    • Anaplasia is defined as nuclear hyperchromasia, atypical mitoses and giant nuclei (Am J Surg Pathol 2000;24:4)
    • Cells may take on a spindle appearance, particularly near the vascular septae, these cells are termed “septal cells” (Zhou: Uropathology, 1st Edition, 2012)
    • Although the border appears sharp at low power, high power reveals subtle infiltration of the cells into the normal parenchyma at the periphery
    • Nuclei have smooth chromatin and appear washed out, similar to papillary thyroid carcinoma
    • Nucleoli are not prominent; rare mitoses
    • Only 20% have clear cells, and origin of clear cells varies per source: the clear nature of the cells is due to intracytoplasmic vacuoles or an extracellular mucopolysaccharide matrix that imparts a clear cell appearance (Bostwick: Urologic Surgical Pathology, 3rd Edition, 2014Zhou: Uropathology, 1st Edition, 2012)
    • Vascular invasion common

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