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Case 359 - Discussion

Uploaded: 2009-10-16, Updated: 2009-10-16

 Clear Cell Sarcoma of Kidney (CCSK)


  • Malignant mesenchymal neoplasm

  • Undifferentiated cells, abundant extracellular matrix, in cords and nests separated by a fine vascular network.

  • A striking predilection to metastasize to bone, "bone metastasizing renal tumor of childhood."


  • 5% of primary pediatric renal tumors;

  • Peak age, 2 years.

  • M:F>2:1.


  • Median weight, 500 - 600 g.

  • Mostly within the renal medulla, irregular and sharply defined, unencapsulated.

  • Homogeneous, light brown or gray, dense, firm texture. Some tumors soft and mucoid.

  • Cysts often present .


  • Undifferentiated plump cells arranged in nests or cords of 6-10 cells in width.

  • "Chicken wire":  evenly dispersed, regularly branching small vessels separating cord cells.

  • Cord cells:

    • Uniform in size, loosely spaced, and have indistinct cell borders. Rarely densely packed or overlapping.

    • Nuclei: finely dispersed chromatin, no prominent nucleoli or chromatin condensation. Frequent "empty"-appearing nuclei.

    • Focally the tumor cells may have condensed and acidophilic cytoplasm.

  • Abundant extracellular, Alcian blue positive, mucopolysaccharide matrix.

  • Tumor boarder: subtly infiltrating the normal renal parenchyma for short distances, nibbling into the adjacent renal parenchyma.

  • Variants:

    • Myxoid pattern,: most common variant, diffuse accumulation of mucopolysaccharide matrix between cord and septal cells.

    • Sclerosing pattern (35%CCSKs): abundant acellular collagen, often limited to the region of cord cells.

    • Cellular pattern ( 25%): close spacing and overlapping of nuclei, decreased intercellular material.

    • Epithelioid pattern (13%):  most often mistaken diagnosis of nephroblastoma. Condensation of the cord cells in ribbons, tubules, rosettes, and trabeculae. The intervening vascular septa usually retained but not always conspicuous.

    • Spindle cell pattern (7%): both the septal and cord cells may have spindle cell features, reminiscent of other soft tissue tumors.

    • Palisading pattern (15%): alignment of spindle cell nuclei in parallel linear arrays, alternating with nuclear free zones.

    • Sinusoidal (pericytomatous) pattern: blood vessels distended, resembling a hemangiopericytoma.


  • Vimentin +

  • Epithelial markers -



Mesoblastic Nephroma

Clear Cell Sarcoma of Kidney


   Age less than 6 months
   Increased renin, calcium

Age more than 1 year
Metastases (except lung)

Light Microscopy

   Classic mesoblastic pattern

Classic CCSK pattern

   Renal dysplasia (e.g., cartilage)

Most variant CCSK patterns

   Coarse chromatin

Fine chromatin

   High mitotic rate

Low mitotic rate

   Extensively infiltrating margins

Grossly well demarcated, microscopically infiltrative

   Staghorn vessels in tumor

Extensive sclerosis

   Tumor surrounds groups of nephrons

 Tumor entraps isolated nephrons


   Positivity for desmin and/or actin

Negativity for desmin and actin



Clear Cell Sarcoma


   Nephroblastoma syndromes
   Bilateral/multicentric tumors

Metastases to bone, brain, or other sites
(except lung, lymph nodes, liver)

Gross and Light Microscopy

   Heterologous cell types (skeletal muscle, etc.)

Classic or variant CCSK patterns

   Classic blastemal patterns (serpentine, etc.)

Homogeneous, pale H&E appearance

   Nodular growth pattern

Tumor surrounds, isolates nephrons

   Botryoid intrapelvic growth

Prominent collagen

   Nephrogenic rests



  WT1+, CD56+, epithelial +, muscle+, or neural +

Vimentin +



  • Bone metastasis is the most common mode of relapse, other commonly metastatic sites are brain, lung, liver, and soft tissue.

  • 6-year survival: 97% stage I; 75% stage II; 77% stage III; and 50% stage IV.


  • AFIP, tumor of the kidney, bladder and related urinary structures, series 4;