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Case 17 - Discussion

Surgical Pathology Case


CK7, 20 EMA, 20
Colloid-iron, 40  



The Key Features

  • Central scar with loose hypocellular fibrous stroma

  • Uniform granular eosinophilic cytoplasm

  • CK7 scattered +, CD117+, Vim-, CD10-, RCC-

  • Colloid iron luminal surface positive

  • EM: numerous mitochondria

Clinical Futures

  • Most common benign solid renal tumor

  • Originate from the intercalated cells of the collecting duct

  • 3-7% of all renal tumor, 2-12% multifocal, and 4-14% bilateral

  • M:F= 2-3:1

  • Mean patient age is 62-68

  • In ~10% of cases, oncocytoma and chromophobe RCC may coexist

Gross Findings

  • Spherical and large. average 7 cm, with a pseudocapsule or no capsule

  • Cut sections, homogeneously tan-pale yellow, mahogany

  • Characteristic fleshy/stellate central scar in 33-54% of cases

  • Necrosis, hemorrhage and calcification may be present.

Microscopic Findings

  • Large monotonous cells, arranged in well-defined small nests, glandular or tubular structures

  • Do not form papillary, sheet or solid nest structure

  • Nuclei: smooth and round, minimal atypia, large nucleoli

  • Granular eosinophilic cytoplasm

  • In some areas, the tumor nests are separated by a loose hypocellular fibrous stroma

Differential Diagnosis




Chromophobe RCC


Mahogany brown +/- central scar

Pale tan-brown, +/- central necrosis


Closely packed nests (periphery) and nests in loose hypocellular stroma; no trabeculae/sheets

Closely packed solid nests;

+/-broad trabeculae/sheets


Uniform, limited atypia

Classic and eosinophilic cells, more atypia


Granular, acidophilic

Granular, acidophilic with perinuclear halos


Uniform, round, degenerative pleomorphism

More pleomorphism, "raisinoid"


None or rare


Colloidal iron

Focal  positivity on lumen surface

Strong and diffuse cytoplasmic positivity


Most cells negative, scattered cells strongly positive

Diffusely, strongly positive





Numerous mitochondria with lamellar cristae;

no microvesicles

Numerous mitochondria with tubulovesicular cristae; interspersed microvesicles

Cytogenetics Occasional loss of chromosomes 1 and X Multiple monosomies

Immunohistochemistry Staining

  • Cathepsin H +, EMA+,  CD117+

  • CK7: most tumor cells negative, only scattered cells strongly positive

  • RCC-, Vimentin-, CD10-

  • Colloid iron staining: focally positive on the lumen surface

Election Microscopy

  • Abundant abnormal mitochondria


  • Losses of chromosome 1 and X chromosomes, deletion of chromosome 14 and a balanced translocation involving 11q13.

Treatment and Prognosis

  • Benign tumors, and the prognosis after total or partial nephrectomy is excellent.



  • AFIP, 4th series

  • Essential of Anatomic Pathology. Liang Cheng. 2nd Edition.