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Other Rare and Unclassified Renal Carcinomas

Image A

Image B

Thyroid-like follicular carcinoma of the kidney

  • Exceedingly rare, resembles well-differentiated thyroid follicular tumors.
  • Characterized by tumor follicles filled with inspissated colloid-like materials.
  • All cases negative for thyroid markers (thyroglobulin- and TTF1-); metastatic thyroid primary carcinoma should be excluded before making the diagnosis.

Unclassified Renal Carcinomas

  • Primary renal carcinoma that does not fit to any of the known RCC types.
  • Mixture of RCC types (image A). (Except low-grade clear cell papillary RCC and TFE3 carcinoma with mixed clear cell and papillary growth).
  • Renal carcinoma with florid or pure sarcomatoid change that the original tumor is no longer identifiable (image B).