Answer and Discussion of Quiz Set: K-004

2.   Which of the followings can be used to differentiate eosinophilic variant of chromophobe renal cell carcinoma from other eosinophilic renal cell carcinomas? Answer

A.  Vimentin (+), C-kit (-), E-cadherin (-), AMACR (-), Pax2 (+)

B.  Vimentin (-), C-kit (+), E-cadherin (+), AMACR (-), Pax2 (-)

C.  Vimentin (+), C-kit (+/-), E-cadherin (+/-), AMACR (+), Pax2 (+)

D.  Vimentin (-), C-kit (+), E-cadherin (+), AMACR (-), Pax2 (+)

Answer and Discussion: The answer is (B).

• Most consistent with clear cell renal cell carcinoma: Vimentin (+), C-kit (-), E-cadherin (-), AMACR (-), Pax2 (+)
• Most consistent with chromophobe renal cell carcinoma: Vimentin (-), C-kit (+), E-cadherin (+), AMACR (-), Pax2 (-)
• Most consistent with papillary renal cell carcinoma: Vimentin (+), C-kit (+/-), E-cadherin (+/-), AMACR (+), Pax2 (+)
• Most consistent with oncocytoma: Vimentin (-), C-kit (+), E-cadherin (+), AMACR (-), Pax2 (+)

The major differential diagnosis for eosinophilic variant of chromophobe carcinoma is oncocytoma. In general, vimentin is positive in most renal cell carcinoma except for oncocytoma and chromophobe renal cell carcinoma. Both eosinophilic variant of chromophobe carcinoma and oncocytoma are negative for vimentin but chromophobe renal cell carcinoma is positive for colloidal iron and and negative for Pax2. Cytokeratin 7 is also a good marker to use. Chromophobe renal cell carcinoma is usually diffusely positive while it is only patchy positive or negative in oncocytoma. Strong cytoplasmic staining with accentuation at the periphery is a feature seen in some chromophobe renal cell carcinoma in contrast to clear cell renal cell carcinoma.

Hale colloidal iron is diffusely positive in the cytoplasm of chromophobe renal cell carcinoma but one must note that this stain can be difficult to interpret. Some eosinophilic variants of chormophobe renal cell carcinoma can be negative.

Numerous small vesicles in cytoplasm. This feature distinguish this eosinophic chromophobe carcinoma from oncocytoma which would contains numerous mitochondria. However, the electron microscope is rarely called for diagnostic purpose for distinguishing these two tumor these days.

Clear cell renal cell carcinoma and papillary renal cell carcinoma can also have extensive eosinophilic changes. However, some histologic evidence without oncocytic changes are often present if the search is extensive enough. In addition, both of them are vimentin positive. Other markers such as CK7, Pax2, AMACR, and C-kit can also help in the differential diagnosis.