Which of the following is NOT included in the IHC panel for primary RCC?

• A. CK7
• B. PAX8
• C. CD10
• D. CAIX

Answer: (A)

Immunohistochemistry for primary RCC aims to confirm renal origin and help distinguish subtypes. PAX8 is a sensitive nuclear marker for tumors of renal origin and supports RCC. CD10 is commonly expressed in RCC and helps reinforce the diagnosis, though it’s not entirely specific. CAIX shows strong, membranous positivity in clear cell RCC and is a key marker to separate it from other subtypes. CK7, while useful for differentiating subtypes (papillary and chromophobe often show CK7 positivity, clear cell tends to be negative), is not part of the core panel used to establish a primary RCC diagnosis because its expression is variable and less specific. So CK7 is the one not included in the standard IHC panel for primary RCC.