Yesterday was a fun day on #GUPath. PGY1s, how many of these renal cell tumors can you name? 
The oncocytic one is strongly and diffusely CK7+. What does this help differentiate it from?
Oncocytoma. Both chromophobe and oncocytoma are associated with Birt-Hogg-Dubé syndrome, an AD syndrome where you get papular fibrofolliculomas of face, neck, and trunk as well as multiple oncocytic RCCs. It is associated with 17p12q11 abnormality involving folliculin protein.
This papillary one can be one of two types, which is it? How big does this lesion need to be so we don't call it a papillary adenoma?
Papillary renal cell carcinoma type 1. Papillae are lined by a single layer of cells with low nuclear grade. Foamy macrophages are present in papillary cores. Tumors can have +7, +17, and MET mutations. Needs to be greater than 0.5 cm.
Papillary renal cell carcinoma type 2 has large cells with abundant eosinophilic cytoplasm, spherical nuclei with prominent nucleoli. Nuclei can be pseudostratified. Macrophages are less frequent.
How would you differentiate papillary RCC from clear cell papillary RCC by IHC?
Although morphology is telling, papillary RCC is CD10+ while clear cell papillary is CD10-. Note the clear cell papillary RCC should have nuclei arranged away from fibrovascular cores...which is mostly seen here. CAIX staining is "cup-like."
This last one is clear cell RCC. Grossly this tumor is yellow because of lipid accumulation in tumor cells. If this RCC was 8cm but extended into the vena cava (but below the diaphragm) what T-stage is it?
Thanks for all who answered so far. By size alone, you would grade this as a T2a. However, invasion into the vena cava (but below the diaphragm) makes this a T3b.
