Microscopic description and IHC:

The biopsy shows tightly packed cells with clear cytoplasm arranged in branched papillary configuration. The individual cells show low grade nuclear morphology (Fuhrman grade 1-2) and the nuclei are arranged away from the basement membrane. The cells are positive for CK7 and carbonic anhydrase IX. They are negative for CD10 and AMACR.

Discussion:

Soon to be known as Tubulopapillary carcinoma.

Better prognosis, less likely to metastasize when compared to clear cell RCC.

No known molecular or genetic mutations.

Characteristic features on H&E:

- Clear cytoplasm

- Apically or centrally oriented nuclei

- Arranged in a papillary, tubular, or acinar pattern

- Low grade nuclei

- No “macrophage islands” or necrosis

Characteristic immunohistochemical staining profile:

- Ca IX positive (characteristic “cupping” pattern)

- CK7 positive (usually diffuse and strong)

- AMACR/racemase negative

- CD10 negative

Tubulopapillary carcinoma table
References:

Gill S., Kauffman E., Kandel S., et al. Incidence of Clear Cell Papillary Renal Cell Carcinoma in Low-Grade Renal Cell Carcinoma Cases: A 12 Year Retrospective Clinicopathologic Study from a Single Cancer Center. International Journal of Surgical Pathology. 2015 Oct 27: 1-6.

CASE IMAGES