Contributed by Daniel Geisler, MD and Gabriela Quiroga-Garza, MD
The patient is a female in her 60s who presents with an incidentally detected kidney mass. Computed tomography shows an enhancing 2.0 cm exophytic, solid right kidney mass of the lower pole. She denies any symptoms, smoking history, or family history of urological malignancies. The patient elects to undergo a laparoscopic partial nephrectomy of the mass in lieu of continued surveillance.
The specimen measures 3.0 x 2.0 x 1.2 cm and consists of a well-defined, partially cauterized, enucleated, and encapsulated lesion. A scant amount of apparent normal renal parenchyma is attached. The cut surface shows a well-defined, glistening, tan-red-brown, and rubbery to spongy mass with no obvious necrosis (Figure 1). The lesion abuts both the parenchymal margin and capsular surface, without discrete involvement of either.
The lesion is well-circumscribed with varying papillary and tubulopapillary patterned architecture (Figure 2A-B). The papillae are lined by a single layer of small to medium-sized cells with eosinophilic cytoplasm. The nuclei are generally uniform and ovoid with inconspicuous nucleoli arranged away from the basal aspect of the cell (Figure 2C-D). The scant stroma is composed of hyalinized to loose fibroconnective tissue with focal edematous areas. Tumor necrosis, mitotic figures, lymphovascular invasion, and perirenal invasion are not identified.
Immunohistochemical stains performed on the tumor show CK7 (Figure 3A), GATA3 (Figure 3B), and EMA (Figure 3C) positivity. The tumor cells are negative for vimentin (Figure 3D), renal cell carcinoma antigen, CD10, carbonic anhydrase IX, and CD117. Parvalbumin demonstrates patchy, weak positivity. Ki-67 shows a low proliferation index with less than 1% of tumor cells positive.