COW-2020-48

1.d

1. Clear cell (tubulo) papillary renal cell carcinoma

A radical nephroureterectomy was performed on a male patient in his 70s for a high-grade ureteric urothelial carcinoma. Gross examination of the kidney demonstrated several cortical cysts, each measuring less than 1.0 cm, as an incidental finding. Microscopic examination revealed occasional papillary infoldings arising in the cyst wall, as shown. The cells in these proliferations had clear cytoplasm, and low-grade nuclei polarized away from the basement membranes. Immunohistochemical staining showed diffuse reactivity for CK7 and HMWK (34βE12). CAIX expression was present along the basolateral aspect of the cells, sparing the luminal surfaces (“cup-like”). CD10 was patchy, and AMACR was negative.

The morphologic and immunohistochemical features observed in this case are currently considered diagnostic for clear cell papillary renal cell carcinoma (CCPRCC). However, it has been now well documented that CCPRCC typically exhibits indolent behavior, with only one case documented in the literature with metastatic disease, which however lacked evaluation of the primary tumor. Some other reported cases with adverse behavior involved tumors demonstrating mixed features of clear cell renal RCC and CCPRCC, and likely represent clear cell RCCs.

Therefore, a case, such as the one presented here, is by default labelled “carcinoma”, despite its incidental detection, small size, predominantly cystic features, and very limited and bland papillary proliferation. These types of cases can potentially be labelled at least as “low malignant potential” or even as “benign” (“cystadenomas”). Moreover, the current evidence overall indicates that CCPRCC may be a candidate for reclassification as a tumor of ‘low malignant potential’, or in some instances, as in the illustrated case, even as a benign tumor. Therefore, it is important to use strict diagnostic criteria when diagnosing CCPRCC, and to be cautious when evaluating core biopsies.

Williamson SR, Gupta NS, Eble JN, Rogers CG, Michalowski S, Zhang S, Wang M, Grignon DJ, Cheng L. Clear Cell Renal Cell Carcinoma With Borderline Features of Clear Cell Papillary Renal Cell Carcinoma: Combined Morphologic, Immunohistochemical, and Cytogenetic Analysis. Am J Surg Pathol. 2015 Nov; 39(11):1502-1510.

Dhakal HP, McKenney JK, Khor LY, Reynolds JP, Magi-Galluzzi C, Przybycin CG. Renal Neoplasms With Overlapping Features of Clear Cell Renal Cell Carcinoma and Clear Cell Papillary Renal Cell Carcinoma: A Clinicopathologic Study of 37 Cases From a Single Institution. Am J Surg Pathol. 2016 Feb; 40(2):141-154.

Gupta S, Inwards CY, Van Dyke DL, Jimenez RE, Cheville JC. Defining Clear Cell Papillary Renal Cell Carcinoma in Routine Clinical Practice. Histopathology. 2020 Jan; 76(7):1093-1095.

Zhou H, Zheng S, Truong LD, Ro JY, Ayala AG, Shen SS. Clear Cell Papillary Renal Cell Carcinoma is the Fourth Most Common Histologic Type of Renal Cell Carcinoma in 290 Consecutive Nephrectomies for Renal Cell Carcinoma. Hum Pathol. 2014 Jan; 45(1):59-64.

Elena Cavazzi (PGY4), University of Calgary, elena.cavazzi@albertaprecisionlabs.ca
Kiril Trpkov, University of Calgary, kiril.trpkov@albertaprecisionlabs.ca

Kidney

Clear cell, papillary, cyst, renal