Diagnosis

Diagnosis

Low grade oncocytic tumor of kidney.

Discussion

Histological examination revealed an unencapsulated 0.6 cm oncocytic lesion within a grossly described calcified cyst of the right kidney. The neoplastic cells had eosinophilic cytoplasm with round nuclei, and exhibited a nested growth pattern. The nuclear membranes were smooth and regular. Some of the cells displayed vague perinuclear halos, raising the differentials of oncocytoma and chromophobe renal cell carcinoma, eosinophilic variant.

Immunohistochemical investigation showed the tumor cells were diffusely positive for CK7, but lacked expression of CD117. This immunohistochemical profile is inconsistent with renal cell carcinoma (clear cell and chromophobe variants) as well as renal oncocytoma. The lesion was ultimately diagnosed as low grade oncocytic tumor of kidney.

A CD117-negative, CK7-positive oncocytic renal tumor that does not fit within existing diagnostic categories was first described as “low-grade oncocytic tumor of kidney” in 2019 by Trpkov and colleagues. Subsequent retrospective studies of cases that fit these criteria have discovered that this entity shows consistent GATA3 positivity, and is characterized by molecular alterations of TSC1, TSC2, MTOR or PIK3CA.

In recent years, there has been a growing emergence of eosinophilic renal neoplasms with low-grade nuclear features. In arriving at the correct diagnosis, it is important to rule out aggressive features, including extrarenal extension, coagulative necrosis, sarcomatoid differentiation, high-grade nuclear atypia, and lymphovascular invasion. It is also imperative to conduct clinical correlation to ensure the tumor is limited to the kidney. Once an accurate diagnosis of low-grade oncocytic tumor of the kidney has been made, the clinician can orchestrate a management approach based on the generally low risk of progression.

References

Amin, M. B., McKenney, J. K., Martignoni, G., Campbell, S. C., Pal, S., & Tickoo, S. K. (2022). Low grade oncocytic tumors of the kidney: a clinically relevant approach for the workup and accurate diagnosis. Modern Pathology, 35(10), 1306-1316.

Trpkov, K., Williamson, S. R., Gao, Y., Martinek, P., Cheng, L., Sangoi, A. R., ... & Hes, O. (2019). Low‐grade oncocytic tumour of kidney (CD117‐negative, cytokeratin 7‐positive): a distinct entity?. Histopathology, 75(2), 174-184.

Williamson SR, Hes O, Trpkov K, Aggarwal A, Satapathy A, Mishra S, Sharma S, Sangoi A, Cheng L, Akgul M, Idrees M, Levin A, Sadasivan S, San Miguel Fraile P, Rogala J, Comperat E, Berney DM, Bulimbasic S, McKenney JK, Jha S, Sampat NY, Mohanty SK. Low-grade oncocytic tumour of the kidney is characterised by genetic alterations of TSC1, TSC2, MTOR or PIK3CA and consistent GATA3 positivity. Histopathology. 2023 Jan;82(2):296-304. doi: 10.1111/his.14816. Epub 2022 Oct 18. PMID: 36208048.
 

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