[1079] Metastases to the Kidney: A Clinicopathologic Study of Forty One Cases with an Emphasis on Deceptive Features

Angela J Wu, L Priya Kunju, Jordan Reynolds, Scott Tomlins, Rohit Mehra, Christopher Przybycin. University of Michigan, Ann Arbor, MI; Cleveland Clinic, Cleveland, OH

Background: Metastatic tumors (MTs) to the kidney are rare; our goal was to review our experience with MTs to the kidney with an emphasis on potentially deceptive features.
Design: The clinical, radiologic, morphologic, and immunohistochemical features of all MTs to the kidney between 5/1987 and 8/2012 at our institution were reviewed. Autopsy cases and any cases in which the MT was incidentally found in a nephrectomy were excluded. Only patients who had a known primary diagnosis and a definitive final diagnosis of MT were included.
Results: Forty one cases (13 nephrectomies (N), 26 core biopsies (Bx), 2 FNAs) were included, accounting for an incidence of <1% of renal masses. A primary malignancy was diagnosed, either prior to or concurrently with the MT, in all cases (mean interval between diagnoses = 5.5 y; 0- 21.6 y). The majority (88%) were carcinomas and the most common primary site was lung (20 (49%) including 11 adenocarcinomas, 8 squamous cell carcinomas, 1 small cell carcinoma); followed by breast (5), gynecologic tract (5), head and neck (3), colon (2), prostate (2), testis (1), skin (1), tibia (1) and adrenal (1). A primary renal tumor was suspected clinically and radiologically prior to the Bx/N in 37% of cases. Unusual features included: common unilateral (85%) and unifocal (88%) involvement, lack of other known distant organ metastasis (32%), a long time interval (>10 y) between diagnosis of primary tumor and MT (20%), and in a small subset of cases, lack of a discrete mass (5%), medullary location (15%), and extension into the renal vein (10%). Nearly all of the MTs had an infiltrative growth pattern (98%), associated lymphovascular invasion (78%), and extended beyond the kidney to involve perirenal/sinus fat and/or adjacent organs (71%). The most common diagnostic dilemma was excluding urothelial carcinoma or collecting duct/high grade renal cell carcinoma; however, in occasional cases, a MT from an unusual site mimicked a low grade renal cell carcinoma. Immunohistochemical stains were performed in only 40% of the cases and were confirmatory in all of these cases.
Conclusions: In our experience, MTs to the kidney most commonly present as solitary unilateral masses and in a substantial subset of cases can both clinically and pathologically mimic a primary renal tumor. A high index of suspicion, vigilance in investigating clinical history, and certain morphologic clues such as an infiltrative growth pattern should help avoid misdiagnoses in these rare cases.
Category: Genitourinary (including renal tumors)

Monday, March 4, 2013 11:15 AM

Proffered Papers: Section A, Monday Morning

 

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