Incidence and histologic features of mixed renal tumors

Guidelines for management of renal cell carcinoma (RCC) incompletely address the implications of mixed renal tumor histology. We investigate the incidence of mixed renal tumors identified at renal surgery and determine the association with pathologic features.

Institutional kidney tumor database was reviewed to identify 536 patients who underwent partial or radical nephrectomy. Clinical, demographic, and pathologic data were collected. A linear fixed effects model and logistic regression determined the association of mixed tumor histology with tumor size, stage, grade, and nephrometry score.

Three hundred and eighteen men and 218 women with a median BMI of 31 and median tumor size of 3.5 cm were included. 469 (87.5%) patients had pathologic kidney cancer with the most common histologies being clear cell carcinoma in 343 (73.1%) patients, papillary in 81 (17.3%) patients, and chromophobe in 25 (5.3%) patients. Twenty (4.3%) patients had mixed tumors on final pathology. Clear cell RCC was the most common primary pathology in patients with mixed tumor histology (n = 14, 75%) with additional primary tumor histologies included papillary and chromophobe. When considering secondary histologies, 85% were coexistent primary renal cancers while 15% (n = 3) were benign renal tumors. No association of mixed tumor histology and adverse pathologic features was noted.

Mixed tumor histology is an uncommon entity that is not associated with adverse features in a solitary renal mass. These results are especially relevant in discussing the role of renal mass biopsy, and provide further evidence that renal sampling is a valuable tool in the appropriate clinical context.