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Glomerular sparing pattern in primary kidney neoplasms: clinical, morphological and immunohistochemical study.

Glomerular sparing (GS) is defined as a unique growth pattern in which tumor cells replace the majority of renal tubes and overrun intact glomeruli. This phenomenon has been well recognized by pathologists as a typical infiltrative pattern and some studies suggested it was an independent risk factor. Here, we study the clinical, pathological, and immunohistochemical features of primary kidney neoplasms with glomerular sparing pattern. We searched the archives of our pathology department for nephrectomy specimens and reviewed all pathology reports from 2009-2013. We selected cases with tumor and collected clinicopathological information, focusing on re-evaluation of cases with glomerular sparing pattern. To facilitate our study we performed immunohistochemical stains of PAX-8, p63, and InI-1 on selected cases. We selected a total of 204 nephrectomy cases in this study, including 163 cases of renal cell carcinoma; 37 cases of urothelial carcinoma; 4 cases from other categories (Wilms tumor, primary diffuse large B-cell lymphoma, angiolipoma, rhabdoid tumor). Finally, we identified 7 cases of primary kidney tumors with glomerular sparing pattern: 2 cases of clear cell renal cell carcinomas (ccRCC), 1 case of collecting duct carcinoma, 2 cases of urothelial carcinoma (UC), 1 case of diffuse large B-cell lymphoma and 1 case of malignant rhabdoid tumor. The primary kidney tumors with glomerular sparing pattern are rare and incidence in our study is <4% (7/204). There is no specificity for any tumor type, but more commonly seen in high grade UC rather than RCC. It can also be seen in rare neoplasms such as collecting duct carcinoma, lymphoma and malignant rhabdoid tumor. These GS cases need to be recognized as they are often associated with high grade, high stage, large tumor size, and worse prognosis.