While NF2 mutations may be found in other established renal cell carcinoma subtypes (often as secondary genetic alterations), they are potentially the genetic driver of this distinctive entity. While we have minimal clinical follow-up, one case presented with distant metastasis, progressed, and resulted in patient death. Two carcinomas demonstrated cellular necrosis.

In some carcinomas, focal or predominant areas had a less distinctive appearance two had areas that resembled clear cell renal cell carcinoma, two had high-grade eosinophilic areas, while one had branching tubular architecture that resembled mucinous tubular and spindle cell carcinoma. The stroma was sclerotic in all eight carcinomas, and all eight contained psammoma bodies that were abundant in two. In 6 of 8 carcinomas, the small cells were focally spindle-shaped and unassociated with basement membrane material. In 6 of 8 carcinomas, branching nodules of small cells clustered around basement membrane material within larger acini yielding a distinctive glomeruloid pattern. The smaller cells clustered around basement membrane material similar to the characteristic pattern of the t(6 11) renal cell carcinoma associated with TFEB gene fusions. All cases were biphasic, characterized by larger and smaller carcinoma cells. The neoplasms were all solid with papillary architecture evident in most cases (7/8), while one was only tubular. The carcinomas were predominantly unencapsulated, and all had a rounded, nodular interface with the native kidney. All patients were adults, ranging from 51 to 78 years of age and of cases of known gender six of seven were males. We report eight cases of a distinctive, previously undescribed renal cell carcinoma associated with somatic mutations in the neurofibromin 2 ( NF2) gene.

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