Cytogenomics and gene expression in a case of metachronous bilateral renal cell carcinomas with drop metastasis: Resolving a diagnostic dilemma with molecular technologies.

Metachronous bilateral renal cell carcinomas (RCCs) are rare but well known. We present a case of metachronous bilateral RCCs with a ureter orifice metastasis, for which the pathological diagnosis was confirmed with single nucleotide polymorphism microarray (SNP-M) and gene expression assay (GEA). A 53-year-old man presented with a right ureteral obstruction. A cystoscopy showed a large pedunculated tumor emanating from the right ureteral orifice, consistent with a drop metastasis, which was biopsied. He had a history of a clear cell RCC (ccRCC) 1.5 years prior and a right renal pelvic mass found 8 months later. Histologically, the biopsied right ureteral tumor demonstrated sheets of poorly differentiated cancer cells composed of a mixture of spindled and focal clear cell components. The main differential diagnosis was metastatic RCC versus urothelial carcinoma, but the immunohistochemical profile was not contributory. SNP-M revealed a genomic profile consistent with a metastatic ccRCC with loss of chromosome 3p. GEA showed a gene expression pattern consistent with kidney origin. The cytogenomic array also identified chromosome copy number patterns that were shared between both kidney tumors. This finding suggests that both tumors had a common origin, and thus, the metachronous ccRCC in the contralateral kidney represents a metastasis.