Shared chromosome 21q loss in a mixed subtype renal cell carcinoma: composite or collision tumor?

Abstract

Clear cell renal cell carcinoma (CCRCC) and papillary renal cell carcinoma (PRCC) are the two most frequentlyencountered subtypes of renal cell carcinoma (RCC). Rarely, these two entities are identified intermingled within thesame mass and have been labeled either collision tumors juxtaposed by random chance or composite tumors thathave arisen from a common tumorigenic precursor cell. Regarding this distinction, authors have commonly reliedupon macroscopic, histologic, and clinicopathologic findings, which may be prone to subjectivity. Objectivemolecular evidence has been lacking. We present a renal tumor showing a mixed CCRCC and PRCC withcorroborating histologic, immunophenotypic, chromosomal microarray analysis (CMA), and next-generationsequencing (NGS) analysis for the respective tumor components, including classic findings of chromosome 3p lossand VHL mutation within the CCRCC component and gain of chromosomes 7 and 17 within the PRCC component.Of novel interest, CMA revealed a shared loss of chromosome 21q in both components with no other identifiableshared or overlapping mutations. This report adds unique evidence supporting the possibility of a true compositerenal cell carcinoma composed of two commonly recognized subtypes. This finding may help to inform earlymolecular pathogenetic mechanism of RCC tumorigenesis.