We report a rare collision tumor of a nodule-in-nodule pattern between a clear cell-type carcinoma and a collecting duct carcinoma in a 24-year-old man. Whereas the outer nodule is quite different from the 'conventional renal cell carcinoma (RCC)' with respect to vascularity, the inner nodule is quite distinctive as regards immunophenotype and karyotype results. Karyotyping the latter by means of comparative genomic hybridization (CGH) disclosed gains of chromosome regions in 1q21.2-qter, 5q21-qter, 6q16.3-qter and 17q21.2-qter along with a loss in 1p21-p31.14, 9q31-pter, 11, 13q12-qter, 15q12-qter and 18q21.1-qter. The clear cell carcinoma surrounding the daughter nodule revealed no 3p loss by means of CGH, unlike most cases of conventional RCC that are seemingly associated with poor vasculature. In summary, to our knowledge, this is the first reported case of an unclassified RCC featuring a unique growth pattern composed of a mixed clear cell type without a 3p loss and a variant of CDC with a unique karyotypic alteration.
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