The diagnostic criteria and management of renal cell carcinoma (RCC) has evolved significantly in the last two decades. Increased molecular profiling of RCC has yielded further refinement of existing diagnostic categories. This is particularly true for papillary RCC, which has evolved into multiple molecularly distinct entities. Collecting duct carcinoma, on the other hand, continues to be defined based on traditional histology-based criteria, although it is now possible to exclude various categories of tumors that share overlapping morphologic features. In this context, it is important to note that pathology laboratories have varying degrees of access to complex molecular technologies required to profile tumors in routine clinical practice. Single nucleotide polymorphism (SNP) based copy number profiling represents one modality of testing which is becoming widely available and is being increasingly utilized to profile renal tumors. In this special Seminars issue, we explore the evolution of Collecting Duct & Papillary RCC as diagnostic entities, with a detailed discussion of SNP array-based copy number profiling in contemporary clinical practice.Copyright © 2021 Elsevier Inc. All rights reserved.