Papillary renal cell carcinomas (pRCC) are classically divided into type 1 and 2 tumors. However, many cases do not fulfill all the criteria for either type. We describe the clinical, morphologic, and immunohistochemical (IHC) features of 132 pRCCs to better characterize the frequency and nature of tumors with overlapping features. Cases were reviewed and classified; IHC evaluation of CK7, EMA, TopoIIα, napsin A, and AMACR was performed on 95 cases. The frequencies of type 1, type 2, and “overlapping” pRCC were 25%, 28%, and 47%, respectively. The 2 categories of “overlapping” tumors were: (1) cases with bland cuboidal cells but no basophilic cytoplasm (type A); and (2) cases with predominantly type 1 histology admixed with areas showing prominent nucleoli (type B). The pathologic stage of “overlapping” cases showed concordance with type 1 tumors. Using the 2 discriminatory markers (CK7, EMA), “type A” cases were similar to type 1. Although the high–nuclear grade areas of “type B” tumors showed some staining differences from their low–nuclear grade counterpart, their IHC profile was closer to type 1. Single nucleotide polymorphism array results, although preliminary and restricted to only 9 cases (3 with overlapping features), also seemed to confirm those findings. In conclusion, we demonstrate that variations in cytoplasmic quality and/or presence of high-grade nuclei in tumors otherwise displaying features of type 1 pRCCs are similar in stage and IHC profile those with classic type 1 histology, suggesting that their spectrum might be wider than originally described.
Departments of *Pathology
§Urology, McGill University
‡McGill University and Genome Quebec Innovation Centre
∥Pathologie et Biologie Cellulaire, Université de Montréal, QC, Canada
Conflicts of Interest and Source of Funding: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article.
Correspondence: Fadi Brimo, MD, Department of Pathology, Montreal General Hospital, 1650 Cedar Avenue, Montreal, QC, Canada H3G 1A4 (e-mail: firstname.lastname@example.org).