The Morphological and Immunohistochemical Spectrum of Papillary Renal Cell Carcinoma (PRCC): A Study of 132 Type 1, Type 2 and 'Mixed' Tumors
Myriam Chevarie-Davis, Chenbo Wu, Simon Tanguay, Mathieu Latour, Fadi Brimo. McGill University, Montreal, QC, Canada; Université de Montréal, Montreal, QC, Canada
Background: PRCCs are classically divided into type 1 and type 2 tumors, according to the 1997 description by Delahunt, et al. However, many routine cases do not fulfill all the criteria for either type and display cytoplasmic or nuclear features of both types. We herein describe the clinical, morphological and immunohistochemical (IHC) features of a large series of PRCCs in order to better characterize the frequency and nature of those 'mixed' tumors.
Design: 132 consecutive cases of PRCC from 2 institutions were reviewed and classified as either type 1, type 2 or 'mixed'. Using tissue microarrays of 95 cases, IHC evaluation of CK7, EMA, TopoIIa, napsin and AMACR was performed using the H-score (staining intensity X % of positive cells). Areas of different nuclear grades within the 'mixed' cases were represented.
Results: The frequency of type 1, type 2, and 'mixed' PRCC was 25%, 28%, and 47%, respectively, with the detection of the latter being unrelated to the extent of tumor sampling. The two main categories of 'mixed' tumors were: 1) cases with nuclear grade 1-2 but no basophilic cytoplasm (type A), and 2) cases with predominantly type 1 histology admixed with areas showing nuclear grade 3-4 with mostly eosinophilic or foamy cytoplasm (type B). Overall, the pathological stage of 'mixed' cases showed concordance with type 1 tumors. At the IHC level, using the only two markers that showed significant staining differences between type 1 and 2 tumors (CK7, EMA), mixed type 'A' cases were similar to type 1. Although the high-nuclear grade areas of mixed 'B' tumors showed some staining differences from their low-nuclear grade counterpart, their IHC profile was closer to type 1 than type 2 tumors (See table).
|Type 1||Type 2||Mixed 'A'||Mixed 'B'|
|Low grade areas||High grade areas|
|Sections per cm||1.7||1.8||2.1||1.9|
|CK7 (H-score), with 95% CI||213 (165-261)||67 (32-103)||219 (152-286)||256 (226-286)||170 (131-208)|
|EMA (H-score), with 95% CI||225 (180-270)||125 (83-168)||225 (173-278)||224 (182-265)||182 (149-216)|