Renal Papillary Neoplasms – Concordance Rate between Diagnosis on Fine-Needle Biopsy (FNB) and Subsequent Resection

Summary: Introduction: A number of renal tumors are ablated at the time of FNB and never proceed to resection precluding confirmation of diagnosis. The classification of renal papillary tumors and our understanding of their molecular pathways is evolving. The morphology of these tumors is variegated, with broad differential diagnosis. Herein, we evaluated the rate of concordance between FNB and resection diagnoses. Materials and Methods: Retrospective search of our pathology archives, September 2017 to December 2023, identified all patients with a renal mass who underwent FNB followed by resection at our institution. Cases with FNB final or differential diagnosis equivalent to or including papillary renal cell carcinoma (PRCC) were reviewed for morphological features, immunostaining (IHC) usage, and molecular analysis (when available), and compared with the diagnosis on resection. Discordant and non-conclusive cases in the FNB diagnosis were re-reviewed. Results: Of 304 renal masses diagnosed on FNB, 34 cases (10 female and 24 male), mean age 64 years (range, 22 – 88 years) met inclusion criteria. Concordance between FNB diagnosis and resection was seen in 24 cases (65%); IHC was utilized in 14 cases (58%). Most frequently used IHC were Ck7 (11, 79%), CA-IX (6, 43%), and CD117 (5, 36%). In 7 cases (29%), FNB diagnosis was non-conclusive for PRCC which was included in the differential diagnosis, and diagnosis on resection showed clear cell renal cell carcinoma (CCRCC) (3), PRCC (2), and translocation RCC (2). In 3 cases, FNB diagnosis was discordant from resection that showed CCRCC (2) and oncocytoma (1). IHC was utilized in 8 of these cases (Table 1). Conclusions: This study demonstrates high rate of concordance between FNB and resection diagnoses for renal papillary neoplasms. IHC was helpful in most concordant cases, with the combination CK7 and CAIX differentiating CCRCC from PRCC. However, a subset of CCRCC expressed CK7 positivity that resulted in diagnostic challenges.