Accuracy of Subclassification and Grading of Renal Tumors on Fine Needle Aspiration Cytology Alone

Acta Cytol. 2021;65(2):140-149. doi: 10.1159/000513065. Epub 2021 Feb 3.


Background: Fine needle aspiration (FNA) of renal masses can distinguish between benign and malignant neoplasms in 73-94% of cases. Previous studies suggested the correct subclassification of renal cell carcinomas (RCCs) by cytomorphology can be achieved in up to 80% of cases. However, as RCCs become increasingly subclassified by molecular signatures, correct subclassification based on cytology alone is increasingly difficult.

Design: Two FNA passes (2 stained with Diff-Quik® and 2 with the Papanicolaou method) were performed on all fresh nephrectomy specimens for a 1-year period. There were 30 cases in this study, with 29 primary renal tumors and 1 case of metastatic lung adenocarcinoma. Each case was assigned a random number and came with 2 slides (1 from each staining method). Eight cytopathologists were asked to provide a diagnosis and the World Health Organization/International Society of Urological Pathology (WHO/ISUP) grading if applicable. Fleiss' Kappa and Cohen's Kappa equations were used to look at inter-rater variability.

Results: When compared to the surgical pathology diagnosis, the average percent correct diagnosis for all cytopathologist was 35%. Chromophobe RCCs had the best average percent accuracy at 72% followed by clearcell RCC at 48%. Average accuracy for grading RCCs was 40%. Inter-rater variability among the cytopathologists for all RCC diagnoses was fair with a Fleiss' Kappa coefficient of 0.28. For the WHO/ISUP grade, the weighted coefficient for each pathologist ranged from 0.11 to 0.45, ranging from fair to moderate, respectively.

Conclusions: Renal tumors are difficult to classify on cytopathology alone. Core needle biopsy and ancillary studies are necessary if diagnosis will change management.

Keywords: Fine needle aspiration; Interpretation of cytological features according to clinical and molecular genetic data; Renal cancer.

MeSH terms

  • Azure Stains
  • Biopsy, Fine-Needle
  • Carcinoma, Renal Cell / classification
  • Carcinoma, Renal Cell / pathology*
  • Carcinoma, Renal Cell / surgery
  • Humans
  • Kidney Neoplasms / classification
  • Kidney Neoplasms / pathology*
  • Kidney Neoplasms / surgery
  • Methylene Blue
  • Neoplasm Grading
  • Observer Variation
  • Papanicolaou Test
  • Predictive Value of Tests
  • Reproducibility of Results
  • Xanthenes


  • Azure Stains
  • Diff Quik
  • Xanthenes
  • Methylene Blue