Fine-needle aspirates of hepatocellular carcinoma that are misclassified as adenocarcinoma: correlating cytologic features and performance in the College of American Pathologists Nongynecologic Cytology Program.

Context: The cytologic features of hepatocellular carcinoma in fine-needle aspirates are well described. While some cases are easily distinguished from adenocarcinoma, poorly differentiated tumors can be difficult to differentiate. We reviewed the cytologic findings for 9 aspirates from cases of hepatocellular carcinoma that were frequently misclassified as adenocarcinoma and compared them with another 10 cases of hepatocellular carcinoma that were rarely misclassified.

Objective: To compare the cytologic features of cases of hepatocellular carcinoma in fine-needle aspirates that were both rarely and frequently misclassified as adenocarcinoma.

Design: We reviewed a total of 762 interpretations from 19 different cases of hepatocellular carcinoma in liver fine-needle aspiration specimens in the College of American Pathologists Nongynecologic Cytology Program and correlated the cytologic features with performance in the program.

Results: Overall, cases that were frequently misclassified as adenocarcinoma were misclassified 39% of the time (range, 18%-70%), while cases that were rarely misclassified were classified as adenocarcinoma 2% of the time (range, 0%-8%). The difference was statistically significant (P < .001). On review, 4 cytologic patterns were found. The most common pattern for cases that were rarely misclassified was prominent trabeculae of cells and endothelial cells wrapping the trabeculae (6/10 cases vs 2/9 cases that were frequently misclassified). The most common pattern among cases that were frequently misclassified was clusters of cells with granular cytoplasm and associated stripped nuclei (5/9 cases vs 2/10 cases that were rarely misclassified). However, the distribution of neither pattern was significantly different (P = .16 for both). One case with large atypical granular cells, as seen in the fibrolamellar variant, was rarely misclassified. The remaining 3 cases (2 frequently misclassified, 1 rarely misclassified) had a nonspecific a pattern of cells with granular cytoplasm without obvious trabeculae or stripped nuclei.

Conclusion: Correctly classifying hepatocellular carcinoma by cytology alone remains a significant challenge. While some patterns are more common in cases that performed well and other patterns are more common in cases that performed poorly, there was no significant difference in the distribution of these patterns. These results suggest that people should support their interpretations of aspirations with either immunologic evidence, biopsy evidence, or review by an experienced cytopathologist. Continued educational efforts in this area may be of value.