Cytomorphology is often insufficient to categorize non-small-cell lung carcinoma on FNA specimens

Objectives To determine the accuracy and reproducibility of differentiating between squamous cell carcinoma (SCC) and adenocarcinoma (ADC) on fine-needle aspiration (FNA) specimens. Methods Fifty cases of NSCLC diagnosed by FNA having either concurrent core biopsies or resection as a diagnostic reference standard were selected. FNA slides were reviewed independently by five blinded observers. Two rounds of review were performed. Cases were initially categorized as SCC, favor SCC, NSCLC (type indeterminate), favor ADC, or ADC; while the indeterminate category was eliminated in the second round of review. Results The interobserver agreement was 0.22 and 0.1 with and without the indeterminate category, respectively. The overall accuracy for differentiating between SCC and ADC of the lung was 65% with the indeterminate category and 66% without. Conclusion Overall, the low interobserver agreement in our study indicates that accurate subclassification between the NSCLCs often cannot be made by cytomorphology alone. Diagn. Cytopathol. 2016;44:73-79.