The objectives of this study were: 1) to determine the diagnostic concordance of non-small cell lung carcinoma (NSCLC) subtypes in cytology and biopsy specimens taken during the same procedure and evaluate the causes of discordance; and 2) to determine the frequency of immunohistochemistry (IHC) use for subtyping NSCLC.
Biopsy and cytology specimens that were obtained at the same procedure and diagnosed as NSCLC between January 2011 and December 2014 at the McGill University Health Center were identified (n = 226 pairs). The diagnostic concordance between the 2 methods was evaluated. The slides from discordant cases were reviewed, and final diagnoses were made based on IHC, resection specimens, or pathologist discussion.
Concordance in subtype diagnosis was perfect (adeno-adeno or squamous-squamous) in 66.2% of cases and was partial (adeno or squamous vs non-small cell) in 23%; discordance (adeno vs squamous) was observed in 7.8%. Although subtyping was not possible (ie, the final diagnosis was NSCLC, not otherwise specified) in 12.8% of biopsy specimens and 16.3% of cytology specimens, specific subtyping was not achieved in only 3% of cases when both modalities were considered. IHC was used in 47% of biopsy cases and 13% of cytology cases.
Subtyping of NSCLC can be achieved in most cases (97%) by considering findings in both biopsy and cytology specimens, and concordance in subtyping between cytology and biopsy specimens can be reached in a high percentage of cases (89.2%). Cancer Cytopathol 2016;124:737-43. © 2016 American Cancer Society.