Cyto-histologic agreement in pathologic subtyping of non small cell lung carcinoma: review of 602 fine needle aspirates with follow-up surgical specimens over a nine year period and analysis of factors underlying failure to subtype.

Background: The differential therapeutic efficacy and toxicity of targeted therapies has made subtyping of non-small lung cancer (NSCLC) mandatory. This study aimed to review the accuracy of NSCLC subtyping using lung fine needle aspirates (FNAs) in two periods (before and after the introduction of targeted therapy), checking the reasons for failure and the impact of the use of immunohistochemistry (IHC).

Methods: An electronic search retrieved all NSCLC FNAs with a corresponding surgical specimen from 2001 to 2009. NSCLC, NOS (not otherwise specified) cases from 2005 to 2009 (after targeted therapy) were reviewed to determine reasons for failure in subtyping and to further subtype based solely on cytomorphology. The number of cases in which IHC was performed and the antibodies used were also recorded.

Results: Cytohistological agreement of 602 lung FNAs (341 adenocarcinomas, 93 squamous cell carcinomas and 168 NSCLC, NOS) was achieved in 93.80%. There was a significant decrease in the percentage of cases not subtyped in the period after the introduction of targeted therapy (35.07% versus 24.57%). Final percentage of cases not subtyped after morphological review was 17.03%. IHC was performed in 157 cases, with an increased use in recent years. The number of antibodies did not influence the overall success in subtyping and an average of 3 markers was used. Most frequent antibodies used were TTF-1, CK7, high molecular weight keratin and p63. More than half of cases not subtyped even after IHC corresponded to poorly or undifferentiated neoplasms in the surgical specimens. For the NSCLC, NOS which IHC was not performed, a cell block was produced in 106 cases (75.71%). Review of the cell block slides from 2005 to 2009 showed that the majority (70.7%) had rare, few or no tumor cells.

Conclusions: Specific subtyping can be achieved in a high proportion of lung FNAs with high accuracy. The percentage of NSCLC, NOS has significantly decreased in recent years together with a trend for an increased use of IHC as well as increased number of cell blocks produced. An average of 3 IHC markers was used for subtyping and the number of markers did not influence the overall subtyping.