Subtyping of nonsmall cell lung cancer on cytology specimens: reproducibility of cytopathologic diagnoses on sparse material.

Cytologic examination of fine-needle aspiration (material is increasingly used in diagnosing lung cancer. High interobserver agreement in distinguishing small-cell lung cancer from nonsmall-cell lung cancer (NSCLC) on cytologic material has been demonstrated. Because of new treatment-modalities, subclassification of NSCLC into squamous cell carcinoma (SQC) and non-SQC has clinical impact. Subclassification based on morphology alone may be difficult, but applying immunohistochemistry (IHC) to clot-material has proved helpful. When insufficient material is available to make a clot from the aspirate, cytoscrape (CS) can convert cytologic material into tissue fragments useful for IHC. The purpose of this study was to test the reproducibility of pulmonary malignant diagnoses, in particular distinction between subgroups of NSCLC, based on smeared material and IHC on CS. A consecutive series of May-Grunwald-Giemsa (MGG) stained smears and CS with IHC on material from 79 patients suspected of having lung cancer was included. The material was circulated twice to four pathologists. The diagnoses were categorized in five groups: SQC, adenocarcinoma of the lung, non-SQC, benign lesion and other forms of malignancy, including metastases. Reproducibility was analyzed using Kappa statistics. Interobserver reproducibility of the diagnoses in round 1 was good to very good (kappa 0.57-0.71) and very good in round 2 (0.63-0.80). Reproducibility of subclassification of NSCLC based on MGG stained smear and IHC on CS, was very good among experienced pathologists. With only sparse material available, CS should be used to achieve reproducible diagnoses, including subtyping of NSCLC.