Cytomorphological correlates of epidermal growth factor receptor mutations in lung carcinoma

The initial diagnosis of lung carcinoma is frequently made by fine-needle aspiration biopsy. Novel therapeutic strategies of this disease include tyrosine kinase inhibitors (TKI), such as gefitinib (Iressa) or erlotinib (Tarceva), which target the kinase domain of epidermal growth factor receptor (EGFR). Somatic mutations of this region have been shown to predict a therapeutic response of lung carcinomas to TKI. EGFR mutations have been described in adenocarcinomas of the lung, especially the bronchioloalveolar subtype, which has both cytopathologic and histopathologic definitions. This study investigates whether tumors with EGFR mutations display a characteristic phenotype on fine-needle aspiration biopsy. We identified 37 fine-needle aspiration biopsy of lung masses on which molecular analysis for EGFR mutations was available. Molecular analysis was performed on DNA isolated from formalin-fixed, paraffin-embedded, or frozen tissue from the corresponding core biopsies/cell blocks or resection specimens followed by PCR with primers for the tyrosine kinase region exons 18-24 and nucleotide sequence analysis by gel electrophoresis. Two observers who were blinded to the mutational data assessed several cytomorphological parameters. A semiquantitative analysis included predominant tissue pattern (flat or overlapping), nuclear features (nucleoli, intranuclear inclusions, grooves), cytoplasmic qualities, and extracellular material. All cases were adenocarcinomas primary in the lung. Thirteen cases showed EGFR mutations in exons 18, 19, 20, or 21 of the tyrosine kinase domain. The 24 cases negative for the relevant mutation served as the control group. Tumors with EGFR mutations were statistically more likely to demonstrate a predominantly flat, monolayer architecture (P=0.04) with nuclear inclusions (P=0.014) and the absence of macronucleoli (P=0.001). The predominance of flat monolayers in conjunction with the absence of extracellular mucin and macronucleoli indicated the presence of EGFR mutations with a positive predictive value of 69% and a negative predictive value of 92%. All four cases with extracellular mucin were negative for the examined mutations. Some of the traditional cytomorphological features of bronchioloalveolar carcinoma, i.e., flat monolayers, intranuclear inclusions, and the absence of macronucleoli, statistically correlated with the presence of mutations within the tyrosine kinase region of EGFR. Cytomorphological features could serve as an adjunctive predictive marker of response to TKIs and possibly to other new therapies in development.