EGFR mutation testing using archival-stained smears in non-small cell lung carcinoma

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) have shown benefits regarding progression-free and overall survival in patients whose tumours show EGFR mutations. Most patients' lung cancer is metastatic when detected. Small tissue samples and cytological materials are widely used in diagnosis. The aim of the present study was to compare the EGFR mutation analysis results between cytology, small biopsies and resections.

Archival material for EGFR testing was reviewed. Cell blocks and/or stained smears and tissue blocks were used where appropriate. The tumour cell count and percentage were recorded as well as the DNA content. The influence of TTF-1 immunoreactivity on EGFR testing was also investigated.

The study cohort included 300 unpaired specimens of 84 resections, 83 small biopsies and 133 cytological materials. EGFR mutation rates did not differ significantly for cytology, small biopsy and resections (P > 0.05). The higher tumour cell percentage in FNAs than in exfoliative cytology did not affect the EGFR mutation status. EGFR mutation rates were similar when either slides or cell blocks were used. Cytology slides revealed a higher tumour cell content and DNA concentration than the cell blocks. May-Grünwald-Giemsa (MGG)-stained smears had higher rates of the EGFR mutation than the Papanicolaou (Pap)-stained slides (P < 0.05). Tumours with negative immunoreactivity for TTF-1 are less likely to have an EGFR mutation (P < 0.05).

Cytological materials can be used successfully for mutation analysis in lung cancer.