| Popis: |
Background: Most often EGFR mutation analysis is performed on formalin fixed paraffin embedded (FFPE) tissue however, alcohol-fixed cytology smears are a potential diagnostically useful source of DNA. Although the use of cytology specimens for EGFR testing has been investigated, new studies are needed to further investigate the validity of this practice. Method: EGFR mutations were analysed in a cohort of 98 patients with non-small cell lung carcinoma (NSCLC) of adenocarcinoma subtype. Mutation analysis was performed on paired specimens of FFPE tissue and air-dried methanol-fixed cells, predominantly derived from the same tumour in the same patient. FFPE tissue provided the reference status for EGFR mutation. Cytology smears were tested for EGFR mutation, and this result was compared to the FFPE reference mutation as being concordant or non-concordant. Cytology smears are hypothesised to be non-inferior to FFPE tissue for EGFR testing. This hypothesis was assessed using a 95% confidence interval (CI) that required a sample size of 100 cytology specimens. 35 specimens were from 33 EGFR positive patients, and 65 specimens were from 65 EGFR negative patients. Results: 97% (34/35) of cytology specimens tested EGFR positive and correlated with their paired FFPE tissue result. 1 false negative result was observed when the paired FFPE tissue result was positive for point mutation G719X. 1 cytology specimen gave a stronger signal for point mutation T790M, when the paired FFPE tissue result was low level positive. 100% (65/65) correlation was observed between cytology specimens that tested EGFR negative compared to their FFPE tissue counterparts. EGFR mutations were detected on cytology smears as exon 19 deletions (41%), L858R (38%), G719X (9%), L861Q (6%) and exon 20 insertions (3%). 1 patient with an L858R mutation had a co-existing T790M resistance mutation (3%). No S768I point mutations were observed. Conclusion: Air-dried methanol-fixed cytology smears provide a diagnostically useful source of DNA when compared to FFPE tissue. Importantly, tumour cell percentage must be correctly estimated to facilitate accurate molecular genetic testing. For the cytology specimen that failed to identify point mutation G719X, the most likely reason was a low tumour cell percentage with a greater proportion of wild-type DNA. |
