P2.09-06 Epidermal Growth Factor Receptor (EGFR) Mutation Spectrum in Pulmonary Adenocarcinomas: Indian Experience

Abstract

Incidence of lung cancer is rising in India, which is the major cause of mortality worldwide. The identification of EGFR mutations and ALK fusions in lung cancer has changed the treatment paradigm. The use of tyrosine kinase inhibitor (TKI) is now well established in clinical practice as it improves treatment outcomes. Molecular testing using tumor tissue is the gold standard for targeted therapies. The aim of the present study is to analyze the exact frequency of EGFR activating, rare and coexisting mutations in pulmonary adenocarcinoma (ADC). A total of 783 ADC (755 biopsies and 28 cytology aspirate smears) cases were studied. The male: female ratio was 1: 0.3 with age ranging from 20 to 78 years. During grossing, two tumor blocks were made, one for immunohistochemistry studies and other for mutation testing. In high- cellularity, low- tumor fraction cases, tumor enrichment was done by manual microdissection. We used more than one aspirate smears/biopsy blocks in cases with low- cellularity, high- tumor fraction. Probe-based real-time PCR (RT-PCR) technique was used to analyze EGFR hotspots mutations (exons 18 to 21). Before proceeding for molecular testing, histo/cytomorphology, tumour content and DNA quality were determined. For checking the quality of DNA, RT-PCR was done using wild type EGFR exon 2 primers. About 99% cases passed through the quality check of DNA and only 1.02% (8/783) cases failed. Overall, 234 patients (29.8%) were positive for EGFR mutations. The distribution of different types of EGFR mutations is shown in the Table 1. The common EGFR mutations were Exon 19 del and Exon 21 L858R which were equally distributed between both the genders. The EGFR mutations were more in non-smokers. T790M was present at baseline in around 3% TKI naive cases and it coexisted mostly with Exon 19 del. Cytological smears also showed EGFR mutations in the same pattern as tissue biopsies and a concordance was seen in cases where matched tissue and cytology smears were available.Table 1EGFR mutation spectrum in pulmonary adenocarcinomasEGFR ExonPercentageSingle Mutations = 89.7% (210/234)EGFR most common mutationsExon 19 del61.5%Exon 21 L858R29.1%EGFR TKI resistant mutation at baselineExon 20 T790M2.8%Rare EGFR Single MutationsExon 18 G719X2.4%Exon 20 S768I1.4%Exon 21 L861Q1.4%Exon 20 Ins1.4%EGFR double mutations = 10.2% (24/234)Common double mutationsExon 19 del: Exon 20 T790M11Exon 19 del: Exon 21 L858R5Rare double mutationsExon 18 G719X: exon 20 S768I2Exon 21 L858R: exon 20 S768I2Exon 20 T790M: Exon 18 G719X1Exon 20 T790M: Exon 20 Ins1Exon 19 del: Exon 21 L861Q1Exon 19 del: Exon 18 G719X1 Open table in a new tab With judicious use and triaging of lung cancer diagnostic specimens, it is possible to perform successful mutation testing in >98% cases. EGFR mutation was positive in about a third of ADC including rare, TKI resistant and coexisting mutations in approximately 10% cases which may have significant therapeutic implications. In patients with limited amounts of tissue, cytology samples can be used for EGFR mutation testing as a promising alternative.