Detection of EGFR mutations in samples with few cancer cells in non-small cell lung cancer (NSCLC) patients (p) and distribution of exon 20 mutations

8073 Background: Detection of EGFR mutations in advanced NSCLC p is very often limited by the small amount of tumor tissue. We developed a protocol to determine EGFR mutations in tumor samples containing less than 150 cancer cells. We also studied the distribution of EGFR mutations throughout tumor samples in p progressing after erlotinib treatment. Methods: Cancer cells were microdissected directly into PCR buffer and amplified by a nested PCR. This preliminary microdissection ensures that only cancer cells are collected. Exon 19 del were subsequently detected by sequencing and Genescan, and exon 20 (T790M) and exon 21 (L858R) mutations by sequencing and TaqMan assay. Results: We examined 268 samples of primary NSCLC having less than 150 cancer cells. EGFR gene status was assessable in 213 samples (79%); 45/45 fresh cytological specimens - pleural effusions, fine-needle aspirates, broncoalveolar lavages, sputum - and 168/223 paraffin-embedded samples. Samples having as little as 8 cancer cells were succe...