Lung Adenocarcinoma with Pulmonary Miliary Metastases and Complex Somatic Heterozygous EGFR Mutation

The pretreatment detection of an activating mutation of EGFR is now routinely performed in metastatic nonsquamous non-small cell lung cancer (NSCLC). The therapeutic impact of such a detection is major, as patients with advanced NSCLC exhibiting a mutation of exon 19 or 21 will benefit from EGFR-tyrosine kinase inhibitors (TKI). The presence of an EGFR resistance mutation, such as T790M in EGFR-TKI-naïve patients, is seldom looked for and is related either to a germinal mutation or to somatically mutated subclones. It has a negative predictive impact. We present the case of a patient with a lung papillary adenocarcinoma and miliary intrapulmonary metastases whose tumor displays a somatic complex heterozygous EGFR mutation, combining L858R (exon 21) and a primary resistance mutation T790M (exon 20), both detected by direct sequencing.