A rare case of Exon 19 deletion transforming to Exon 20 insertion in a case of adenocarcinoma of lung

Abstract

Epidermal growth factor receptor (EGFR) gene mutations play an important role in the presentation, prognosis, and management of non-small cell lung cancer (NSCLC) patients. Several clinical studies claimed the incidence of EGFR Exon 20 insertion mutations in NSCLC and have similar clinical characteristics to those with common EGFR mutations but poorer prognosis. Insertion mutations within the Exon 20 of the EGFR gene are typically located after the C-helix of the tyrosine kinase to result in the domain of EGFR and have been reported to increase the kinase activity of the protein. This eventually leads to the ligand-independent activation of several downstream pathways such as mitogen activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (Pi3K)-(mTOR) mammalian target of rapamycin pathways, which are involved in several cellular processes such as cell proliferation, metastasis, and migration while preventing apoptosis. Thus, EGFR exon insertion mutations are gain of function mutations. Specific EGFR and frame-in insertions occur in 3–7% of NSCLC and are known to predict primary resistance to treatment with all clinically available EGFR-tyrosine kinase inhibitors (TKIs). Many clinical and preclinical studies have reported significant antitumor activity with various first and second-generation EGFR TKIs such as Erlotinib, Gefitinib, and Afatinib and have led to prolonged survival in EGFR mutated patients, as compared to wild-type EGFR tumors with chemotherapy. In addition, third-generation EGFR TKIs, such as Osimertinib, have shown encouraging results in metastatic NSCLC patients harboring EGFR mutations including EGFR, p. Thr790Met-mutations, that have shown to confer resistance to first and second-generation EGFR TKIs and who have progressed on prior TKI therapy. Drugs such as Afatinib, Dacomitinib, Erlotinib, Gefitinib, and Osimertinib have already gained FDA approval for use in EGFR-mutated metastatic NSCLC patients. Here, we report the case of a 47-year-old man who is a non-smoker with an EGFR Exon 19 positive NSCLC treated with Gefitinib developed an EGFR Exon 20 insertion positive brain metastasis initiated on Afatinib as the targeted therapy and responded well to the treatment.