Lung cancer patients harbouring driver oncogene alterations are markedly responsive to molecular target agents, such as epidermal growth factor receptor (EGFR), tyrosine kinase inhibitor (TKI), and echinoderm microtubule-associated protein like 4 - anaplastic lymphoma kinase (EML4-ALK)-TKI. We encountered an exceptionally rare case, harbouring both EGFR mutation and EML4-ALK fusion gene, and suffering from severe disseminated intravascular coagulation. In this case report, we present two notable points. First, our patient was successfully treated with a third-generation EGFR-TKI, osimertinib. Second, osimertinib could manage severe conditions, such as disseminated intravascular coagulation. Third-generation EGFR-TKIs may be a viable option for patients harbouring both EGFR mutations and EML4-ALK fusion genes, even in severe conditions.