Abstract
A 50-year-old woman who had previously undergone right hemicolectomy and chemotherapy for colorectal cancer was hospitalized with respiratory failure. Chest computed tomography showed reticulonodular opacities and enlarged lymph nodes. A transbronchial biopsy revealed adenocarcinoma with epidermal growth factor receptor (EGFR) mutations T790M and L861Q. Treatment with the EGFR-tyrosine kinase inhibitor (TKI) osimertinib was started, and she achieved a partial response. We diagnosed her with metastatic lung tumors from colorectal cancer based on additional immunohistochemical staining and the EGFR mutation status (L861Q) of the specimens. Although cases with EGFR mutations have been rarely reported, an EGFR-TKI can be an effective treatment option for colorectal cancer.