Background: Epidermal growth factor receptor (EGFR) mutation is most commonly oncogenic driver in lung adenocarcinoma with 50% incidence in Asians.Osimertinib is the third-generation epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI), which has been widely used in metastatic EGFR-mutant non-small cell lung cancer (NSCLC) and has significantly improved outcomes. At present, the treatment of HNSCC mainly relies on surgery or chemoradiotherapy. EGFR is overexpressed in more than 90% of head and neck squamous cell carcinoma (HNSCC). Targeted therapy for HNSCC is mainly monoclonal antibodies, while the application of small molecule inhibitors is limited. The EGFR-TKI can only be applied in subsequent-line, when disease progression on or after platinum therapy. However, the efficacy of EGFR-TKI in patients with both NSCLC and HNSCC remains unclear. Methods: We searched all patients with EGFR-mutation metastatic non-small cell lung cancer and HNSCC who used EGFR-TKI in the Second Xiangya Hospital. Tumor sections were assessed immunohistochemically using PD-L1 and EGFR expression. EGFR amplification was detected by fluorescence in situ hybridization (FISH). We collected clinical characteristics and treatment histories for all patients including time to progression on EGFR-TKI. Time to progression on EGFR-TKI was defined as time from start of EGFR-TKI to time of radiographic RECIST progression. The efficacy and prognosis were evaluated based on the RECIST (version 1.1). Results: We found an advanced lung adenocarcinoma patient who harbored an EGFR-mutation and concurrently had tongue squamous cell carcinoma with EGFR wild-type.The tongue tumor tissue sample for EGFR expression was positive by immunohistochemistry and EGFR amplification was negative by FISH. NGS showed inactive mutation of patched1 (PTCH1) and EGFR wild-type.PET-CT scans demonstrated a partial response (PR) of the lung tumor and tongue cancer after two months of treatment of osimertinib. The lung tumor maintian partial response until now (nearly 30 months). And the tongue tumor reached the first progression- free survival (PFS) at 21 months. Conclusions: The patient with NSCLC and tongue cancer who exhibited objective response to EGFR-TKI, osimertinib monotherapy. The result indicates a clear response of tongue cancer to osimertinib and the potential for the use of osimertinib in tongue cancer. However, with the specific mechanism largely unknown, it is necessary to study further the effect of osimertinib on HNSCC.