Metastatic ALK fusion gene-positive lung adenocarcinoma in the mandible with numb chin syndrome as an initial manifestation

Numb chin syndrome (NCS) refers to abnormal sensations caused by injury of the inferior alveolar nerve. Causes are often metastatic mandibular tumors and the prognosis is usually poor. We report the case of a 76-year-old man with NCS as a first symptom of metastatic anaplastic lymphoma kinase (ALK) fusion gene-positive lung adenocarcinoma. Initially, metastatic adenocarcinoma was identified as the cause of NCS by a biopsy. Additional tumors were detected in the lungs, liver, and multiple bone sites by imaging. Immunohistochemical analysis of a biopsy sample revealed positive results for cytokeratin (CK)7 and thyroid transcription factor 1 and negative results for CK20. This result suggested the mandibular adenocarcinoma was a metastatic lung tumor. The metastatic tumor showed positive results on break apart analysis of the ALK gene in fluorescent in situ hybridization. Denosumab and alectinib were administered and the patient has survived 8 years without evidence of lung cancer progression.