A case of advanced gingival cancer is described. The cancer invaded into the mandible and skin of the cheek and was associated with cervical lymph node metastases, mediastinal lymph node metastases, and bilateral multiple pulmonary metastases. The patient received neoadjuvant chemoradiotherapy and local immunotherapy, followed by curative surgery for the primary and neck lesions. Histopathological examination of the primary cancer and the upper and middle cervical nodes (n = 7) indicated a diagnosis of squamous cell carcinoma. Sections of the lower cervical nodes (n = 5) revealed well-differentiated thyroid carcinoma, suggesting that the mediastinal and pulmonary lesions were of thyroid origin. After total thyroidectomy and mediastinal dissection followed by treatment with radioiodine, the multiple pulmonary nodules disappeared. There has been no evidence of recurrent tumour for 5 years.