A Case of Successful Treatment with an Immune Checkpoint Inhibitor after Head and Neck Photoimmunotherapy.

Introduction: Head and neck photoimmunotherapy (HN-PIT) has been conditionally approved by the Japanese government for the treatment of unresectable locally advanced or locally recurrent head and neck cancer since January 2021. HN-PIT makes local treatment of locally recurrent disease possible in cases where systemic drug therapy would have previously been the only option. However, when treatment is ineffective and the disease progresses, it is necessary to shift to conventional drug therapies. We report a case in which an immune checkpoint inhibitor (ICI) was successfully administered to a patient with advanced disease following HN-PIT. Case Presentation: A 75-year-old male patient presented with local recurrence of mandibular gingival cancer. The primary treatment consisted of mandibular segmentectomy and reconstruction with a scapulohumeral and vastus lateralis skin valve. Post-operative radiotherapy was administered. Local recurrence was found in the mid-pharynx adjacent to the reconstruction. HN-PIT was performed for the local recurrence. After three cycles of HN-PIT, the local lesion increased, and the disease was evaluated as advanced. Therefore, the patient was switched to pembrolizumab, an ICI. Conclusion: The recurrent lesions disappeared 2 months after the first dose of pembrolizumab, and the patient remained in clinical remission at 1 year. To the best of our knowledge, there are no other reports of successful ICI therapy after HN-PIT.