Sustained Clinical and Metabolic Response to Pembrolizumab-Based Therapy for Suspected Persistent or Recurrent Oral Tongue Squamous Cell Carcinoma After Salvage Surgery: A Case Report

Recurrent oral tongue squamous cell carcinoma (OTSCC) is associated with poor prognosis despite multimodal treatment, and durable responses to immune checkpoint inhibitors remain uncommon.We report the case of a 73-year-old man with a history of pT1N0 moderately differentiated tongue squamous cell carcinoma treated with surgery and adjuvant radiotherapy in 2014 who developed biopsy-confirmed locoregional recurrence after a 10-year disease-free interval.He underwent salvage right partial glossectomy, right selective neck dissection (levels I-IV), and radial forearm free-flap reconstruction.Postoperative clinical and radiological findings raised concern for suspected persistent or recurrent disease, prompting initiation of palliative systemic therapy with pembrolizumab, paclitaxel, and carboplatin.Following an initial partial response, treatment was subsequently continued with pembrolizumab-based therapy, with the addition of low-dose cyclophosphamide from cycle 8 onward.Serial PET/CT imaging demonstrated progressive disease regression, culminating in sustained absence of clinically evident disease and near-complete radiological response after more than 23 cycles of pembrolizumab-based therapy, with no evidence of locoregional or distant disease progression on follow-up.During treatment, the patient developed hypothyroidism requiring gradual escalation of levothyroxine replacement, which was successfully managed without interruption of immunotherapy.This case highlights the potential for sustained disease control with pembrolizumab-based therapy in selected patients with suspected persistent or recurrent OTSCC, despite palliative treatment intent, while emphasising the importance of vigilant recognition and management of endocrine adverse events during extended immunotherapy.