Clinical Characteristics of Metachronous Second Primary Head and Neck Cancers Occurring 5 Years or More After Treatment for the First Primary Cancer

ABSTRACT Aim The high incidence of second primary cancers (SPCs) among patients with head and neck squamous cell carcinoma (HNSCC) is well‐recognized. Both recurrence and SPCs are routinely assessed during posttreatment follow‐up. Occasionally, secondary cancers develop long after treatment for the first primary cancer (FPC). However, the details of such cases remain unclear. Therefore, this study was conducted to retrospectively elucidate the clinical characteristics of SPCs occurring long after FPC treatment. Methods We investigated the clinical characteristics of SPCs in the head and neck among 443 patients with HNSCC treated at our department. Results A total of 41 (9.3%) patients had metachronous SPCs occur in the head and neck. Twenty‐eight patients underwent surgery to treat SPC, while all four patients who received chemotherapy had previously undergone surgery and radiotherapy. Seven patients were diagnosed outside the follow‐up, and all occurred more than 5 years after FPC treatment. Fifteen patients (3.4%) had SPCs in the head and neck more than 5 years after FPC treatment. Six (40%) patients presented with advanced‐stage disease, which was a higher proportion than those who developed an SPC within 5 years (30.1%). Following SPC treatment, only six patients remained alive without evidence of recurrence. Conclusion Given the poor prognosis associated with SPC, optimizing follow‐up strategies after FPC treatment is crucial to facilitate early detection and improved outcomes. However, owing to limited medical resources, continuous surveillance solely for early SPC detection remains challenging, highlighting the need for further research into practical and sustainable survivorship care for patients with HNSCC.