Impact of Second Primary Cancers on Treatment Modifications in Patients with Newly Diagnosed Head and Neck Cancer Referred for Curative-Intent Radiotherapy: A Retrospective Study

Objective: Development of second primary cancers (SPCs) is a significant risk for head and neck cancer (HNC) patients. This study investigates the impact of synchronous and metachronous SPCs on treatment strategies of newly diagnosed HNC. Methods: We retrospectively analyzed patients referred for curative-intent radiotherapy between 2022 and 2024. The primary outcome was the impact of SPCs on HNC (chemo)radiotherapy strategies, with SPC prevalence and distribution as secondary outcomes. Results: A total of 285 patients were included. In 28.4% an SPC was observed. A total of 8.4% had a synchronous malignancy, 16.5% were treated for another malignancy in the past and 3.5% presented with both a synchronous and metachronous cancer. The treatment was impacted in 37.0% of patients with an SPC. Treatment modifications included altered radiotherapy field (23.5%), treatment delays (13.6%), adjusted radio- or chemotherapy regimens (2.5% each), and transition to palliative care (1.2%). Conclusion: A substantial proportion of SPCs influenced the radiotherapy (RT) management in all domains. The complexity of treatment was further increased by the need for additional pre-treatment evaluations and consideration of prior therapies.