Distant metastases in squamous cell carcinoma of the pharynx and larynx: a population-based DAHANCA study

Background: In head and neck cancer, distant metastases may be present at diagnosis (M1) or occur after treatment (DM). It is unknown whether M1 and DM follow the same clinical development and share prognosis, as population-based studies regarding outcomes are scarce. Therefore, we investigated the incidence, location of metastases and overall survival of patients with M1 and DM. Materials and methods: Patients diagnosed with squamous cell carcinoma of the pharynx and larynx in Denmark 2008–2017 were identified in the Danish Head and Neck Cancer Group (DAHANCA) database. We identified 7300 patients, of whom 197 (3%) had M1 and 498 (8%) developed DM during follow-up. Results: The 5-year cumulative incidence of DM was 8%. 1- and 2-year overall survival for DM (27% and 13%) vs. M1 (28% and 9%) were equally poor. There was no significant difference in location of metastases for M1 and DM and the most frequently involved organs were lungs, bone, lymph nodes and liver, in descending order. In oropharyngeal squamous cell carcinomas, the location of metastases did not differ by p16-status. For p16-positive patients, 21% of DM occurred later than three years of follow-up compared to 7% of p16-negative patients. Conclusion: Incidence, location of metastases and prognosis of primary metastatic (M1) or post-treatment metastatic (DM) disease in pharyngeal and laryngeal squamous cell carcinoma are similar in this register-based study.