Separating distant recurrences from second primaries in head and neck squamous cell carcinomas – A DAHANCA group analysis on paired tumor samples

Background In head and neck squamous cell carcinomas (HNSCC), there is no clinically available method to separate distant metastases (DMs) from SCC secondary primary tumors. The study aimed to assess the genetic relationship in paired tumor samples. Methods Patients with pairs of solid biopsies from the primary HNSCC and suspected DMs were identified (2007–2017). Targeted next‐generation sequencing of 22 genes was applied, including TP53 , supplemented with human papillomavirus (HPV) genotyping. Results Of 55 pairs obtained, 33 were successfully analyzed. Distant biopsies included lung, liver, and bone. A genetic match was found in 23/33 (70%) patients, primarily with identical TP53 mutations or HPV genotypes. In 10/33 patients (30%), the genetic relationship was absent, all with lung involvement. In patients with no lung involvement, 8/8 had a match. Conclusions One‐third of patients with DMs in HNSCC lack a genetic relationship with the primary tumors. The risk of misclassification is most prominent for patients with lung involvement.