Double trouble: Synchronous and metachronous primaries confound ctHPVDNA monitoring

Background: Human papillomavirus-associated head and neck squamous cell carcinoma (HPV + HNSCC) occurs in the oropharynx (HPV + OPSCC), sinonasal cavity (HPV + SNSCC), and nasopharynx (HPV + NPC). Circulating tumor HPV DNA (ctHPVDNA) is an accurate tool for diagnosis, treatment monitoring, and recurrence detection. An emerging challenge with ctHPVDNA is that similar to 7.4% of HPV + HNSCC patients develop synchronous or metachronous HPV+ primaries, which could confound ctHPVDNA monitoring. Methods: We describe a 65-year-old patient with T2N1M0 HPV16 + OPSCC and a 55-year-old patient with T2N2M0 HPV16 + OPSCC. Both patients were enrolled in our prospective observational ctHPVDNA study with longitudinal blood collections throughout treatment. Both patients developed multiple HPV+ primaries. Results: Detailed discussion of the patients' treatment courses, the subsequent diagnoses of their second HPV+ primaries, and their ctHPVDNA monitoring is presented. Conclusions: As ctHPVDNA use becomes more prevalent, it is important to recognize that an increase in ctHPVDNA can come not only from the primary tumor or metastatic clones, but also from synchronous or metachronous second primaries.