Emerging role of blood-based biomarker testing in HPV-mediated head and neck squamous cell carcinoma

The incidence of head and neck squamous cell carcinoma (HNSCC) related to human papillomavirus (HPV) has increased dramatically and is expected to continue to rise despite an available prophylactic vaccine.1 HPV-mediated tumors of the head and neck typically arise in the oropharynx (the tonsils or the base of the tongue) and possess distinct clinical and biological characteristics in comparison with non–HPV-related tumors. HPV-mediated HNSCC tends to occur in younger, healthier individuals and is associated with an excellent prognosis.2 As such, clinical trials are now investigating de-escalation approaches with the goal of maintaining excellent survival outcomes while sparing unnecessary treatment and related toxicity. It is now standard of care to perform HPV testing on tissue biopsies from all patients with squamous cell carcinoma arising from the oropharynx or unknown primary sites metastatic to the cervical lymph nodes via p16 immunohistochemistry or other high-risk HPV testing.3 In recent years, it has been demonstrated that HPV circulating tumor DNA (ctDNA) can also be detected in the majority of patients with HPV-mediated HNSCC. HPV ctDNA testing has a sensitivity of 89%–95% and a specificity of 95%–100% in detecting patients with previously untreated HPV-positive oropharynx cancer, which may constitute superior diagnostic performance in comparison with standard tissue sampling.4-7 There is accumulating evidence supporting the use of HPV ctDNA in prognosticating, predicting treatment response, detecting minimal residual disease, and identifying recurrence in HPV-mediated HNSCC.4, 5, 8, 9 Although results from observation cohorts are promising, HPV ctDNA assays have not undergone rigorous validation across institutions or in prospective clinical trials. Therefore, HPV ctDNA testing is not yet recommended in consensus guidelines. High-quality data are urgently needed to determine whether the implementation of HPV ctDNA testing at the time of diagnosis or during surveillance will translate into improved oncologic outcomes and quality of life and whether this will be a cost-effective approach. Despite not being included in consensus guidelines, a commercially available HPV ctDNA test now exists, and it is routinely used by providers given numerous studies demonstrating its clinical validity.4, 10, 11 The lack of evidence-based recommendations regarding HPV ctDNA testing introduces several clinical uncertainties. Can pretreatment HPV ctDNA levels be used to risk-stratify patients? How should a patient be managed if HPV ctDNA does not completely clear after treatment? Do the dynamics of HPV ctDNA clearance during treatment predict the eventual response? What should be done in the case of detectable HPV ctDNA without clinically or radiographically evident disease? Studies suggest that the magnitude of the pretreatment HPV ctDNA level is associated with the overall disease burden4, 12; this is similar to the finding that Epstein–Barr virus plasma DNA levels correlate strongly with stage in patients with nasopharynx cancer.13 However, in HPV-related disease, there are likely multiple factors at play. Some studies suggest that ctDNA levels correlate more strongly with the nodal disease burden than the primary tumor size, whereas others have demonstrated that the tumor HPV integration status and copy number likely influence ctDNA shedding and plasma levels.4, 5 Higher pretreatment HPV ctDNA levels may be associated with a higher disease burden and a worse prognosis5 or episomal viral genomes and an improved prognosis.4 These early studies sequenced few patients, so additional studies comparing the concordance between the tumor HPV integration status and the plasma ctDNA count are needed. In patients treated with upfront surgery, data from small observational studies suggest that the presence of HPV ctDNA just 24 h after surgery is highly suggestive of minimal residual disease.14, 15 However, recurrences also occur in the absence of detectable HPV ctDNA, and this suggests that current assays are not sensitive enough to direct adjuvant therapy. To determine the reliability of HPV ctDNA assays in detecting minimal residual disease, it is critically important to understand test performance characteristics and reproducibility. Variability in test performance is likely related to the DNA detection method, tumor biology, and patient factors affecting clearance.7 Therefore, although postsurgical HPV ctDNA positivity may identify patients who require further treatment, prospective studies are needed to elucidate whether treatment can be adapted on the basis of ctDNA alone or histopathologic analyses will be needed for confirmation. In patients treated with chemoradiation for HPV-mediated HNSCC, data suggest that early dynamic changes may predict the eventual response. One study revealed that an early increase or shedding of HPV ctDNA at Week 2 of treatment predicted disease control,5 whereas another study demonstrated that >95% clearance of HPV ctDNA by Week 4 of treatment was highly associated with disease control.4 HPV ctDNA kinetics likely predict the treatment response to chemoradiation; however, further studies are needed to investigate patient and tissue factors, such as hypoxia and heterogeneity, which likely affect ctDNA shedding and clearance, before treatment is de-escalated on the basis of these patterns alone. Currently, there are no recommendations as to the timing of ctDNA testing after surgery or during chemoradiotherapy. On the basis of the available data, it appears as if clinically useful information can be ascertained 24 h after surgery and every 2 weeks during chemoradiation.5, 15 Although HPV-mediated HNSCC is associated with improved treatment responses and overall survival, patients may experience different failure patterns, including late recurrences and dissemination to rarer organs.16 Data support the idea that biochemical recurrence by ctDNA testing occurs months before clinical or radiographic recurrence and highlights individuals who may benefit from early therapeutic intervention.17 However, a positive test does not localize the disease recurrence. Therefore, rising HPV ctDNA levels during posttreatment surveillance should prompt imaging studies and cytopathologic analysis. The absence of clinical or radiographic disease at the time of biochemical recurrence represents a clinical conundrum. The benefits of systemic treatment versus active surveillance in this situation will need to be studied in clinical trials. Contemporary surveillance guidelines do not provide recommendations on the timing of ctDNA testing during posttreatment surveillance. However, existing data suggest that it would be prudent to collect blood samples at each surveillance visit. In summary, it is truly an exciting time in the field of blood-based biomarker testing. For patients with HPV-mediated HNSCC, HPV ctDNA analyses are likely to change clinical practice. The kinetics of ctDNA clearance during treatment as well as the presence of posttreatment ctDNA will likely be used to adapt treatment, and clinical trials are currently underway to test these hypotheses. To incorporate HPV ctDNA testing into consensus guidelines, rigorous validation and well-designed prospective trials to prove clinical utility are urgently needed. The authors declare no conflicts of interest. Catherine T. Haring, MD, is an assistant professor in the Department of Otolaryngology–Head and Neck Surgery at The Ohio State University in Columbus, Ohio. Dr Haring completed her residency training at the University of Michigan and advanced fellowship training in head and neck surgical oncology and microvascular reconstruction at The Ohio State University. She helped to develop a plasma-based assay to detect circulating tumor DNA in patients with human papillomavirus–mediated head and neck cancer. As a surgeon–scientist, Dr Haring seeks to study how we can use biomarker tests to detect occult disease, predict treatment outcomes, and ultimately develop precision oncology–based treatment strategies. James W. Rocco, MD, PhD, received his MD and PhD degrees from the Mount Sinai School of Medicine in New York City. He completed his otolaryngology–head and neck surgery residency and postdoctoral fellowship at the Johns Hopkins Hospital. His research interests include biomarkers of treatment response in head and neck squamous cell carcinoma (HNSCC) with a focus on genetic intratumor heterogeneity, tumor genetic progression modeling, and the prognostic role of the estrogen receptor in human papillomavirus–related HNSCC. He currently serves as professor and chair of the Department of Otolaryngology–Head and Neck Surgery at The Ohio State University in Columbus, Ohio.