From the Education Committees | Circulating Tumor DNA: HPV-Related Oropharyngeal Cancer Diagnosis, Prognostication, Treatment De-intensification, and Surveillance
The current standard of care dictates that oropharyngeal squamous cell carcinoma (OPSCC) diagnosis entails tissue biopsy and human papillomavirus (HPV) or p16 testing.
Neil Gildener-Leapman, MD, and Wojciech K. Mydlarz, MD
members of the Head and Neck Surgery Education Committee
The current standard of care dictates that oropharyngeal squamous cell carcinoma (OPSCC) diagnosis entails tissue biopsy and human papillomavirus (HPV) or p16 testing. Despite the better overall treatment response and survivorship of HPV-positive patients, some still recur and develop progressive disease. This makes stratification and de-intensification of treatment challenging. There have been a number of studies that have examined ways to de-intensify therapy for patients with HPV-positive oropharyngeal cancer with results indicating that not all patients may benefit from a less intense therapeutic approach.
Surveillance evaluation typically entails careful focus-based interview, physical exam, high definition endoscopy, and imaging. Use of a sensitive molecular screening and surveillance test can become a valuable tool for clinicians and patients. Liquid biopsy testing is a simple and minimally invasive option for blood sampling to look for circulating tumor DNA (ctDNA). Frequently used in Epstein-Barr virus (EBV)-positive nasopharyngeal cancers, ctDNA can be an adjunct to diagnostic biopsies and, more importantly, helpful for confirming tumor treatment response and disease control during surveillance.1
There is now commercially available peripheral blood ctDNA testing for HPV-related OPSCC. This approach was characterized in a 2019 study by Chera, et al. that examined the kinetics of HPV related DNA fragments in the peripheral blood of patients treated with chemoradiation.2 The assay was highly accurate in determining newly identified HPV-related OPSCC. Ability to accurately diagnose patients with HPV related cancer with a blood test, could have implications for patients who have insufficient biopsy material for P16/HPV staining. The study went further and identified a good prognostic phenotype, with high baseline ct HPV16DNA (>200 copies/mL) and a greater than 95% clearance of the ctDNA at one month into chemoradiation. HPV can appear in two configurations in the tumor cell: as either episomal (free viral DNA) or integrated into the cell DNA. Patients with integrated HPV DNA are known to have a worse prognosis and are also indicated by much lower peripheral blood HPV DNA copies/mL. This may also help explain why some patients may have HPV OPSCC, but test negative for peripheral blood circulating HPV DNA, and further illuminates the better prognosis with higher pre-treatment ctDNA levels.
The ability of peripheral blood HPV ctDNA fragment assays to help risk stratify and potentially de-intensify therapy may eventually be elucidated by clinical trials. Baseline HPV copy number concentration could become an inclusion criterion for clinical trials. The ability to measure and quantify peripheral blood HPV DNA may allow for wider de-intensification and observation for patients that receive surgery or radiation therapy only, while also serving to intensify treatment in others with persistently elevated levels. Results from proposed clinical trials may not be available for some time. However, there is already a potential immediate benefit for clinical use in both tumor treatment response and surveillance.
In 2020 Chera, et al. also described the utility of peripheral blood HPV DNA detection in the surveillance of 115 patients treated with curative intent chemoradiotherapy.3 87 patients had undetectable circulating tumor HPV DNA post-treatment with zero recurrences noted after a median follow up of 23 months. For patients with more than one consecutive post-treatment positive result for circulating tumor HPV DNA, 15 out of 16 of those patients recurred, yielding a 94% positive predictive value. Interestingly, some patients had one positive post-treatment blood test and were not found to have recurrence, which raises the question of whether the patient is having immune mediated elimination post-treatment, with continued tumor regression and cure.
Introduction of highly accurate blood-based assays for cancer surveillance could allow for more selective use of resources. Radiographic assessments could be more selective and reserved for persistent ctDNA detection or concerning symptoms. In cases of delayed resolution of disease on post treatment imaging, patient may not need to undergo salvage neck dissection for treated neck disease. Surveillance visits could be more efficient, tailored based on molecular surveillance leading to less frequent clinic visits, and geared more for evaluation of any concerning patient symptoms. In crafting cancer surveillance protocols, the positive and negative emotional effects of repeat testing can be considered. However, there remain many questions that need to be answered prior to widespread adoption including: what is the correct frequency of testing? At Diagnosis and at every subsequent clinic visit? Is there a point where several negative results are sufficient to not undergo further testing? Will HPV ctDNA testing allow for earlier diagnosis of recurrence and/or distant disease? If so, lead-time bias should be considered in assessing salvage outcomes and benefits of earlier detection. Finding the correct balance of these interventions may yield health care cost savings, instead of summative costs of excess investigations during survivorship.
Overall, the preliminary results with the ctDNA assays demonstrate a promising tool for assessing treatment response and surveillance of HPV OPSCC. However, there remain important questions that need to be answered and rigorous testing in clinical trial settings will need to be done prior to utilizing ctDNA results to guide clinical decision making.
- Wu CF, Lin L, Mao YP, et al. Liquid biopsy posttreatment surveillance in endemic nasopharyngeal carcinoma: a cost-effective strategy to integrate circulating cell-free Epstein-Barr virus DNA. BMC Med. 2021 Aug 26;19(1):193.
- Chera BS, Kumar S, Beaty BT, et al. Rapid clearance profile of plasma circulating tumor HPV type 16 DNA during chemoradiotherapy correlates with disease control in HPV-associated oropharyngeal cancer. Clin Cancer Res. 2019 Aug 1;25(15):4682-4690. doi: 10.1158/1078-0432.CCR-19-0211
- Chera BS, Kumar S, Shen C, et al. Plasma Circulating Tumor HPV DNA for the Surveillance of Cancer Recurrence in HPV-Associated Oropharyngeal Cancer. J Clin Oncol. 2020 Apr 1;38(10):1050-1058. doi: 10.1200/JCO.19.02444. Erratum in: J Clin Oncol. 2020 Oct 20;38(30):3579.