Practical Application of Circulating Tumor-Related DNA of Human Papillomavirus in Liquid Biopsy to Evaluate the Molecular Response in Patients with Oropharyngeal Cancer

Abstract

Recent findings have shown that human papillomavirus (HPV) DNA is present in the blood as a tumor-specific biomarker (circulating tumor-related HPV; ctHPV) in patients with HPV-related oropharyngeal cancer (HPV-related OPC). The molecular response (MR) in patients with HPV-related OPC can be defined as the change in the number of ctHPV copies in relation to its initial quantity. The optimal model for assessing the MR using a liquid biopsy (LB) should be based on the E6/E7 sequences of the viral genome. MR assessment can help to evaluate the intensity of ongoing treatments in relation to the tumor response. The evaluation of the residual disease at the end of therapy may also be performed by MR assessment. If a partial MR (pMR) is found, caution is indicated and a subsequent LB should be considered, due to the likelihood of disease progression. Complete radiological and clinical responses together with a complete MR (cMR) convincingly indicate a low risk of treatment failure. Moreover, molecular recurrence (Mrec) during a follow-up, confirmed in two consecutive assays, even despite the lack of any other clinical or radiological symptoms of progression, indicates patients at high risk of disease recurrence. In conclusion, MR by ctHPV assessment may hasten the early detection of disease progression, at any stage of the management of the patient with HPV-related OPC.

Keywords: chemotherapy; circulating tumor HPV DNA; human papillomavirus; liquid biopsy; molecular response; oropharyngeal cancer; radiotherapy.

Figure 1

The identification of HPV-related cancer by liquid biopsy in the primary diagnosis of a patient with oropharyngeal cancer (OPC). (A) In the first line of molecular diagnostics, the use of a fast, simple, and inexpensive ddPCR or qPCR technique enables the detection of the most common HPV16 virus in the LB; (B) a positive HPV16 result indicates an HPV16-related OPC; (C) a negative ddPCR/qPCR result is an indication for in-depth molecular diagnostics, due to the possibility of other HR HPVs; (D) the use of more expensive and complex NGS-based molecular diagnostics gives the best chance of detecting other types, preferentially performed in a LB (or optionally on scraps); (E) a positive HR ctHPV result in NGS indicates an HPV-related OPC; and (F) a negative NGS test result indicates a disease independent of the HPV etiology.