The Clinical Value of Measuring Circulating HPV DNA during Chemo-Radiotherapy in Squamous Cell Carcinoma of the Anus

Simple Summary Anal cancer is treated with high dose chemoradiotherapy; but despite this, a minor patient group experience treatment failure. Anal cancer is strongly related to human papilloma virus (HPV) infection and previous smaller studies have shown that fragments of HPV DNA can be detected in blood samples from anal cancer patients. This study measured HPV DNA in 88 patients including both small- and more advanced tumors and detected six different subtypes of HPV. During treatment with chemoradiotherapy, the level of HPV DNA decreased, and three elimination patterns with clinical relevance were identified. Fast elimination correlated to a low risk of failure, slow elimination correlated to risk of failure in the pelvis, and persistent HPV DNA after treatment correlated to a high risk of later distant failure. The results add new information to the increasing interest in research of HPV DNA in HPV related cancers and holds great clinical potential. Background and purpose: Circulating tumor DNA (ctDNA) is investigated in various cancers. In squamous cell carcinoma of the anus (SCCA) infection with human papilloma virus (HPV) is found in around 90% of cases and here, plasma HPV (pHPV) can be used as ctDNA. Preliminary data have proved the ability to detect pHPV16 and -18 in SCCA. We have developed a highly sensitive method for measurement of six relevant pHPV subtypes, to investigate the elimination pattern of pHPV during chemo-radiotherapy (CRT) for SCCA and its clinical value. Material and methods: Patients treated at Aarhus University Hospital from 2016-2020 were included. P16 status in the primary biopsy was measured and 82% of patients had P16 positive tumor. Blood samples were collected prior to treatment (PT), mid treatment (MT), end of therapy (EOT), and during follow-up (FU). An in-house multiplex digital droplet PCR method measured pHPV subtypes 16, 18, 31, 33, 51, 58. Results: Samples from 88 patients were drawn PT (n = 73), MT (n = 72), EOT (n = 64) and during FU (n = 41). Plasma HPV was detectable in 52 patients and PT pHPV levels correlated to tumor stages. Three elimination patterns were observed during CRT with correlation to outcome: fast responders with no local or distant failures (0/12); slow responders with high risk of local failures (4/20), no distant failures; persistent molecular responders with high risk of distant failures (4/13), but no local failures, p < 0.01. Conclusion: During CRT, pHPV can divide patients with SCCA into three groups with significantly different risk of failure. The use of pHPV can potentially assist in clinical treatment decision.