Measurement of circulating free DNA in squamous cell carcinoma of the anus and relation to risk factors and recurrence.

Background: Measuring circulating-free-deoxyribonucleic-acid (cfDNA) has created a new framework for personalized treatment in oncology. The aim of this study was to analyze the relation between cfDNA and risk factors and outcome in squamous cell carcinoma of the anus (SCCA).

Methods: Patients treated with radiotherapy for localized SCCA were included in Aarhus, Denmark from 2016 to 2019. Serum samples from baseline, during and after therapy, were measured for the level of cfDNA in copies per mL by a direct fluorescent assay.

Results: Eighty patients were included. Samples were available at baseline (n = 73) mid-therapy (n = 74), end-therapy (n = 67) and one-year follow-up (1Y) (n = 29). P16-positivity was found in 89% (n = 55). The median level of cfDNA was higher for P16 negative tumors (1.48) compared with the P16 positive tumors (0.90, P = 0.04). Data showed a correlation between baseline cfDNA levels and Gross Tumor Volume (R = 0.13, P < 0.01), and increasing levels with increasing T-stage (T1 = 0.80, T2 = 0.94, T3 = 1.11, T4 = 1.3). Higher cfDNA levels were observed in patients with poor performance status (P < 0.01). The cfDNA level decreased from baseline to mid-therapy (0.92-0.78, P < 0.01) and from baseline to 1Y (0.92-0.71, P < 0.01). Baseline levels for patients with treatment failure (n = 8) were above the 25th percentile (p = 0.05) which translates into difference in disease free survival.

Conclusion: Results indicate an association between baseline cfDNA levels and risk factors in SCCA and a low baseline level correlates to lower risk of treatment failure. Findings contribute with new knowledge of the biological role of cfDNA in SCCA and holds potential knowledge for personalized treatment of SCCA.