Retrospective study of time dependency of HPV ctDNA detection after chemoradiation as prognostic biomarker in localized anal cancer

While detection of circulating tumor DNA (ctDNA) weeks after surgery is linked to recurrence for other solid tumors, the optimal time point for ctDNA assessment as a prognostic biomarker following chemoradiation (CRT) for anal cancer is undefined. A retrospective study at MD Anderson Cancer Center (Houston, TX) used a novel droplet digital HPF ctDNA PCR assay for HPV ctDNA in patients undergoing CRT for stage I-III HPV-positive anal cancer, at baseline, at the end of CRT, and during surveillance. Detection of HPV ctDNA at the end of CRT was not associated with recurrence-free survival. Detection of HPV ctDNA at ≥ 3 months after CRT was associated with recurrence (80% versus 2%; OR 168; p<0.0001) and inferior recurrence-free survival (median 4.9 months versus not reached; HR 39.3; pxtagstartz0.0001) relative to HPV ctDNA-negative status. The authors conclude that with a novel, highly sensitive assay, detection of HPV ctDNA at least 3 months after CRT was associated with unfavorable survival.