Background: Induction chemotherapy (IC) is being studied as a chemoradiation (CRT) de-intensification strategy in HPV-related head and neck cancer (HNC), but using imaging response for eligibility selection is distinctly limited by delayed correlation with biological response and difficulty in distinguishing active tumor from treatment effect. We report serial cell free HPV DNA (cfHPV DNA) dynamics as a quantitative measure of early treatment responsiveness for HPV-related HNC patients receiving IC followed by CRT. Methods: Patients with high-risk HPV-positive (by in situ hybridization), locally advanced HNC who received IC followed by definitive CRT were enrolled starting on Sept 26, 2021. Patients received 1-2 cycles of platinum/taxane IC prior to initiating standard-dose CRT. Peripheral blood cfHPV DNA levels were measured biweekly during IC and weekly during CRT with the SafeSEQ HPV test from Sysmex Inostics, an NGS-based, CLIA-certified assay designed to sensitively detect and quantify HPV16 and HPV18 DNA in plasma. Tumor volumes were assessed on the pre- and post-IC planning CT scans by the treating radiation oncologist. Results: To date, 72 plasma samples have been processed across 11 enrolled patients with median age 66 years (range: 35-79). The primary disease sites included 7 oropharynx (OPX), 1 sinonasal, 2 nasopharyngeal, and 1 larynx. All patients had at least cT3 disease or cN3 disease (AJCC 8), with 6 patients having cT4 disease. Five (45.5%) have a smoking history, each > 10 pack-years. We report cfHPV DNA and tumor volume measurements at key timepoints for the 8 patients who have completed IC below. Conclusions: Serial cfHPV DNA identifies a group of locally advanced HPV-related HNC patients who have complete/near-complete cfDNA clearance during IC. This may provide an earlier readout of individualized treatment responsiveness compared to radiologic assessment, and may therefore be a preferred metric for CRT de-intensification eligibility. Clearance velocity will be evaluated with our granular biweekly IC and weekly CRT cfHPV DNA dataset to help further elucidate tumor response kinetics with this paradigm.