Selective treatment de-intensification with reduced-dose radiation and omitted concurrent chemotherapy guided by response to induction chemotherapy in HPV-associated oropharyngeal squamous cell carcinoma: A single-arm, phase II trial (IChoice-01).

e18069 Background: De-intensification in chemoradiation provides a strategy to optimize the trade-off between treatment efficacy and toxicities in HPV-associated oropharyngeal squamous cell carcinoma (OPSCC). However, the failure of RTOG 1016 and De-ESCALaTE indicated the pitfall of de-escalation in an unselective population and the importance of patient selection for future study design. Induction chemotherapy (IC), as a potential biomarker, has been adopted in several trials to screen candidates for de-intensified treatment based on its tumor response. In present trial, we investigated the feasibility of selectively de-intensified chemoradiotherapy by reducing radiation dose and omitting concurrent chemotherapy guided by response to IC. Methods: From Jan 2019 to July 2020, 48 patients with p16 positive OPSCC, T1-2/N1-3M0 (excluding T1N1M0 patients with single and≤3cm lymph node) or T3-4N0-3M0 according to the UICC/AJCC 8th staging system were enrolled. All of them received two cycles of IC with cisplatin and docetaxel. Those with major response to IC (defined as cCR or ≥50% cPR of both primary site and lymph nodes) received de-intensified treatment with intensity modulated radiation therapy (IMRT) alone with 60Gy to high-risk and 54Gy to low-risk regions (Di cohort). Those with less than major response were given standard chemoradiotherapy with 70Gy to both primary tumor and positive lymph nodes, 63Gy to high-risk and 56Gy to low-risk regions, concurrently with two cycles of cisplatin (St cohort). The primary endpoint was 2-year progression-free survival (PFS). Results: 26/48 (54.2%) patients entered Di cohort while other 22/48 (45.8%) patients entered St cohort. With a median follow-up time of 20.5 months (2.8-36.7months), 3 deaths (1 in Di cohort and 2 in St cohort), 5 loco-regional recurrence (1 in Di cohort and 4 in St cohort) and 6 distant metastases (1 in Di cohort and 5 in St cohort) were documented. The 2-year PFS rates for Di and St cohort were 100% and 60.0% (P = 0.002) with overall survival (OS) rates of 100% and 83.1% (P = 0.062), loco-regional recurrence-free survival (LRFS) rates of 100% and 77.0% (P = 0.035), metastasis-free survival (MFS) rates of 100% and 66.8% (P = 0.011), respectively. Conclusions: For major responders to IC, reduced-dose radiation with omitted concurrent chemotherapy yielded good survival results. In comparison, patients resistant to IC showed poor prognosis even under standard-dose chemoradiotherapy, calling for treatment intensification or development of novel therapeutic agents. Selective de-intensification of chemoradiation guided by response to IC is promising in HPV-associated OPSCC and warrants further evaluation in future studies. Clinical trial information: NCT04012502.