Background: Among HPV-positive Oropharyngeal Cancer (OPC) patients (pts), some has a less favorable prognosis (T4, N2/N3, smokers >10 pack-year [p/y]). We assume that neoadjuvant immunotherapy might improve their oncological outcomes, so we tested nivolumab (N) prior to ChemoRadiaTion (CRT). Methods: The study population is restricted to HPV positive OPC pts (both p16+ & HPV-DNA+) with advanced disease (T4, N2/N3) or a smoking history >10 p/y. Pts were randomly allocated 1:2 to receive either cisplatin-based CRT (n=20) or 2 cycles of N 240 mg followed by CRT (n=41). The Primary Endpoint (PE) is the rate of pts who can receive Full Treatment in Due Time (FTDT), according to these criteria: a) 2 N infusions on day 1 and on day 14-16 b) CRT started between days 28-37 after the 1st N infusion c) No RT break ≥1 week d) RT dose received >95% of theoretical dose e) Cisplatin dose received ≥200 mg/m² To achieve FTDT, all criteria are required in the Experimental Arm (EA) while only criteria c), d), and e) are required in the Control Arm (CA). In the EA, the trial was designed in 2 steps, with FTDT rate of 88% considered as inacceptable versus an alternative of 98%, a type I error of 0.10, and a type 2 error of 0.08. As per protocol, patient accrual was temporarily suspended after inclusion of 19 pts in the EA (1st step) and results were reviewed by an Independent Data Monitoring Committee (IDMC). To resume pts’ inclusion, FTDT had to be achieved in 18 pts in the EA. Results: From 07/2019 to 09/2020, 30 pts were enrolled including 11 in the CA (demographics are summarized in table). 2 pts in the EA did not reach the PE. For the 1st patient, the cisplatin dose was <200 mg/m² due to grade 1 hearing loss and grade 2 tinnitus (1st cycle: 100 mg/m², 2nd cycle: 80 mg/m², no 3rd cycle). For the 2nd patient, CRT began at D38 due to logistical issues (maintenance of RT devices). As this delay was unrelated to N or to patient's condition, the IDMC considered that the inclusions could resume for the 2nd step. 7 N-related Adverse Events (AE) were reported in 4 pts including 3 serious AE (ankylosing spondylitis flare-up, colitis, diabetic ketoacidosis). Conclusions: Neoadjuvant N before CRT seems feasible for the treatment of OPC pts. The trial has reopened to inclusion as recommended by the IDMC. Clinical trial information: NCT03838263