This clinical trial is focused on studying a type of cancer called squamous cell carcinoma of the head and neck. This cancer affects areas such as the mouth, throat, and voice box. The study is specifically for patients who have had surgery to remove the cancer but are at high risk of the cancer coming back. These patients are not able to receive a common chemotherapy drug called high-dose cisplatin due to various health reasons. The treatment being tested in this study is a medication called xevinapant, also known by its code name Debio 1143. Xevinapant is given as an oral solution, which means it is taken by mouth in liquid form. The study will compare the effects of xevinapant combined with radiotherapy to a placebo combined with radiotherapy.

The purpose of this study is to see if adding xevinapant to radiotherapy can improve the time patients remain free from cancer after treatment, which is known as disease-free survival. Participants in the study will be randomly assigned to one of two groups. One group will receive xevinapant and radiotherapy, while the other group will receive a placebo and radiotherapy. The study is designed to be double-blind, meaning neither the participants nor the researchers will know who is receiving the actual medication and who is receiving the placebo. This helps ensure the results are not biased.

The study will take place over a period of time, with participants receiving treatment and being monitored for any changes in their health. The goal is to determine if xevinapant can help prevent the cancer from returning in patients who are at high risk and cannot receive high-dose cisplatin. This research could provide important information about new treatment options for people with this type of cancer.