Dosing Study of Radiation Combined With Tislelizumab and Pamiparib in Patients With Previously Treated Head and Neck Cancer

The purpose of this study is to evaluate the safety, tolerability and maximum tolerated dose of tislelizumab in combination with pamiparib plus chemoradiotherapy (chemotherapy and radiation) in individuals with recurrent head and neck cancer, which means that the person\'s cancer has come back after treatment. Participation in the study should last for about 15 months while participants receive tislelizumab and chemoradiotherapy with pamiparib. Afterwards, they will return to the clinic for follow up every 4 months for 2 years, every 6 month for the next 2 years, and then once a year for the rest of their life.