A Study to Test Whether Treatment With BI 770371 in Combination With Pembrolizumab With or Without Cetuximab Helps People With Head and Neck Cancer Compared With Pembrolizumab Alone

This study is open to adults with head and neck cancer. The purpose of this study is to find out whether combining different study medicines makes tumors shrink in people with head and neck cancer. The tested medicines in this study are antibodies that act in different ways against cancer. BI 770371 and pembrolizumab may help the immune system fight cancer. Cetuximab blocks growth signals and may prevent the tumor from growing. Participants are put into 3 groups randomly. Each group receives a different combination of study medicines. All study medicines are given as an infusion into a vein at the study site. Participants can stay in the study as long as they benefit from treatment. Doctors regularly check the size of the tumor and check whether it has spread to other parts of the body. The doctors also regularly check participants\' health and take note of any unwanted effects.