how often is cancer responsive to chemo/radiation?

my relative has cancer in his neck, laryngeal cancer i believe because its affecting his voice, breathing and eating. plus he had to have a trach put in. he was told the chemo they were giving him wasnt affecting his cancer very much, so they swithced him to a stronger chemo and he will have a PET scan again in a couple months. i mean from the many deaths cancer causes every year, could it be from catching it too late or from being unresponsive to chemo/radiation?