Your father is having stage IV carcinoma with metastasis and current treatment would be paliative . The prognosis is poor and these treatments are aimed to increase the survival rate
of your father . Chemotherapy
definitely has their own side effect but at this stage we don' have other options . So have faith on your doctor and get his rest of the treatment peacefully ( rather shifting to different treatment option without completing one).
Hope this ll help
Thanks n regards