"Will modern medicine find way to successfully treat all types of cancer even if the disease has advanced stage and metastases?"

Brief Quora discussion. This sounds really encouraging:

My stage 4 colon cancer is currently in remission after two years of immunotherapy treatment with Opdivo. Instead of killing tumor (and healthy) cells with poison, as chemotherapy does, immunotherapy drugs teach the patient’s immune system to identify tumor cells and destroy them. My cancer had metastasized into my liver and other organs, but my most recent PET scan showed no evidence of disease.