That's almost always the case but there are rare exceptions. Jimmy Carter was one such. His stage 4 melanoma had spread everywhere .. until he was given an experimental drug known as a 'checkpoint blocker'. The idea is.. the body's immune system is ready to destroy the cancer wherever it is but a 'lock' is holding it back. The drug releases that lock. And sure enough his cancer vanished and he lived to be 100.
I have a family member that survived stage 4 colon cancer 25 yrs ago. The Dr. tried a new chemo therapy on him and it worked.
Judy Perkins was another. She had stage 4 metastatic breast cancer and like Jimmy Carter was months from dying. Until she was given an experimental treatment called ‘Tumor Infiltrating Lymphocytes’. Her immune (T) cells were removed, genetically engineered to target her specific cancer and infused back. Like a miracle her cancer vanished from everywhere in her body. These were rare responders but showed that - in theory at least - stage 4 cancer isn’t necessarily incurable and a death sentence.