When the cancer spreads to other parts of the body and can no longer be controlled or treated, the cancer has reached the final stage which leads to death. This is known as terminal cancer.

Treatments
A diagnosis of terminal cancer does not mean all treatments will stop. But the goals of the treatments will change from fighting the cancer to keeping the patient as comfortable as possible. The treatment plan will be customized for the patient’s symptoms and may include medications and other techniques to control pain, and help with constipation, nausea, difficulty breathing, and other concerns.

How long?
When people hear that a condition is terminal, a common question is to ask the doctor how long the patient will live. In most cases, this is a very difficult question for the doctor to answer. The most honest answer may be that he doesn’t know.

https://www.empowher.com/cancer/content/what-terminal-cancer