This division causes the formation of a mass, called a tumor, in the organs where the cells first started dividing. The cells are called malignant, or cancerous. After a while, the cancerous mass continues to grow up to a point where it begins to spread beyond the organ originally attacked. After this, the cancerous cells spread to the tissue and organs neighboring the initial organ.
If the growth of the tumor and division of the cells is not stopped through treatment or surgical intervention, eventually the mass starts applying pressure against other organs, or can penetrate these organs, forming new tumors on these organs. The growth of the tumor beyond certain limits naturally causes some of the malignant cells to detach themselves from the original tumor. After these cells reach the stream of blood or the lymphatic system, this causes the cancer to evolve into a more hazardous form for the patient.
Since the body uses blood vessels and the blood stream to push blood throughout the entire body, it stands to reason that a malignant cell reaching the blood stream can reach just about any part of the patient’s body. Once the cell reaches a new destination, it sort of takes root and starts the division process all over again, in this new location, forming a secondary tumor.
Another way the cells can travel to another location in the body is by way of the lymphatic system, which also crosses the body. However, lymph passes through some filters called lymph nodes, and sometimes the cancer cells can get stuck in these filters and start their division process from there. This is called lymph node metastasis. When the cells corrupted reach all the way to the bone, or when they manage to reach a bone through the blood stream, this process is called a bone metastasis of the cancer.
The cancer that has entered a metastasis phase is much tougher and presents a much bigger challenge against treatments applied by oncologists. At this point, even surgical intervention, through which the tumor is removed, will not be able to prevent the contamination of another part of the body, because the cancer cells have entered the blood stream and are now much more difficult to locate and destroy.
Cancer of the blood kills as the elements of the blood are not accomplishing their tasks and the body’s immune system might completely lose its properties. However, solid tumors are lethal in much more mechanical ways, namely they can literally choke a certain organ to the point where it is no longer able to function, or they can grow to the point where the organ bursts. So, basically, this is the answer to the question “how does cancer kill?” I say basically because, obviously, cancer works in more complicated ways. But this is the gist of it.