Why does cancer spread or come back once its taken out?

Question

Why does cancer spread or come back once its taken out?

Answer 1

Cancer is caused by cells that multiply to often.  They multiply and multiply until they cause a tumor.  When the tumor is removed the doctors might be able to get all the cells that are dividing to often, but if they don't get them all the tumor will come back.  It can spread by the "bad" cells migrating to other parts of the body or getting in the blood stream.

Answer 2

Cancer usually comes back because it is very hard to "kill off" every cancer cell. This is hard to achieve because chemotherapy and radiation treatment can only kill cells that are in the reproductive phases (they are multiplying), this is when the cells are most vulnerable to destruction. The reason why you can only kill the cells in this phase is because they look exactly and act exactly like our regular cells. The only difference is that they are multiplying out of control. So chemotherapy and radiation try to attack them during these vulnerable stages. HOWEVER, the tricky part is that not all the cancer cells undergo mitosis at the same time. So this means that radiation/chemotherapy treatment needs to be repeated several times in order to catch cells that are AT THAT SPECIFIC TIME UNDERGOING MITOSIS.  It is very difficult to kill them all because some can have such a long reproductive cycle.

Cancer spreads because cancer cells are loosely attached together. This is a common characteristic of cancer cells. Whereareas, regular non-cancerous cells bind tightly together.

Also, when surgery or even a biopsy is performed it increases the risk of spreading the cancer. What can happen is that when the surgeon cuts into the tumor and pulls it out. If that instrument touches any other tissue; cancer cells can fall off the knife. We call this "seeding" This is especially risky when a biopsy is performed. During a biopsy the surgeon injects a needle with a special tip, removes a piece of tissue and pulls it out with the needle. This is often the most common cause of seeding and thus spread.