Normal tissue does not grow continually. In the early stages of any cancer, there may not be much visible effect on the body. Cancer cells can break off from the main tumor and travel through the blood stream to other parts of the body. These cancer cells may then form new tumors, known as metastases. As the cancer grows and spreads, or metastasizes, the person will likely begin to weaken.
Cancer places many demands on the normal functioning of the body.
In the advanced stages, symptoms such as weight loss, weakness, and fatigue are common. At the same time, new cancerous tumors that spread to other parts of the body may cause other organs to fail. If not successfully treated, the cancer will cause the person to die by destroying the functioning of vital body systems. Most cancers occur in people older than 55 years. This may be because cells become more vulnerable to damage after years of use.