Cancer is a complex group of diseases characterized by the uncontrolled growth and spread of abnormal cells. While not all types of cancer are equally deadly, the potential for a cancerous tumor to metastasize, or spread to other parts of the body, is what makes cancer particularly deadly. When cancer cells invade nearby tissues and travel through the blood or lymphatic system to form new tumors in other organs, the disease becomes more difficult to treat and can be life-threatening. read more >>

But increased cell proliferation alone is not enough to cause cancer. A tumor is considered cancerous only if its cells have the ability to invade surrounding tissue, in which case it is said to be malignant. ... This metastasis is what makes cancer so deadly.read more >>