Malignant cancer is a type of cancer that is considered to be aggressive and likely to spread to other parts of the body. Malignant tumors tend to grow and invade nearby tissue and can sometimes spread to distant parts of the body through the bloodstream or lymphatic system. Malignant cancer cells differ from benign cancer cells in that they tend to grow and spread quickly. They can also invade and damage organs and other parts of the body. Treatment for malignant cancer usually involves surgery, radiation therapy, chemotherapy, or a combination of these treatments.