Question

What are malignant tumors?

Answer 1

According to the American Brain Tumor Association:
Malignant Tumors
Unlike benign tumors, the cell structure of a malignant brain tumor is significantly different than that of normal brain cells. Malignant tumors tend to grow faster and can be more invasive than benign tumors. Malignant tumors are life threatening. Sometimes malignant brain tumors are referred to as brain cancer, though they do not share all of the characteristics of cancer. Most notably, cancer is characterized by the ability to spread from one organ to another. It is very rare for a primary brain tumor to spread beyond the brain or spine.

Answer 2

Malignant tumors grow by invading nearby cells and spread to other parts of the body through a process called metastasis. Cells break off the tumor, enter the bloodstream or lymphatic system, and spread to another area, infecting additional tissue. This is how a tumor which starts in one part of the body, such as the breast or prostate, can spread to another type of tissue, such as the bones.