Tumors

Not all tumors are cancerous, tumors can be benign or malignant.

• Benign tumors aren't cancerous. They can often be removed, and, in most cases, they do not come back. Cells in benign tumors do not spread to other parts of the body.
• Malignant tumors are cancerous. Cells in these tumors can invade nearby tissues and spread to other parts of the body. The spread of cancer from one part of the body to another is called metastasis.

Some cancers do not form tumors.

 For example, leukemia is a cancer of the bone marrow and blood.