Benign, the opposite of malignant, is often used to describe a tumor that is non-cancerous and typically does not metastasize.
In Our Own Words
In describing tumors, the term benign means not malignant. Benign tumors are growths that do not spread or take over like cancer does. While benign growths might be harmless, this is not always the case. For instance, benign growths can apply pressure in a tight space, or press in on a nerve, causing pain. Aside from the not malignant meaning, and in other contexts, benign can refer to a condition that generally causes little or no harm.