Benign tumors are noncancerous masses of cells that can be removed and will not lead to further harm. Malignant tumors refer to tumors that are composed of cancer cells. Malignant tumors have the ability to spread to other tissues, known as metastasis. For example, when cancer is found in breast and have invaded surrounding tissues such as bone.  What separates benign from malignant tumors is the ability of the cells to spread outside of their structure.