A breast tumor is a growth in breast tissue, and it can be either benign (non-cancerous) or malignant (cancerous). Malignant breast tumors, if left untreated, can spread and become life-threatening. The most common symptom of breast cancer, a type of malignant tumor, is a new lump or thickening in the breast.
Although they may require surgical removal to prevent their interfering with normal breast function, they will not invade surrounding tissue; they are not life threatening. Malignant breast tumors, however, if not detected and treated early, will continue to grow, invading and destroying adjacent normal tissue.