Daily, the cells in our bodies divide, grow, and die off. However, sometimes genes in the cells malfunction and can turn healthy cells (Women Hormone Balance Learn More), into cancerous ones. These out of control cells may form a lump or mass. Now, not all lumps or masses are malignant or benign. However, if left untreated, they can pose a health risk. Approximately 85 percent of breast cancers are in the mammary duct, and the smaller percentage is usually in the lobules. These tumors usually grow slowly, but there are cases of rapid growth from aggressive tumors.