Breast Cancer The breast is a gland rich in fatty tissue, lymphatic vessels, ducts and lobes. Cancerous cells can arise in virtually any part of the gland. Often they are detected when a lump forms. The vast majority of breast lumps are not cancerous, but a professional examination is essential to make that determination. There are multiple forms of this cancer, and although the exact cause is unknown, research shows that estrogen is likely to play a significant role. This is due to estrogen’s role in promoting the cellular growth of the breast tissues. Genetic factors play a role in about 5-10% of breast cancers. These individuals must eat a diet that will not promote the development of breast cancer.