Tumors in the breast tend to grow slowly. By the time a lump is large enough to feel, it may have been growing for as long as 10 years. Some tumors are aggressive and grow much faster.

About 80 percent of breast cancers begin in the milk ducts, about 10 percent begin in the lobules and a few begin in other breast tissues.

Cancerous tumors can be non-invasive and remain in the milk ducts, like DCIS, or they can be invasive, and break out into nearby breast tissue.

If breast cancer spreads, the lymph nodes in the underarm are the first place it’s likely to go. Metastatic breast cancer (also called stage IV or advanced breast cancer) is invasive breast cancer that has spread beyond the breast and nearby lymph nodes to other parts of the body. The most common sites of metastasis are the lungs, bones, liver and brain.