The tumor will grow through the breast to the outer skin if left untreated. Cancer cells can also enter specialized channels in the breast called lymphatics. Cancer cells travel through the lymphatics to the lymph nodes to form tumors. This most commonly occurs in lymph nodes under the armpit or within the chest. This may occur when the tumor has grown large, but it can also happen sooner.
Cancer cells can also spread, or metastasize, to other parts of the body through the bloodstream.
This can occur when the tumor is large or small. These cells can travel to other tissues and form new tumors. Breast cancer is most often spread to the bones, lungs , brain , and liver. However, any tissue can be affected. Early in the disease, the only symptom may be a painless lump in the breast.