Cancer of the breast can be detected when it grows large enough to either be felt or seen on a mammogram . Sometimes a tumor isn't found for many years. The tumor may distort the shape of the breast or the texture of the skin as it becomes larger. This is because surrounding tissues become fixed to the tumor. 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.