9 out of 10 women are the first to notice a lump or mass in their breast. It usually isn't painful, but can cause an unusual sensation in the area where the lump is. When a tumour grows in the milk ducts, bleeding can occur from the nipple. The size or shape of the breast may change. As well, the nipple might draw in, or some of the skin will pull in causing what looks like a dimple to appear. While these might be early signs of breast cancer, they might also indicate another noncancerous disease. In fact, about 8 out of 10 breast growths are noncancerous. However, a doctor should be consulted to determine the exact cause of the lump.

The most serious complication of breast cancer is metastasis. That's when some cells from a tumour break off and move to other areas of the body - through either the blood or the lymphatic vessels - invading the tissue at new, possibly distant sites. When breast cancer cells metastasize, it's most commonly to the lymph nodes, lungs, liver, bones, brain, and skin. It can take years - even after the breast tumour is diagnosed and treated - before cancer that has spread from the original tumour appears. Once metastatic tumours are discovered, chances are that the cancer has spread to other locations as well, even if they remain undetected.