The ducts and tubules are the most common sites of breast cancer development, but cancer can also occur in the nipples. Stanford medicine reports that pagets disease accounts for about 4 percent of breast cancer cases 1 2. According to the university of california, san diego, scientists are not sure what causes paget disease. And, as it advances, metastases can occur in distant parts of the body, some of the most common ones being the bones, lungs, liver, and brain. metastasis is when cancer spreads to another part of the body from its original site. Breast cancer most commonly spreads to the bones, liver, lungs, and brain. The most common place for breast cancer to metastasize is into the lymph nodes under the arm or above the collarbone on the same side as the cancer. Other common sites of breast cancer metastasis are the brain, the bones, and the liver. Cancers that have spread only into the lymph nodes under the arm are still curable. Metastatic breast cancer is a general term to describe such situation, and can apply to all types of breast cancer. Common places of the body breast cancer can spread to include the bones, brain, liver, and lungs. This condition can also happen to breast cancer survivors, or those who never had the initial diagnosis of breast cancer. If breast cancer develops in another part of the body it is called a metastatic breast cancer or a metastasis. Where does breast cancer spread to? The most common places that breast cancer spreads to are the bones, liver, lung and brain. Having metastatic breast cancer does not mean that cancer will spread to all these places.