Occasionally, breast cancer presents as metastatic disease, that is, cancer that has spread beyond the original organ. Metastatic breast cancer will cause symptoms that depend on the location of metastasis. More common sites of metastasis include bone, liver, lung, and brain. Unexplained weight loss can occasionally herald an occult breast cancer, as can symptoms of fevers or chills. Bone or joint pains can sometimes be manifestations of metastatic breast cancer, as can jaundice or neurological symptoms. Pleural effusions are not uncommon with metastatic breast cancer. Obviously, these symptoms are "non-specific," meaning they can also be manifestations of many other illnesses.

Epidemiologic risk factors and etiology

Epidemiological risk factors for a disease can provide important clues as to the etiology of a disease. The first work on breast cancer epidemiology was done by Janet Lane-Claypon, who published a comparative study in 1926 of 500 breast cancer cases and 500 control patients of the same background and lifestyle for the British Ministry of Health.

Today, breast cancer , like other forms of cancer, is considered to be the final outcome of multiple environmental and hereditary factors.Lesions to DNA such as genetic mutations. Exposure to estrogen has been experimentally linked to the mutations that cause breast cancer.^[9] Beyond the contribution of estrogen, research has implicated viral oncogenesis and the contribution of ionizing radiation. Failure of immune surveillance, which usually removes malignancies at early phases of their natural history. Abnormal growth factor signaling in the interaction between stromal cells and epithelial cells, for example in the angiogenesis necessary to promote new blood vessel growth near new cancers.Inherited defects in DNA repair genes, such as BRCA1, BRCA2 and p53.