Metastatic breast cancer (also called stage IV) is breast cancer that has spread to another part of the body, most commonly the liver, brain, bones, or lungs.

Cancer cells can break away from the original tumor in the breast and travel to other parts of the body through the bloodstream or the lymphatic system, which is a large network of nodes and vessels that works to remove bacteria, viruses, and cellular waste products.

Most breast cancers are detected during routine mammography screening, which is recommended every two years in women aged 50–74 years. Alternatively, women may present with a self-palpated breast lump. Mammographic abnormalities and breast masses require further radiographic evaluation, and, if there are signs of malignancy or the results are inconclusive, histopathologic analysis (biopsy). The axillary lymph node status is determined through clinical examination and biopsy of a suspicious lymph node or sentinel lymph node.

For most sporadic breast cancer, age and female sex are the two key risk factors with most women diagnosed after menopause (median age 59). Family history especially in first or second-degree relatives is also important.

Oestrogen exposure has a role in the genesis of breast cancer, with early menarche, late menopause, and nulliparity being risk factors, and parity, history of breast feeding being protective. Although the risk of breast cancer whilst on the oral contraceptive pill is higher, the overall risk during one’s lifetime is small due to the young age at which women are on the pill. Hormone replacement therapy can increase the risk of breast cancer.

Other lifestyle related risk factors increase high caloric intake during childhood and adolescence, obesity and alcohol.

Some breast pathologies increase the risk of breast cancer such as ductal carcinoma in situ (DCIS), lobular carcinoma in situ and atypical ductal hyperplasia.

Breast cancer is the most common malignancy in women. The most important risk factors include increased estrogen exposure, advanced age, and genetic predisposition (BRCA1/BRCA2 mutations). Most breast cancers are adenocarcinomas. Histopathologic classification differentiates between ductal and lobular carcinomas. The two most common types of breast cancer are invasive ductal carcinoma, which accounts for 70–80% of all cases, and the less aggressive invasive lobular carcinoma. Both types typically develop from noninvasive carcinomas, i.e., ductal carcinoma in situ (DCIS), and lobular carcinoma in situ (LCIS), respectively.

Although masses may be clinically suspicious, radiological diagnosis is obtained with mammogram and ultrasound and a core biopsy provides the definitive diagnosis. Although a fine needle aspiration may show a cancer, histopathology is preferred to differentiate between DCIS and invasive cancer and thus plan appropriate surgical management. Ultrasonography of the axillary lymph nodes is also standard and abnormal lymph nodes are assessed pre-operatively with a fine needle aspiration.

Pre-operative staging with CT chest, abdomen and pelvis and a bone scan are not indicated unless a neo-adjuvant approach is considered or there is a suspicion of metastatic disease. Tumor markers such as Ca 15.3 are not sensitive for breast cancer.

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