Breast cancer is the most common cancer in women in the United States with an incidence that increases about 0.5% per year. In 2008, 178,480 new cases of invasive breast cancer and 62,030 cases of ductal carcinoma in situ (DCIS) were diagnosed with approximately 40,460 female and 470 male deaths. Fortunately, new improvements in screening, diagnosis and treatment have lead to declining mortality rates. Screening mammography programs have increased the detection of DCIS and Stage I with a decreased incidence of Stage II-IV. Currently 96% of breast cancers are detected early and able to be treated successfully. Newly diagnosed cancers are now usually smaller and more often with axillary lymph nodes free of metastases, therefore more amenable to breast conservation and less likely to require chemotherapy. The 5 year survival for Stage I breast cancer is 95% versus only 20% for Stage IV. In addition, the cost of treating early breast cancer is ten times less than that of late Stages.
It has been shown that breast cancer is a heterogeneous systemic disease associated with different clinical outcomes. Pathologic assessment of the status of both hormonal (estrogen and progesterone receptors) and human epidermal growth receptors (HER2) contributes to staging, prognosis and therapy choices. We know that the most successful therapeutic chemotherapy regimens are those that target these receptors. Since metastatic breast disease is seen in 25-40% of patients and is incurable, it is important to identify the extent of the disease so that the appropriate therapy is started.
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