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Breast cancer is a significant cause of morbidity and mortality among women. In the United States, it is the most common malignancy among women. It is estimated that approximately 231,840 new cases of invasive breast cancer will have occurred in the United States in 2015 (1,2). Although lung cancer has surpassed breast cancer as the leading cause of cancer death among women, nearly 39,620 deaths were estimated to occur from breast cancer alone in 2013 (1).
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Since the 1970s, advances in combined-modality therapies have substantially improved the outcomes of patients with breast cancer. Still, approximately 10% to 60% of patients with initial localized breast cancer will suffer a systemic relapse. Metastatic disease is diagnosed at the time of presentation in 3% to 12% of patients depending on the series (1,3). Bone is the most common site of first distant relapse; other common sites of metastases include lymph nodes, lung, liver, and, less frequently, brain. The 5-year survival rate for localized breast cancer is 99%; for metastatic disease, this rate is only 17% to 28% (1,2,3). As is true with cancers in general, the clinical course for patients with metastatic breast cancer (MBC) varies, but as a group, patients with MBC have a median survival of 2 years (4). Patients with bone-only disease tend to live longer than patients with visceral involvement. Untreated patients with MBC have a median overall survival time of 9 to 12 months. With systemic therapy, the mean survival time is 21 months for patients with visceral disease and as long as 60 months for patients with bone-only disease. Survival and response to therapy are affected by several factors, including estrogen receptor (ER), progesterone receptor (PR), and HER2/neu receptor status; performance status; site of disease; number of disease sites; and duration of disease-free interval (DFI).
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The therapeutic objectives and approach to patients with advanced breast cancer is distinct from that of patients with early-stage disease. Treatment for MBC is triaged to endocrine therapy, biological therapy, or chemotherapy, depending on the hormonal and HER2/neu receptor status of the tumor, the severity of symptoms, and the site and extent of disease. Generally, breast cancer can be classified as three molecularly and clinically different syndromes: hormone-receptor positive/HER2/neu negative, Her-2/neu positive (hormone-receptor negative or positive) and triple negative breast cancer. They have different clinical courses, prognoses, metastatic patterns, and responsiveness to available therapies. Systemic treatment prolongs survival, provides palliation of symptoms, and enhances quality of life but, in general, is not considered curative. Therefore, a discussion regarding goals of care is imperative between the patient and treating oncologist. Cure in MBC is rare; less than 2% of patients with MBC may remain disease free after anthracycline-containing therapy. The overall survival of patients has improved in the last few decades due to more effective ...