Breast Cancer Personalized Medicine

W.B.C. is Special Editor of the Breast Cancer Theme Issue. Personalized medicine, individualized medicine, and precision medicine are interchangeable terms that describe an approach to the treatment of disease that harnesses our understanding of the molecular basis and mechanisms of a given disease and matches appropriate therapeutic interventions. Breast cancer represents a diverse collection of malignant diseases of the breast with highly variable clinical behaviors and disparate responses to therapy. The perplexing challenge of patient management for the clinician is reflected in the observation that among breast cancer patients with similar disease (based on traditional histopathological measures) and similar therapeutic strategy, some patients will be cured (and thereafter live a normal lifespan) whereas others will progress to premature death. In fact, we now recognize that breast cancer is tremendously complex in its molecular pathogenesis, natural history, and biology. Breast cancer affects not only women but also men (1% of cases). It occurs both as sporadic malignant disease and as hereditary disease. Hereditary breast cancers manifest in patients with strong genetic predisposition involving BRCA1 and BRCA2 genes, as well as in patients with familial cancer syndromes involving other genes, such as TP53. Most breast cancers occur in women without identifiable risk factors, and strong hereditary predisposition accounts for only 5% to 10% of cases. Often, the genetic component of disease predisposition may reflect small but measurable risks associated with polymorphic sequence variations at multiple loci. Breast cancer occurs in both young and old patients, and affects people of all races and ethnicities. Numerous other risk factors are associated with breast cancer development, including reproductive factors, dietary factors, obesity, and environmental exposure. Beyond the highly variable nature of breast cancer etiology, the malignant disease is also highly complex. Recent studies have dissected the molecular