Predictive Markers in Breast and Other Cancers: A Review‪.‬

A predictive marker can be defined as a factor that indicates sensitivity or resistance to a specific treatment. Predictive markers are important in oncology as different cancers vary widely in their response to particular therapies. Thus, for any specific type of cancer, only a proportion of patients will respond to a particular treatment (Table 1) (1-4), whereas most are likely to suffer from adverse side effects. For optimum patient management, it is therefore desirable to know in advance the likelihood of a tumor responding to the therapy under consideration. Predictive markers are sometimes confused with prognostic markers. Both types of markers are used to provide information on the likely future behavior of a tumor, but whereas predictive factors are used to prospectively select responsiveness or resistance to a specific treatment, prognostic factors provide information on outcome independent of systemic adjuvant therapy. Some markers can have both prognostic and predictive utility. For example, the estrogen receptor (ER) [1] in breast cancer not only predicts response to endocrine therapy but also correlates with good prognosis, at least in the short term. Whereas the use of markers for assessing prognosis has been widely discussed in recent years (5-7), there are few comprehensive reviews on predictive factors. The aim of this review is therefore to provide an overview on the current status of predictive markers in oncology. Because most work on predictive markers has been carried out on breast cancer, the main, but not exclusive, focus will be on this malignancy. The most widely studied predictive markers in oncology are now reviewed.