Toxicity, side effects, and unpredictable effectiveness have been the hallmark of anti-cancer therapies used in the past to treat breast and other primary cancers. More recently, targeted therapies have been developed which reduce patient risk and provide remarkable improvement in patient outcomes.
A predictive marker can be defined as a variable which indicates the sensitivity or resistance to a specific treatment in an individual patient. Since response rates to various treatments can vary widely for any specific therapy, only a portion of patients will respond. Predictive testing provides results for one patient for a particular variable related to their individual disease status. In addition, predictive test results provide prognostic value, which is able to project an expected response of an individual patient to an indicated treatment. This very specific and individualized diagnostic information drives clinical treatment decisions, which then provide the most targeted treatment plan that has improved patient quality of life, morbidity, and mortality.