Predictive markers or predictive testing can sometimes be confused with prognostic factors. While both types of information do assist in providing information on the likely progression of a patient's disease, the terms prognostic and predictive differ in the following way:
- Prognostic factors, such as metastases, invasiveness of the tumor, and age help to provide the rest of the picture to assist in projecting the overall outcome from the treatment or therapy (prognosis).
- Predictive markers/testing are used to select patients who are most likely to respond positively to a specific treatment.
Though it is important to understand the differences in meaning between predictive and prognostic, it is true that a select few tests can provide both predictive and prognostic value. For example, estrogen receptor (ER) testing in breast cancer can be used to both predict response to a specific hormone therapy and is a factor that correlates closely with favorable short term prognosis.
The list below shows the most prevalent and commonly applied predictive testing methods used to identify various subtypes of human breast cancer. The results of these tests provide specific information used to determine specific treatment decisions for these tumors.
- ER by immunohistochemistry (IHC)
- Progesterone receptor (PR or PgR) by IHC
- Human epidermal growth receptor 2 (HER2 or HER2/neu) by IHC or HER2 amplification status by in situ hybridization (ISH), chromogenic in situ hybridization (CISH), or fluorescent in situ hybridization (FISH)