Breast Cancer Biomarkers

There are numerous additional biomarkers under investigation. It is important to note that different biomarkers are likely to be useful for different reasons. Some biomarkers may help predict or determine responses to particular treatments and others may be useful in predicting how aggressive a particular cancer may be. Still other biomarkers are being tested as new diagnostic tools, for early detection of breast cancer.

Biomarkers can be found in the tumors themselves or in blood, urine, feces or even in breath samples.
They can be made of protein, RNA, or smaller biochemicals. Some biomarkers are actually measures of larger 'states' of the cell, including the stability of the chromosomes. There are too many under investigation to list them all here, but they include: Ki67 (a protein marker of cell division), chromosome length, and some microRNAs. For more details, see http://www.ncbi.nlm.nih.gov/pubmed?term=breast%20cancer%20biomarkers .

A biomarker is something that provides information (often indirectly) about a biological process or event. An example is elevated cholesterol. High cholesterol is frequently associated with coronary heart disease and so is a biomarker for heart disease.

With respect to cancer, there are different types of biomarkers that are used to guide treatment. In breast cancer, there are several that are routinely checked by pathologists.

An example using the estrogen receptor (ER): The estrogen receptor is a protein the binds to estrogen (when it is present). Once they are bound together, the receptor:estrogen duo can cause the activation/repression of a variety of genes, altering cellular activity. In general, estrogen acts as a growth factor for breast cells. When breast cancer is diagnosed, the cancer is examined for the presence of the the estrogen receptor. If it is present, that is an indication that the cancer cells are still 'listening' to the signals sent via estrogen. If the ER is NOT there (but the cells are still dividing - causing the cancer), it is an indication that the cells are more abnormal. They no longer require the signals provided by estrogen.

What does this mean for the patient?
Breast cancers that express the estrogen receptor (ER positive) may respond to treatments that block estrogen production/activity (i.e. tamoxifen).
ER negative tumors may be more aggressive and are not nearly as likely to respond to ER blockers (antagonists).

Other biomarkers in breast cancer include the HER2 protein (a growth factor receptor) and the progesterone receptor (PR).

The identification of biomarkers allows clinicians to personalize the treatment of individual patients, based on their molecular profiles.