Oncotype DX®

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Oncotype DX®

Understanding Gene Expression

All cancer is genetic in some way. However, most cancers aren't the kind you inherit. This may seem contradictory at first. The difference lies in understanding when the gene changed the way it works — a change before birth that you inherit from a parent or mistakes that buildup each time your cells copy their genes, to make new cells.

Traditional genetic testing looks at genes you inherit from your parents. It usually targets one gene and looks for specific changes or mutations in the genetic code that you were born with.

On the other hand, gene expression has little to do with heredity or the genetic code. It looks at what the genetic code is making, but not at the code itself. Genes act as instructions to make specific proteins. Gene expression testing measures how active certain genes are. It may help to think of gene expression as a light switch, with a dimmer control. Taking a step back, think of the light bulb itself as the genetic code. This is what is inherited, and doesn't change. However, what that light does in each cell will change. Sometimes the light is turned on to full power. Other times, the light is completely off. Gene expression is the dimmer that controls the light.

When a gene is very active, it has a high expression level. The light is turned fully on. When a gene isn't active, it has very low expression. The dimmer switch toned the light down.

Each tumor and cancer has its own unique gene expression pattern. Each gene contributing to that cancer has its own dimmer switch. Gene expression levels within a tumor may affect how a cancer grows and how it will respond to treatment.

Step 1. These are the genes we inherit. Testing for inherited forms of breast cancer looks here.
Step 2. This is where gene expression is controlled.
Step 3. This is the product of gene expression. Gene expression testing looks here.

Traditional genetic testing for inherited genes takes place at Step 1. Gene expression testing doesn't happen until Step 3. Therefore, gene expression testing doesn't look at genes you inherit — only what the gene is actually making.

Next: Treating Early-Stage Breast Cancer