If and how a cancer treatment will work to kill a tumor and rid the body of cancer depends on many factors. Research has well established that changes in the DNA can allow uncontrolled cell growth, resulting in the development and expansion of a tumor.

Mutations in specific genes — among the best known are TP-53, EGFR — or an overabundance of a protein like the estrogen receptor or HER2, also contribute to determining if a therapy will be effective. Increasing evidence is now pointing to another key factor that can alter responses to treatment: the place where the tumor resides, also known as the tumor microenvironment.

What is the tumor microenvironment?

A tumor is surrounded by many cells, including normal tissues, blood vessels, and inflammatory (or immune system) cells. Together these tumor and other cells create a specific environment, or microenvironment, that influences the cancer growth. The microenvironment can be and often is different from the normal cellular environment. There could be increased fluid or the cell membranes may be stiffer. Extra cells that are not present in healthy sites can be found in abundance. All these cells interact with the tumor just as the tumor can interact with these surrounding cells. For example, if the immune cells in this microenvironment express a protein called PDL-1, the patient may benefit from immunotherapy that specifically attacks PDL-1.

Why do scientists care?

As we learn more about the similarities and differences of the tumor microenvironment, scientists can develop better tools to specifically attack the tumor. They can develop drugs to attack a specific protein or use radiation to change the expression of an immune protein or use cell stiffness to identify cancer cells.

Research into the tumor microenvironment and how to harness it in cancer treatment is still in the early stages. Clearly, it is playing a key role in determining outcomes, but more must be learned to identify how current treatment including radiation, chemotherapy, immunotherapy and surgery alter its makeup and role in cancer cell growth.