How targeted therapies are used to treat cancer

What is target therapy?

Targeted therapy is a type of cancer treatment that uses drugs designed to "target" cancer cells without affecting normal cells.

Cancer cells are usually genetically altered. Genes are parts of a cell's DNA that give certain commands to the cell. When a cell has gene changes, it does not "behave" like a normal cell. For example, gene changes in cancer cells can allow the cell to grow and divide very quickly.

 There are different types of cancer and in this sense, not all cancer cells are the same. For example, the cells in colon cancer and breast cancer have different gene alterations that help the growth or alteration processes. Even among different people with the same general type of cancer (such as colon cancer), cancer cells may have different gene alterations, making the specific type of colon cancer different in different people.

Scientists have also discovered that the environment in which different species cancer  develop is not always the same. For example, some cancers have certain types of proteins or enzymes that send specific messages to signal the cancer cell to grow and copy itself.

Knowing these features in detail has led to the development of drugs that can "target" these proteins or enzymes and block the messages sent to the cells. Targeted therapies can block or turn off signals that make cancer cells grow, or they can signal cancer cells to self-destruct.

Target therapy is an important type of treatment for cancer and scientists continue to develop even more effective drugs as they learn more and more about specific changes in cancer cells.

At this time, only a few cancers are routinely treated with targeted therapy alone. Most people receiving targeted therapy also need additional treatment - surgery, chemotherapy, radiation therapy or hormone therapy.

How does targeted therapy differ from chemotherapy?

Target therapy drugs, like other drugs used to treat cancer, are technically considered chemotherapy. But targeted therapy drugs do not work in the same way as traditional or standard chemotherapy. Target drugs target some of the changes that make cancer cells different from normal cells. This makes them work differently from chemotherapy in two key ways:

Because of their targeted action, these drugs have an effect on cancer cells and mostly do not affect normal, healthy cells. Traditional chemotherapy is cytotoxic to most cells, which means it can damage normal, healthy cells in addition to damaging and killing cancer cells.

Targeted drugs often work by blocking cancer cells from reproducing. This means they can help stop the cancer cell from dividing and creating new cancer cells. However, traditional chemotherapy kills cancer cells that already exist.

How target therapy works

Target therapies are made to detect and attack specific areas or substances in cancer cells. They can detect and block certain types of messages sent inside the cancer cell that signal the cell to grow. Some of the substances in cancer cells that become "targets" of targeted therapies are:

• Too large an amount of a certain protein in a cancer cell
• A protein in a cancer cell that is not found in normal cells
• A protein that has mutated in a cancer cell
• Gene (DNA) changes not found in a normal cell

The action of target drugs can work for:

• Blocking or turning off the chemical signals that tell a cancer cell to grow and divide
• Changes in proteins in cancer cells so that the cells are destroyed
• Stopping the creation of new blood vessels to feed cancer cells
• Triggering the immune system to kill cancer cells
• Carry toxins to cancer cells to kill them, but not to normal cells

The action of medicines can affect where these medicines act and what side effects they cause.

It is important to note that some targeted therapy drugs, such as monoclonal antibodies, work in more than one way to control cancer cells and can also be considered immunotherapy as they boost the immune system.

Target therapy as precision medicine

Targeted therapy is sometimes called precision medicine or personalized medicine. This is because these therapies are made to target specific changes or substances in cancer cells, and these "targets" can be different even when people have the same type of cancer.

Some types of tumors are tested for different targets after biopsy or surgery, and this process can help find the most effective treatment. Finding a specific target for target therapy makes patient treatment more precise and personalized.

Some targeted drugs are more specifically targeted than others. Targeted therapies are classified as small or large molecule drugs.

Small molecule drugs are small enough to penetrate a cancer cell once they find it. They work by targeting a specific substance inside the cell and blocking it.

Large molecule drugs usually cannot penetrate the cell. They act by attacking and then weakening or destroying proteins or enzymes on the surface of the cell. They are often described as 'lock and key' as the molecule acts as a key that opens the enzyme or protein on the cell surface like a lock. The key successfully enters the lock, allowing the drug to act.

Types of target therapy

Many cancers can be treated with targeted therapies and there are many different types of targeted therapies. Here are some types with some examples of how they are used:

Angiogenesis inhibitorsA: They block the formation of new blood vessels that feed and nourish cancer cells. Example: bevacizumab (used in various cancers).

Monoclonal antibodiesA: They can deliver molecules by themselves or molecules with drugs into or onto the cancer cell to kill it. Examples: alemtuzumab (some chronic leukemias), trastuzumab (some breast cancers), cetuximab (for some colorectal, lung, head and neck cancers). NOTE: Some monoclonal antibodies are called target therapy because they have a specific target on a cancer cell that they seek to detect, attach to, and attack. But other monoclonal antibodies act like immunotherapy because they make the immune system respond in a timely manner, allowing the body to detect and attack cancer cells more effectively.

Proteasome inhibitorsA: They disrupt normal cell functions so that cancer cells die. Example: bortezomib (multiple myeloma)

Signal transduction inhibitorsA: They disrupt cell signals so as to alter the actions of the cancer cell. Example: imatinib (some chronic leukemias)

Photo: https://www.facingourrisk.org/info/risk-management-and-treatment/cancer-treatment/by-treatment-type/targeted-therapy/overview