Targeted cancer treatments

Published in Medicinewise Living

Date published: About this date

In Australia, 1 in 2 men and 1 in 3 women will be diagnosed with cancer before age 85. Treatment for many will include chemotherapy — the use of medicines that can slow or stop cancer cells from dividing and spreading.

Chemotherapy medicines can improve your chances of recovery and survival from cancer, but they can also cause hair loss, fatigue, vomiting, and other potentially harmful side effects. During the past decade a number of newer medicines — known as targeted anticancer therapies — have been developed that focus more of their effects on cancer cells than on other parts of the body.

It's chemotherapy, but not as we know it

Cancer cells behave abnormally, multiply uncontrollably, and eventually change other cells around them to make their environment more ‘cancer friendly’.

Many chemotherapy medicines treat cancer by being poisonous (cytotoxic) to cells that multiply rapidly. A lot of side effects linked with cytotoxic chemotherapy occur because these medicines can’t always tell the difference between normal cells and cancer cells. This is because some normal cells in our body also multiply rapidly as part of their job in keeping us healthy. This includes cells that form our skin, hair, nails, and the lining of the gut.

Targeted anticancer therapies work differently. They recognise features of a cancer cell that make it different to normal cells in the body. Being more specific means these therapies can damage cancer cells as effectively as cytotoxic chemotherapy, but with different and often less-severe side effects.

How targeted therapies target cancer

Research has shown us that cancer cells produce certain molecules that help them to multiply and grow more easily. Cancer cells can also 'look' different to normal cells. This information has given scientists new ways to stop cancer cells from growing, or at least slow their spread through the body.

Several monoclonal antibodies and small molecule therapies have been designed to target cancer cells in different ways. Currently these medicines work by:

  • interfering with enzymes that control the activities of cancer cells, including growth
  • changing certain molecules inside a cancer cell so that it dies
  • ‘starving’ cancer cells, by stopping the formation of blood vessels that feed the cancer.

Can targeted therapies cause side effects?

Although they are less likely to affect normal cells in the same way cytotoxic chemotherapies do, targeted therapies — like all medicines — can still cause side effects. These often depend upon the molecule being targeted, and can include skin changes (such as a rash, dryness or itchiness), high blood pressure (hypertension), wound healing problems and bleeding/clotting issues. Some therapies (e.g. lapatinib and trastuzumab used to treat some breast tumours) can cause damage to heart muscle cells.

Because of the potentially serious nature of some side effects, a person taking a targeted anticancer therapy may require careful and regular monitoring during treatment.

Not everyone will get side effects, but some people may have many, or may experience a serious effect that needs urgent medical attention. It is important to always discuss the possible side effects of any medicine with your doctor or other health professional — and let them know about any changes in how you feel during treatment.

How effective are targeted therapies?

Targeted therapies are able to treat some cancers on their own — or they might be combined with other chemotherapy, surgery or radiation to improve the effectiveness of treatment.

However, because they mostly control rather than destroy tumours, targeted therapies won’t be suitable for everyone with cancer. Even when used in people with the same type of cancer, targeted therapies may not always be effective for everyone because actual cancer cells can be different between individuals.

For example, some breast cancers have molecules called HER2 sitting on the cell surface. This molecule is targeted by a monoclonal antibody therapy called trastuzumab. Giving trastuzumab to someone who has breast cancer cells that do not make HER2 will have no benefit — and may instead cause them harmful side effects.

For both cytotoxic chemotherapy and targeted therapies there is also a risk that a cancer can become resistant to treatment. If this happens, the medicine being given will no longer stop the cancer growing or spreading.

Are targeted therapies right for me?

Targeted therapies provide further treatment options for many people with cancer, including those with rarer cancers that have few, if any, therapies available.

Before you can be prescribed a targeted therapy, your doctor may need to perform a diagnostic test to confirm that your cancer will respond to treatment. The test will show if the cancer cells carry a molecule that can be targeted by one of these newer medicines.

Even still, a targeted therapy might only be prescribed if other options aren’t available or are unsuitable for you — or because your cancer is very advanced or not responding to other treatment.

Discuss all your treatment options with your doctor so you understand the benefits and risks. Targeted therapies may be right for you, but they are still relatively new medicines, and their effectiveness may not have been tested as widely as other cancer treatments. Over time as more clinical trials are run, and more diagnostic tests are developed, targeted therapies are likely to offer more treatment options for more people with cancer.

Snapshot of targeted therapies

At present, most targeted therapies include monoclonal antibodies and small molecule therapies. Cancer vaccines and gene therapies are also being investigated.

Monoclonal antibodies

Monoclonal antibodies behave just like the antibodies our body makes naturally to fight off foreign substances (antigens), like viruses and bacteria. Each anticancer monoclonal antibody locks onto a specific molecule sitting on the surface of a cancer cell. Once the antibody has attached, the molecule stops working. This directly interferes with the cancer cell and, in some cases, switches on the immune system so it attacks the cell.

Monoclonal antibody therapies include:

Different monoclonal antibodies may be used for different cancers, including some types of breast cancer, leukaemia, lymphoma, and melanoma, and some colorectal, gastric, and head and neck cancers.

Small molecule therapies

These therapies are so small they are able to slip through the outer lining of a cancer cell and get into the inner workings. Like monoclonal antibodies they are designed to attach to specific molecules, like enzymes that control cell growth, to stop the cell from working.

Small molecule therapies include:

As with monoclonal antibodies, different small molecule therapies may be used for different cancers. These include some types of breast cancer, leukaemia, lymphoma, melanoma, multiple myeloma, as well as cancers in various organs and tissues, including the bone marrow, kidneys, liver, lungs, pancreas, and thyroid gland.

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