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Targeted therapy is a way of treating cancer using drugs designed to target cancer cells, with minimal effect on normal cells. This is achieved by blocking specific molecular targets, usually altered genes or proteins specific to cancer cells, that are driving cancer cells' growth. These molecular alterations can occur on the surface of cancer cells, inside the cells or in the area around the tumour. This tailored form of treatment is sometimes called precision medicine as it targets specific changes or substances in cancer cells.
The poster child of targeted therapy is Imatinib, a drug that shuts down the activity of an abnormal gene, known as the BCR-ABL gene, which is found in chronic myeloid leukaemia (CML). The development and subsequent use of Imatinib has transformed the treatment of CML, changing it from a routinely fatal leukaemia to a disease where over 95% of the patients survive more than 5 years.
Since then, a better understanding of various cancers and the discovery of new drugs have rapidly expanded the targeted therapy options for many cancers. Most patients who receive targeted therapy also undergo other forms of treatment such as surgery, chemotherapy or radiotherapy to achieve better results.
Targeted therapy has found success in many cancer types, including lung, breast, colorectal, skin and leukaemia. However, it is only suitable for some cancers, as not all cancers have molecular targets. Even within the same type of cancer, the molecular targets may differ from one patient to another. For that reason, an important step in assessing whether a patient is suitable for targeted therapy is molecular testing for specific actionable gene or protein alterations. These tests look for the existence of specific genes or changes in protein structure on the cancer cells that can be acted upon by medications. This will allow patients to be matched with the most effective treatment.
You may need to undergo surgery or biopsy – a procedure where your doctor removes a piece of the tumour for testing. Alternatively, in advanced cancers, cancer cells may shed fragments of abnormal cancer cells DNA into blood circulation. These can be captured and analysed for molecular alterations. Molecular testing has improved significantly in recent years. Multiple alterations can be tested concurrently on small specimens, to produce results within a shorter timeframe.
Your doctor will inform you whether targeted therapy is suitable for you.
Different types of targeted therapy act on different molecular targets associated with cancer. They stop the cancer cells from growing by:
Some types of targeted therapy work in more than one way to stop cancer growth.
Targeted therapy can be given in different ways:
There are specific ways each treatment is administered. If your doctor decides to prescribe oral targeted therapy, you should take note of the dosage, frequency of administration, timing of administration with regards to food and whether there is a routine treatment break in each cycle. You should discuss with your cancer team about any concomitant usage of other medications and supplements even for unrelated health conditions. Some treatments may require routine supportive medications such as moisturising cream or antidiarrheal medicines.
You need to take certain precautions when receiving targeted therapy. This is to protect your family and friends from unnecessary exposure to cancer drugs.
If you are given oral targeted therapy to take at home, you should not let your family members or friends come into contact with the medication. Sometimes this may also include contact with your body fluids while you undergo treatment (or for a time after completing treatment).
Targeted therapy is now used to treat many kinds of cancer. A few examples are shown below:
There are many types of targeted therapy. The potential side effects of targeted therapy depend on which targeted therapy drug you are given and the drug targets. Some targeted therapy has minimal side effects whilst others may lead to uncommon but serious problems. Side effects also vary from one person to another.
Side effects of targeted therapies may include:
Some targeted therapies may have unique side effects not covered in the list above. Your doctors will advise and monitor you for these side effects.
It is important to note that not every person will experience every side effect and the type and severity of these side effects vary from patient to patient. Most of these side effects can be managed with supportive measures. In some cases, your doctor may reduce the dosage of your medications. Please monitor your condition and notify your cancer care team if unexpected side effects occur.
Most side effects of targeted therapy such as rash, high blood pressure and diarrhoea improve soon after stopping drugs. Some uncommon but serious side effects such as blood clots and changes to heart function may have more long-term effects. Talk to your cancer care team if you have any concerns about side effects, and be sure to report all changes in side effects to them.
You may wish to complement your targeted therapy with herbal or dietary supplements but before you do so, you must discuss it with your doctor or pharmacist as some of these supplements may interact with your cancer therapy.
Certain supplements will affect the concentration of anticancer medication in your blood. This often happens because the supplement interferes with drug metabolism or modifies the action of some crucial enzymes.
For example, a popular supplement St. John’s Wort interacts with imatinib by increasing the drug clearance from the body. Taking these two together may reduce the effectiveness of imatinib.
Additionally, ginseng (Panax ginseng) has been shown to interact with imatinib, and possibly cause liver toxicity. Because ginseng has estrogenic effects, you should consult your doctor if you have hormone-sensitive cancers.
Your doctor will likely recommend a targeted therapy when laboratory tests show that your tumour contains certain markers that will respond to a targeted therapy drug. Certain cancers exhibit specific markers for which there is still no suitable drug yet, so not all cancers can be treated with targeted therapy.
Oral targeted therapies are increasingly used to treat cancer as these can be taken at home by the patients. Their use is comparatively more straightforward than other infusion drugs, but it does not mean oral targeted therapies are inferior in efficacy against cancer as each drug has its unique potency.
During your routine clinic visits, your doctor will order specific blood tests and scans to check whether the cancer has responded to the targeted therapy. If the treatment response is good, scans will show that the tumour has shrunk or even disappeared completely. Sometimes the tumour may remain similar in size (not progressing, stable disease), this also suggests that the disease has responded to the treatment too.
You are more likely to have hair loss with chemotherapy while targeted therapy may cause hair thinning.