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Understanding Targeted Therapy
When it comes to cancer treatment, the most heard methods are traditional ones like radiotherapy (colloquially known as radiation therapy) and chemotherapy (often abbreviated as chemo). However, in recent years, targeted drugs and targeted therapy have increasingly come into the spotlight. But what exactly are these therapies? What does the term “targeted” mean?
In this article:
Drug Therapy
Principle
Like chemotherapy, targeted therapy also uses drugs to kill cancer cells in the patient’s body. However, while chemotherapy targets the characteristic that cancer cells divide faster than normal cells and thus theoretically affects all actively dividing cells, targeted drugs specifically interfere with particular molecules involved in the growth and survival of cancer cells, which are the “targets.” For example, certain types of genes and proteins that are especially advantageous for the development and spread of cancer cells are the focus of targeted therapy, which aims to prevent them from aiding cancer cell proliferation without affecting other normal tissues.
Target Types
Applicable Cases
Compared to radiotherapy and chemotherapy, targeted therapy is suitable for fewer cases and is not appropriate for all cancer patients. As the name suggests, the premise for the effectiveness of targeted therapy is that the patient’s tumor has the proper “target” for the drug to act upon. Leukaemia is one of the diseases that is suitable for targeted therapy in most cases. However, doctors may still need to take a sample from the tumor for testing to confirm the presence of the “target.”
Moreover, the same type of cancer may have cases that are suitable and unsuitable for targeted therapy. For example, only patients with HER2-negative breast cancer [Note 1] are ideal for targeted therapy, while targeted drugs for colorectal cancer are ineffective for patients with KRAS gene mutations [Note 2].
Therefore, in most cases, targeted therapy is used in combination with other treatments, and some patients may only take targeted drugs after ensuring they have no response to other therapies. Patients should consult their doctors to determine whether their condition suits targeted therapy.
Tailored Treatment
Drug Classification and Efficacy
Most targeted therapy drugs can be divided into two main categories: small molecules and monoclonal antibodies [Note 3]. Small molecules are chemically synthesized substances specifically designed to target molecules inside cells and can easily enter cells to eliminate them.
Monoclonal antibodies, on the other hand, are relatively larger immune system proteins that generally cannot enter cells and are only applicable to targets on the cell surface or periphery.
Since targeted therapy is a particular treatment, various targeted drugs are available, each with unique effects. Doctors will select the most appropriate targeted drug based on factors such as the patient’s cancer type, extent of spread, and personal constitution. Currently, targeted drugs mainly include the following categories:
- Signal Transduction Inhibitors
Signal transduction refers to the process by which cells respond to environmental signals. These drugs target molecules involved in signal transduction and block their activity. Even without external growth factors, some cancer cells continue to divide uncontrollably and rely on these drugs to interfere with inappropriate signal transmission.
- Angiogenesis Inhibitors
When a tumor grows to a specific size, it requires a blood supply to provide the necessary oxygen and nutrients, usually relying on new blood vessels. These drugs prevent the growth of new blood vessels, thereby stopping the continuous development of the tumor.
- Apoptosis-Inducing Drugs
Cells in the human body undergo a controlled death process called “apoptosis,” which helps the body eliminate unnecessary or abnormal cells. Since cancer cells can usually avoid apoptosis, these drugs are needed to induce the death of cancer cells.
- Immunotherapy Drugs
These drugs can activate the human immune system to destroy cancer cells. Some of these drugs are monoclonal antibodies that can recognize specific molecules on the surface of cancer cells. Once these monoclonal antibodies bind to the target molecules, the cells containing those molecules are destroyed. Other monoclonal antibodies can bind to specific immune cells to assist in killing cancer cells.
- Monoclonal Antibodies with Toxins
Some monoclonal antibodies carry toxic molecules. Once the antibody binds to the target cell, the poisonous molecule is taken up by the cell, ultimately leading to its death. However, the toxin does not affect most other cells in the body.
Targeted drugs can generally be taken orally or administered via intravenous injection. Patients at home can take the former, while the latter must be done in a clinic or hospital and can last 30 minutes to several hours.
Physiological Reactions
Side Effects
Although targeted therapy is specific and does not cover the entire body, like chemotherapy, it does not mean that patients will not experience side effects after the treatment. The following are some common side effects of targeted drugs:
- Nausea and vomiting
- Diarrhea and liver diseases, such as hepatitis and elevated liver enzymes
- Skin problems, such as acne-like rashes, dryness, and nail changes
- Blood clotting and wound healing issues
- High blood pressure
- Heart damage
In most cases, side effects will gradually disappear after healthy cells recover. If patients notice unusual side effects, or if the side effects persist for a long time or worsen, they should notify their doctor as soon as possible. Additionally, targeted drugs may cause defects in the fetus, so female patients should pay extra attention and inform their doctors whether they are pregnant or planning to become pregnant before taking targeted drugs.
Note 2: KRAS is a gene that promotes cell growth and survival. When it mutates, cell division becomes uncontrollable.
Note 3: Monoclonal (or single-strain) antibodies are antibodies produced by a single type of immune cell.
Department of Health, Drug Office
Hong Kong Breast Cancer Foundation
WebMD
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