Chemotherapy

What is chemotherapy?

Chemotherapy refers to drugs commonly used to treat cancer. It uses potent chemical compounds to kill cancer cells in the body.

Cancer cells are the fast-growing, malignant mutant versions of normal body cells. Without effective treatments such as chemotherapy to suppress cell growth and/or kill these cell types, cancerous cells eventually outgrow the body’s immune system and cause harm.

Why is chemotherapy used as a cancer treatment?

Chemotherapy is an integral part of cancer treatment, especially in later stages when cancer cells have spread from the original tumour location to other body parts (metastasized). Unlike surgery or radiotherapy which focus on “local” tumours, chemotherapy can simultaneously target cancer cells all over the body as these drugs circulate in the bloodstream – this makes chemotherapy an excellent choice for systemic treatment of cancer.

At what stage of cancer is chemotherapy used?

An oncologist – a cancer specialist – may prescribe chemotherapy for cancers of all stages. It may be given alone or in combination with radiotherapy or surgery to improve treatment outcomes.

As chemotherapy drugs enter the bloodstream, they are dispersed quickly to various locations to exert their anticancer effects. As such, chemotherapy is routinely used for many cancer patients with metastasized cancer.

Many patients with stage 2 or 3 breasts, colon, gastric or lung cancer may benefit from chemotherapy too as doctors rely on chemotherapy to eradicate the small number of cancer cells that have been shed from the original tumours and spread to other body parts via the blood or lymph nodes. These micrometastases (“micro” means tiny) are too small to show up in conventional imaging tests but they are extremely important to eradicate. Chemotherapy plays an important role in “cleaning up” remnants of these micrometastases.

There are many types of chemotherapy. Each chemotherapy has a unique mechanism of action and is suited to different cancer types or patient conditions. In some situations, combining different chemotherapy that works in different ways enhances treatment efficacy. The oncologist will discuss the best possible option with you based on your unique circumstances.

Chemotherapy drugs can be administered via different routes, including:

• Intravenous infusion: Chemotherapy is most commonly given as an infusion into the vein. The doctor or nurse will insert a tube with a needle into a vein in your arm or into a device attached to the vein in your chest.
• Oral administration: Some chemotherapy drugs can be taken in tablet or capsule form.
• Special administration routes: Sometimes the oncologist will target a specific area of the body where cancer cells are found. Chemotherapy drugs can be delivered directly to that one region. For example, we can deliver drugs into the space within the abdomen (intraperitoneal chemotherapy), the fluid surrounding the spine (intrathecal chemotherapy), or into the bladder (intravesical chemotherapy).
• Chemotherapy creams: There are instances where chemotherapy can be delivered by applying creams or gels onto the skin. These are usually used to treat skin cancers.

How does chemotherapy work?

Chemotherapy drugs work in different ways but all of them have a central effect: they target the cell cycles and kill cells that are replicating.

The cell cycle is a series of phases that a cell goes through as it grows and develops in order to become fully functional. Cancer cells typically have a much faster cell cycle – a competitive edge over other healthy cells. Chemotherapy drugs exploit this biological advantage to cause more damage to cancer cells as they divide.

However, these drugs cannot fully differentiate between healthy and cancerous cells. This means some healthy cells will be impacted during treatment. Fast-growing normal cells such as those of the skin and hair are most affected. This is why chemotherapy may produce undesirable side effects such as hair loss.

Chemotherapy drugs

Chemotherapy drugs are often grouped based on their mechanism of action and chemical composition. Each group targets cancer cells at different stages of cell division.

• Alkylating agents: These drugs disrupt the DNA of cancer cells to prevent them from replicating. Alkylating agents are the oldest type of chemotherapy. Common examples include cyclophosphamide and cisplatin.
• Antimetabolites: These drugs interfere with cell metabolism to halt cancer growth. Antimetabolites are commonly used against leukaemia and breast cancers and include drugs such as 5-fluorouracil and methotrexate.
• Anthracycline: Anthracyclines are antibiotics first extracted from bacteria that have anticancer properties. They bind with DNA so it cannot make copies of itself, and the cancer cell cannot reproduce. Common examples include doxorubicin and daunorubicin.
• Topoisomerase inhibitors: These drugs interfere with enzymes called topoisomerases, which help separate the strands of DNA so they can be copied. Drugs in this group include etoposide and irinotecan.
• Mitotic inhibitors: These drugs stop the process of cell division (mitosis) by interfering in the production of essential proteins (tubulins). Mitotic inhibitors include docetaxel, paclitaxel, and vinblastine.
• Nitrosoureas: These are alkylating agents that can travel into the brain. This unique feature makes them useful to treat certain types of brain cancer. Examples of nitrosoureas include carmustine and lomustine.
• Corticosteroids: These are natural hormones or hormone-like compounds that are useful to treat cancer. Doctors may use them to prevent nausea and vomiting too. Common corticosteroids include prednisone and dexamethasone.

What do I need to know about chemotherapy’s side effects?

It is common to worry about chemotherapy’s side effects, but sometimes they may not be as bad as you might expect.

Side effects from chemotherapy experienced by each person can vary greatly between individuals. Some chemotherapy may cause more side effects than others.

Your doctor will discuss which chemotherapy is best for you. They will select an optimal treatment that is effective but has the least side effects. Concurrent use of drugs that cause similar side effects is generally avoided.

Common side effects of chemotherapy

Here are some of the more common side effects of chemotherapy that you may experience:

• Fatigue
• Hair loss
• Nausea and vomiting
• Diarrhoea
• Loss of appetite
• Mouth sores and pain with swallowing
• Easy bruising
• Bleeding
• Changes in libido and sexual function

Each chemotherapy has its own unique side effect profile. Most of these side effects are temporary and will subside once chemotherapy ends. Specific chemotherapy drugs may damage cells in the heart, kidneys, bladder, lungs, and nervous system. Special precautions and supportive measures are usually taken when these drugs are used.

Your cancer care team will provide the necessary information and support you throughout chemotherapy but the appearance of new side effects or changes in severity should not be taken lightly. Some side effects may be signs of greater problems and you should notify your doctor promptly.

How to minimise chemotherapy side effects?

Here are some tips to minimise side effects and improve your overall chemotherapy experience.

Fatigue: Frequent rest or short naps during the day may help to alleviate some fatigue. Light exercise such as a short walk goes hand-in-hand with sufficient rest to boost energy. Sometimes, chemotherapy may induce anaemia or low levels of red blood cells. Your doctor can perform blood tests to diagnose anaemia and treat the condition.

Hair loss: Not all chemotherapy causes hair loss. But if you notice your hair begins to thin, you may want to change to a mild shampoo or use soft hair brushes. Sometimes the scalp becomes sensitive and feels tender. You should protect it from direct sunlight or frequently use sunscreen. Alternatively, you can consider wearing a cap, scarves, turbans, or a wig.

Nausea and vomiting: Some changes to the dietary pattern can help to ease nausea and vomiting. You should eat smaller portions but have multiple meals throughout the day. Food that causes a queasy stomach, such as fried or fatty food, should be avoided. Some doctors may prescribe anti-nausea medications if your symptoms persist.

Mouth ulcers: Painful ulceration of the mouth (mucositis) can be a side effect of chemotherapy. Your doctor can give you a special mouth wash to ease the pain and promote healing. For some patients, the doctor may change the chemotherapy too. It is important to always maintain good oral hygiene.

Many patients wish to complement chemotherapy with herbal or dietary supplements. However, chemotherapy drugs and complementary or alternative medicine may interact and cause adverse effects.

Certain supplements will affect the concentration of chemotherapy in the blood. This often happens because the supplement interferes with drug metabolism or modifies the action of some crucial enzymes. Chemotherapy drugs are compounds with narrow therapeutic windows (which means a slight change in blood concentration will cause a disproportionate impact on treatment outcome), unintended alteration of blood concentrations may lead to serious health issues.

For example, green tea extract (scientifically known as epigallocatechin gallate, or EGCG) is known to interact with chemotherapy drugs such as irinotecan and fluorouracil, leading to an increase in the drug concentration in the bloodstream and potentially causing toxicity.

Another popular supplement, St. John’s Wort, interacts with many chemotherapy drugs too, including irinotecan, methotrexate, and docetaxel. Some reports linked the consumption of turmeric with liver toxicity when taken together with paclitaxel.

Chemotherapy drugs may interact with some common over-the-counter medications such as folic acid (vitamin B9) and NSAID painkillers (e.g. ibuprofen). NSAID slows kidney clearance of many chemotherapies (e.g. methotrexate), leading to pronounced side effects. Consuming a high level of folic acid may reduce the effectiveness of certain chemotherapy, particularly those that aim to disrupt the effects of folic acid (antifolate chemotherapy, such as methotrexate and pemetrexed).

Please inform your doctor or pharmacist about any dietary supplements or over-the-counter medications you are taking. These include herbal, traditional, or home remedies as well as vitamins and minerals.