Understanding chemotherapy

Dr Sze Wai Chan recaps on how chemotherapy kills cancer, why the side effects occur and what the side effects are likely to be.

How does chemotherapy kill cancer?

Chemotherapies are molecules that kill fast-growing cells. When patients have cancer, the fastest growing cells (abnormal cells) are within the cancer.

When abnormal cells are “growing”, they undergo a process called mitosis, which sees them divide or replicate themselves. One abnormal cell becomes two abnormal cells, and two abnormal cells become four, and so on. Eventually forming a noticeable mass, which we call a tumour.

The core of these tumour cells – the DNA (the genetic material that stores messages) – replicates itself in the process of mitosis and sends the abnormal growth signals, causing cancer to progress.

Some chemotherapies break DNA while others stop the DNA enzymes (or catalyst) from working.  Cancer DNA therefore, is broken and the abnormal growth signals cannot be transmitted, stopping the growth process and stalling mitosis. Another type of chemotherapy can “freeze” or “intoxicate” mitosis.

A number of chemotherapies can also look like DNA building blocks. When these chemotherapies are inserted into the DNA, the message transmitted from these aberrant DNA would be useless, stopping the cancer from multiplying.

Cancer cells are the fastest or faster growing cells in the body. As a results, they divide/replicate more often than normal cells. Therefore, when chemotherapy is given, it predominately kills cancer cells during mitosis.

How does chemotherapy cause side effects?

Knowing how chemotherapy works, other innocently growing cells in our body can be damaged because they also undergo mitosis for normal repair and renewal. Therefore, it is not uncommon to have the following general side effects:


Most of the side effects mentioned above are reversible, as they’re all normally growing cells that can repair themselves. Fertility, however, can be permanently impaired. Therefore, it is vital for patients who wish to remain fertile, to preserve their fertility by seeking expert advice prior to starting chemotherapy.

Unpleasant side effects such as fatigue, nausea and vomiting, will usually resolve within one week.  The period of decreased immunity usually occurs within days 5-10 after chemotherapy. This is the period where infection can creep in, and patients must be vigilant of signs of infection, such as fever.

White cell growth factors (e.g. Neupogen and Neulasta) are available to support low white cell counts after chemotherapy. These act to boost the bone marrow to produce white cells faster, shortening the time to recovery and minimising the risk of infection. Scalp cooling during chemotherapy infusion is an option for patients who would like to minimise hair loss.

Specific side effects

There are specific side effects to certain groups of chemotherapy. For example, the taxane group of chemotherapy, such as paclitaxel and docetaxel, can cause sensory peripheral neuropathy, giving rise to pins and needles sensation in the fingers and toes. This side effect usually develops with increasing dose. It is reversible, but it may take time to resolve.

The anthracyclines group, such as adriamycin, can cause heart damage when the dose exceeds the upper limit. The dosage of this chemotherapy is usually capped to avoid this toxicity.

One of the platinum chemotherapies, oxaliplatin, can cause cold neuropathy, where a particularly unpleasant sensation is induced by exposure to cold objects, like drinking icy drinks. Avoidance of anything cold usually solves the problem.

These are the common side effects of chemotherapy. However, during the consultation with your oncologist, please enquire about the expected side effects and the associated management of the planned chemotherapy. With prompt treatment, most side effects are manageable and reversible.

Written by Dr Sze Wai Chan.