To broaden your knowledge and understanding of chemotherapy and how each treatment chosen is unique for each patient and their cancer, Dr Ronwyn van Eeden explains what chemo is, how it works and why it is given.
Chemotherapies are drugs used to treat cancer, and hearing the words “You need chemotherapy” is often one of the most frightening statements for patients to hear. The fear is often based on the experience of others. Thus, giving rise to pre-conceived ideas that chemo is poison, or that it makes one sicker or extremely ill.
The first thing to remember is that not all chemotherapies are the same. It’s not a ‘one size fits all’. Medical oncologists tailor your chemotherapy regimen for your specific type of cancer. They take into consideration the type of cancer you have; the stage of cancer; age; overall well-being or performance status amongst other variables. It’s also an important factor whether you have other diseases, such as high blood pressure or diabetes. As well as what other cancer therapies you have received in the past.
Oncologists can give chemo either as a single drug or in combinations. Chemotherapy is used for different cancer types and in different settings to achieve different goals. Before chemo is administered, supportive medications are given to prevent nausea or drug reactions. These supportive medications have advanced over the years and are very effective in overcoming or preventing side effects from chemotherapy.
Goals of chemotherapy
The goal of chemotherapy is either to:
- Cure cancer.
- Control of the growth and spread which can make patients live longer.
- Palliate patients which means alleviating symptoms of cancer. For example, pain which can improve quality of life and make patients feel better.
Given for different reasons and in different settings:
• Neo-adjuvant chemotherapy – given before surgery or before radiation therapy to shrink a tumour and make it small enough to operate or radiate.
• Adjuvant chemotherapy – given after surgery or radiation to help kill remaining cancer cells or to prevent cancer from recurring.
• Palliative chemotherapy – given in very advanced stage cancers or incurable cancers to control symptoms and delay growth and spread.
Administration of chemotherapy
Chemotherapy can be given in different formulations. Most chemo is given intravenously (via a drip or a port) and some can be given orally as tablets.
The dose of chemo is worked out according to your body surface area, by doing a calculation that includes your height and weight. Sometimes doses can be adjusted according to the patient depending on their age and whether they have kidney or liver disease.
Some chemotherapies are given together with radiation. So, smaller doses would be used in this case. Chemotherapy doses can also be lowered if patients have low blood counts.
Chemotherapy is given at set intervals called cycles. Cycles differ according to which regimens are used to ensure optimal effectiveness of the drugs (can be weekly or every three weeks, for example). Sometimes it’s not possible to adjust the intervals. Especially, if the goal of chemotherapy is curative.
But, in palliative cases or advanced stages, the timing can be more flexible according to the patient’s well-being and how they tolerate treatment.
Different regimens also take different times to be infused. Some are as quick as 30 minutes, some can take up to four hours per cycle and some are even given in a pump over 24-48 hours that goes home with the patient.
It’s important that chemotherapy is administered in the correct way to effectively kill the cancer, while not causing intolerable toxicity or side effects.
How does chemotherapy work?
Chemo works by targeting cells at the different phases of development into new cells. This process is called the cell cycle. Because cancer cells form new cells quicker than normal cells, they are good targets for chemotherapy.
Side effects result from chemotherapy not being able to differentiate between normal cells and cancer cells. This can affect normal rapidly dividing cells in the body – such as hair, the lining (mucosa) in the mouth, and bone marrow – which is why patients can get alopecia (loss of hair), mucositis (mouth sores and ulcers) and low blood counts respectively. The doses and cycles given need to find a good balance between lessening side effects and effectively killing the cancer cells.
Grouping of chemotherapies
Chemotherapy drugs are grouped according to their chemical structure and origin of the drugs. They work in different ways at different points in the cell cycle. The major groups are called: alkylating agents; antimetabolites; anti-tumour antibodies – anthracyclines and non-anthracyclines; topoisomerase inhibitors, mitotic inhibitors; and steroids.
There are other types of chemotherapy as well.
In the next issue, I’ll go through each chemotherapy group; explain how they work; which cancers they are used for; and list the common side effects of each different kind.
MEET OUR EXPERT – Dr Ronwyn van Eeden
Dr Ronwyn van Eeden is a medical oncologist at the Medical Oncology Centre of Rosebank. She has a special interest in supportive care in cancer and new anticancer agents, especially immunotherapy.