Understanding chemotherapy: how it works, side effects and safety

Chemotherapy, often shortened to chemo, is a cancer treatment that uses medicines. It can sound frightening, and many people worry about side effects. This article explains in simple terms how chemotherapy works, how it is given, what to expect and when to call your care team. It uses information from the US National Cancer Institute, the NHS and the World Health Organization (WHO).

1. Introduction

Chemotherapy is a cancer treatment that uses medicines to destroy cancer cells ^{[1, 2]}. The WHO notes that treatment for cancer may include surgery, radiotherapy and systemic therapy, meaning medicines that travel through the body, such as chemotherapy, hormonal treatment or targeted biological therapy. It also stresses that an accurate diagnosis is essential because each type of cancer needs its own treatment plan ^[5].

Chemotherapy has several possible goals. According to the National Cancer Institute, doctors may use it to try to get rid of the cancer, to lower the chance that it returns, to slow its growth, or to shrink tumours that cause pain ^[1]. The NHS gives similar aims, including to lower the chance of the cancer coming back and to relieve symptoms, and says chemotherapy can be used on its own or with other treatments such as radiotherapy or surgery ^[2].

2. How chemotherapy works

Chemotherapy medicines kill or slow the growth of fast-growing cells. Cancer cells grow quickly, but so do some healthy cells, which is why chemotherapy causes side effects ^[1]. Healthy cells that divide quickly include those lining the mouth and bowel and the cells in hair follicles ^[1].

Chemotherapy is often combined with other treatments. It may be given before surgery or radiotherapy to shrink a tumour, afterwards to destroy cancer cells that may be left, or to help other treatments work better ^[1].

3. How it is given

The National Cancer Institute and the NHS describe several ways to give chemotherapy ^{[1, 2]}:

• Through a vein (intravenous). This is the most common way. A drip may run for 30 minutes to several days ^[2]. A long, thin tube called a catheter or a small disc under the skin called a port may be used, sometimes with a pump ^[1].
• By injection into a vein, muscle or under the skin, usually taking a few minutes ^[2].
• A wearable pump that gives medicine over a few days at home ^[2].
• Tablets or capsules taken at home, with regular check-ups ^{[1, 2]}.

Other routes described by the National Cancer Institute include injection into the space around the brain and spinal cord, into the abdomen, into an artery or as a cream on the skin ^[1]. Treatment can take place in hospital, at home or at a clinic as an outpatient ^[1].

Chemotherapy is usually given in cycles. A cycle is a period of treatment followed by a rest period so the body can recover. A course often lasts several months ^{[1, 2]}. The choice of medicines depends mainly on the type of cancer and how advanced it is, whether you have had chemotherapy before, and other health problems such as diabetes or heart disease ^[1].

4. Before treatment

Your care team will talk to you about the treatment and answer your questions. Each time you have treatment, they may ask about side effects, measure your height and weight, do a blood test to check how treatment is affecting your blood cells, and sometimes arrange an X-ray or scan ^[2]. The NHS gives these important points ^{[2, 3]}:

• Chemotherapy can harm an unborn baby. Tell your team if you might be pregnant, and use contraception during treatment.
• If having children matters to you, ask about storing eggs or sperm before treatment, because effects on fertility may be temporary or permanent.
• Ask which side effects to expect and how to prepare for them.

5. Side effects and how they are managed

Most people have some side effects, but not everyone has all of them. They usually begin a few days or weeks after treatment starts and often ease after it ends, although some can last longer or begin only after treatment finishes ^[3]. The NHS lists these common effects ^{[2, 3]}:

• Tiredness and low energy. The National Cancer Institute says fatigue is the most common side effect ^[1].
• Feeling or being sick
• A sore mouth and throat
• A weaker immune system, which raises the risk of infection
• Breathlessness and a fast heartbeat from anaemia (too few red blood cells)
• Easy bleeding or bruising
• Constipation or diarrhoea
• Temporary hair loss
• Numbness or tingling in the hands or feet
• Problems with memory and concentration
• Blood clots

Side effects do not show whether chemotherapy is working. Doctors check that using visits, blood tests and scans ^[1]. Side effects vary from person to person, even among people given the same treatment, and your health care team can treat them or talk with you about ways to reduce them ^[4]. Let your team know about every problem so that you can get the care you need ^{[3, 4]}.

6. Staying safe during treatment

The National Cancer Institute says it is best not to skip a chemotherapy treatment, but your doctor may change your schedule if you have certain side effects, and will explain what to do and when to start again ^[1]. It also advises telling your doctor or nurse if you have trouble eating ^[1]. The NHS says your care team can give you information about local support services, and that it can help to hear from other people with cancer, online or in person ^[3]. Please also tell your doctor about every medicine or product you use.

7. When to see a doctor

Contact your care team right away if you have ^[3]:

• a high temperature, or you feel hot, cold, sweaty or shivery
• signs of infection, such as a sore throat, cough, diarrhoea, frequent urination or pain when passing urine
• pain, swelling or warmth in an arm or leg
• sudden breathlessness, sharp chest pain, or coughing up blood

The NHS says these can be signs of an infection or a blood clot, which may need to be treated quickly. It advises that if you are not sure how to contact your care team, you should call its 111 helpline in the UK ^[3]. Ask your own hospital which number to use where you live.

In an emergency, call your local emergency number (112 in India, 911 in the United States).

8. Conclusion

Chemotherapy uses medicines to destroy cancer cells or slow their growth, and it is given in cycles with rest periods. Because it also affects some healthy cells, side effects are common, but they vary and your team can often help. Prepare by asking about side effects and fertility, report warning signs quickly and tell your doctor about everything you take. The choice of medicines and schedule is made by your cancer specialist.