What chemotherapy is — and is not
Chemotherapy ("chemo") is a group of medicines that damage cells while they divide. Because cancer cells divide more often and repair themselves less well than most normal cells, they are hit hardest. Some normal cells that also divide quickly — in the bone marrow, the lining of the mouth and gut, and hair follicles — are affected too, which is why the common side effects are low blood counts, mouth soreness, nausea and hair loss.
Chemotherapy is not one drug. There are dozens of agents with different targets, schedules and side-effect profiles, and most regimens combine two or more. It is also not automatically the first or only treatment: for many cancers today, targeted therapy, immunotherapy or hormone therapy may be used instead of, before, or alongside it.
When chemotherapy is considered
- Before surgery (neoadjuvant) — to shrink a tumour so that surgery is smaller or possible, and to see early how the cancer responds. Common in breast, oesophageal, rectal and some head-and-neck cancers.
- After surgery (adjuvant) — to reduce the chance of the cancer returning by treating cells that may already have spread but cannot be seen on scans. Common in breast, colon and lung cancer when the risk of relapse is high enough to justify it.
- With radiation (chemoradiation) — some drugs make cancer cells more sensitive to radiation. Used in cervical, head-and-neck, oesophageal, anal and some lung cancers.
- As the main treatment — for cancers that respond well to systemic treatment (many lymphomas and leukaemias, germ-cell tumours) and for cancer that has spread, where the aim may be control and comfort rather than cure.
Whether any of these applies to you depends on the cancer type, its stage, the biology of the tumour (receptor and molecular tests), your general health, and what you want treatment to achieve.
How a regimen is chosen
- Confirm the diagnosis and stage. A biopsy report identifies the cancer type and grade; scans and sometimes further tests establish the stage. Receptor and molecular tests (for example ER, PR and HER2 in breast cancer; EGFR, ALK and PD-L1 in lung cancer) can change the plan completely — sometimes away from chemotherapy altogether.
- Agree the goal. Cure, long-term control, or relief of symptoms. Saying the goal out loud changes the choice of drugs, the intensity, and how much side effect is reasonable to accept.
- Choose the regimen and schedule. Standard regimens come from clinical trials and national and international guidelines; the medical oncologist adapts them to your kidney and liver function, heart health, other illnesses and age. Most regimens are given in cycles — a treatment day or days followed by a rest period of one to four weeks so that normal tissue can recover.
- Review after every cycle. Blood counts, side effects and, at intervals, scans tell us whether to continue, reduce a dose, delay a cycle, or change course.
What to expect during treatment
Most chemotherapy is given as a drip through a vein in a day-care unit and you go home the same day; some drugs are tablets taken at home, and a few regimens need admission. A port or PICC line may be suggested if you will need many infusions.
Before each cycle, a blood test checks that your counts and organ function are safe to proceed. Anti-sickness medicines are given before and after the infusion, and you will be told exactly which tablets to take at home and when.
Common, expected effects include tiredness, nausea, changes in taste and appetite, mouth soreness, hair thinning or loss with some drugs, and a temporary drop in blood counts. Most are predictable and manageable, and most settle between cycles.
Side effects that need urgent attention
Chemotherapy lowers the white blood cells that fight infection, usually reaching their lowest point 7–14 days after a dose. An infection in that window can become serious quickly and the usual signs are muted. Contact the oncology team immediately, or go to the emergency department, if you have:
- a temperature of 38 °C (100.4 °F) or higher, or feel shivery and unwell even without a thermometer reading;
- bleeding or bruising that will not stop;
- vomiting or diarrhoea that stops you keeping fluids down for more than a day;
- breathlessness, chest pain, a new severe headache, or a swollen painful leg;
- a mouth so sore you cannot eat or drink.
Do not take paracetamol first to "see if it settles" — it can hide a fever that matters.
Questions worth asking at your consultation
- What is the goal of this chemotherapy for me — cure, control, or relief?
- Which tests were used to choose this regimen, and were receptor or molecular tests done?
- How will we know whether it is working, and when will we check?
- What side effects should I expect, and which ones mean I should call immediately?
- Are there alternatives — targeted therapy, immunotherapy, a clinical trial, or no treatment for now?
- How will treatment affect fertility, work, and daily life, and what support is available?
Preparing for your consultation
Bring the biopsy report, all scans with their written reports, any receptor or molecular test results, a list of current medicines (including supplements and alternative remedies), and a summary of other illnesses. If you have already started treatment elsewhere, bring the regimen name, dates and any side-effect notes. Bringing a family member helps — there is a lot to take in.
If you want an independent review of a plan you have already been given, see second opinion.