Chemotherapy works by killing existing cancer cells and can help prevent the disease coming back.
There are many different types of chemotherapy, but the most common types are tablets and liquids that are put directly into the vein (intravenous chemotherapy).
Chemotherapy can be given before or after surgery, or on its own.
It can also be given in a palliative way, when the cancer has spread and chemotherapy is not being used to cure the disease, but it helps ease symptoms.
Chemotherapy can be used even when surgeons believe they have removed all the cancer, owing to the risk the disease might come back.
This can lower the risk of a cancer recurrence or a new cancer.
Professor Bob Phillips, Professor of Paediatric Oncology at the University of York, said: “For some types of cancers, chemotherapy can be given after to act to ‘mop up’ if there are any cancer cells left.
“The value of this varies between cancer types, and even the size and place of the same cancer type.”
Prof Andrew Beggs, Consultant Colorectal Surgeon at the Queen Elizabeth Hospital Birmingham, said preventive chemotherapy was “a bit like mopping a floor with bleach when you’ve spilt something on it, chemotherapy kills any spilt cells”.
Chemotherapy can also be combined with other treatments to make them more effective, such as when it is used alongside radiotherapy.
Chemotherapy given into a vein is usually carried out as an outpatient hospital procedure, whereas chemotherapy tablets can be taken at home, with regular check-ups from medical staff.
Sometimes, people have more than one type of chemotherapy.
How long they need treatment for also depends on the stage and type of cancer.
Prof Phillips said the timeframe for chemotherapy treatment was “hugely variable”, adding that it was given “traditionally between four and six ‘cycles’ (blocks) of chemo, each cycle lasting 21 days and consisting of a day or few days of chemo.”
He added there would then be “time for the body to recover from it, while the chemo keeps damaging the cancer cell.
“There are also some which are daily, some which are four-weekly, and some which are two-weekly.”
Side-effects of chemotherapy occur because healthy cells are damaged alongside any cancer cells.
Treatment can therefore make people feel very tired and nauseous, and cause them to vomit and lose their hair.
People undergoing chemotherapy are also at an increased risk of getting infections, a sore mouth, dry, sore or itchy skin and bowel issues.
Sometimes, other medicines are given to patients to help with these side-effects.
More than 375,000 people are diagnosed with cancer each year in the UK and there are more than 167,000 deaths from the disease.
Half of people with cancer survive for a decade or longer after diagnosis.
Cancer survival depends on the cancer type and whether the disease is caught early.
Breast cancer is the most common cancer in the UK, followed by prostate cancer, lung cancer and bowel cancer.
Asked whether age was a factor in survival rates and the success of chemotherapy treatment, Prof Phillips said: “Sort of, but not in a simple way. Generally speaking, the healthier someone is before cancer treatment, the closer-to-optimal the amount of chemo and the gaps-between-chemo can be. Generally, the younger someone is the healthier they will be.”
Prof Beggs said: “Young onset cancer is by no means rare. I run a clinic for early-onset cancer in adults and we are seeing more and more people in their 40s with cancer.”
He went on: “Age has no effect on the success rate of chemotherapy except when the cancers are ‘immune hot’ which are commoner in young people – in this case a type of chemotherapy called immunotherapy could be given.
“Young people also better tolerate higher doses of chemotherapy and so can be given stronger regimens that are more likely to kill any left over cells.”