Cancer treatment explained: chemotherapy and radiotherapy

How chemotherapy works

Chemotherapy uses medicines that attack cancer cells, most often by targeting cells that are dividing rapidly, which is a hallmark of cancer. Because the medicines travel through the bloodstream, chemotherapy is a "systemic" treatment, able to reach cancer cells throughout the body — useful when cancer has spread or might have spread beyond one spot. It is usually given in cycles, with treatment followed by a rest period that lets the body recover before the next round. Chemotherapy can be given through a drip into a vein, as tablets, or occasionally by other routes. Many different drugs exist, often used in combinations chosen for the specific type of cancer. Treatment plans are tailored by specialists to balance effectiveness against side effects.

How radiotherapy works

Radiotherapy uses high-energy radiation, similar to a very focused X-ray, to damage the DNA inside cancer cells so they can no longer grow and divide. Unlike chemotherapy, it is usually a "local" treatment, precisely aimed at the tumour and a small margin around it, sparing as much healthy tissue as possible. Most commonly it is delivered from a machine outside the body (external beam radiotherapy), often in short daily sessions over several weeks, each lasting only minutes and completely painless. Sometimes radiation is placed inside the body close to the tumour, a technique called brachytherapy. Modern radiotherapy is remarkably precise, using detailed scans and computer planning to shape the radiation beams and protect nearby healthy organs as much as possible.

Why treatments are combined

Cancer treatment is rarely one thing alone; specialists often combine approaches to give the best chance of success. Chemotherapy or radiotherapy may be used before surgery to shrink a tumour and make it easier to remove, or afterwards to destroy any remaining cancer cells and reduce the risk of it returning. The two can also be given together, as chemoradiotherapy, when the drugs make cancer cells more sensitive to radiation. The aim of treatment varies: it may be curative, intended to get rid of the cancer completely, or palliative, focused on controlling the cancer, easing symptoms, and improving quality of life when a cure is not possible. Decisions are made by a multidisciplinary team of specialists, always in discussion with the patient.

Understanding side effects

Both treatments can cause side effects because they also affect some healthy cells, though modern techniques and supportive care have reduced these considerably. Chemotherapy, acting throughout the body, can cause tiredness, nausea, hair loss, a higher risk of infection because it lowers the number of infection-fighting blood cells, and mouth soreness — though exactly which effects occur depends on the drugs used. Radiotherapy side effects are usually limited to the treated area, such as skin becoming sore or red, tiredness, and effects specific to the part of the body being treated. Most side effects are temporary and improve after treatment ends, and teams provide medicines and advice to prevent or ease them. Importantly, a lowered immune system during chemotherapy means infections must be taken very seriously.

Support, newer treatments and looking ahead

Cancer care today extends far beyond chemotherapy and radiotherapy. Newer treatments include targeted therapies, which home in on specific weaknesses in cancer cells, and immunotherapy, which helps the body's own immune system recognise and attack cancer. These may be used alongside or instead of traditional treatments, depending on the cancer. Throughout treatment, patients are supported by specialist cancer nurses, and help is available for managing symptoms, emotional wellbeing, nutrition, and practical concerns. It is important to keep in close contact with your team and to report new or worsening symptoms promptly. If you are having chemotherapy and develop signs of infection such as a high temperature, contact your team's emergency line straight away — this can be a medical emergency needing urgent treatment.