Chemotherapy, targeted therapy and immunotherapy: what is the difference?

When a doctor talks about “drug treatment”, you may hear several names: chemotherapy, targeted therapy, immunotherapy and hormone therapy. All of them are medicines and all work throughout the body, but each has its own way. This article explains the differences simply. Which one suits you is decided by your doctor after assessment.

Chemotherapy: the target is fast-dividing cells

Chemotherapy is one of the oldest drug treatments for cancer. These medicines target cells that grow and divide quickly. A cancer cell usually divides quickly, but healthy fast-dividing cells, such as hair roots, cells of the mouth and bone marrow, are affected too. For this reason mouth sores, hair loss, low blood counts and tiredness are common side effects.

Chemotherapy is usually given through a vein and sometimes by mouth. It is often given in courses (cycles), with a rest of a few weeks after each so the body can rebuild. Its aim can be to cure the disease, to lower the chance of it coming back, to slow its growth or to ease symptoms.

Targeted therapy: the target is specific proteins

Targeted therapy includes medicines that target specific proteins that control the growth and spread of a cancer cell. There are two common types: small-molecule tablets or capsules that act inside the cell, and monoclonal antibodies that attach to a target on the cell.

One important difference: targeted therapy is usually used when the tumour has that target. For this reason a test on a sample, called a “biomarker test”, often has to be done before treatment. In breast cancer, for example, the HER2 test result shows whether HER2-targeted medicines are suitable.

Its side effects differ from those of chemotherapy. The most common are diarrhoea and liver problems. High blood pressure, tiredness, mouth sores and skin problems also occur. Some side effects can be prevented with medicine. Over time a cancer cell may become resistant to the medicine.

Immunotherapy: the target is the immune system

Immunotherapy helps your own immune system recognise cancer cells and get rid of them. Its types include checkpoint inhibitors (a medicine that releases the natural brake of the immune system), monoclonal antibodies, treatment vaccines and cell transfer therapy. CAR T cell therapy is an example of cell transfer and is used in some blood diseases.

Because the immune system has become more active, it may also attack healthy tissues, so side effects may include inflammation in organs, diarrhoea, skin rashes and flu-like symptoms. Doctors and nurses cannot tell in advance which side effect will come and how severe it will be. So tell the team about every new change, and report new diarrhoea, a rash or shortness of breath right now.

Hormone therapy: for cancers that grow with hormones

Hormone therapy is for cancers that use hormones to grow, such as some breast and prostate cancers. This treatment blocks the making of the hormone or its effect. It is usually given as tablets or injections. Whether a breast cancer is “hormone receptor positive” is shown by a test on a sample of the tumour.

Side by side

• Chemotherapy: fast-dividing cells, cancerous or healthy
• Targeted therapy: specific proteins in the cancer cell; usually after a test on a sample
• Immunotherapy: strengthening the immune response against cancer
• Hormone therapy: blocking the effect of the hormone the cancer depends on

Why are they sometimes given together?

Many treatment plans are combined. Chemotherapy is “usually” given along with other methods such as surgery, radiation or targeted therapy. Chemotherapy can shrink a tumour before surgery or destroy remaining cells after it. Targeted therapy is also combined with chemotherapy or with other targeted medicines to reduce resistance. The doctor builds the combination on the type and stage of the disease, tests of the tumour and your condition.

A few questions you can ask

• Which type is my treatment, and why?
• What is the goal of this treatment?
• Is a test on my sample needed? What does the result say?
• Which side effects are common, and which mean I should call right now?
• Can I take supplements or herbal products? (Say so before taking them. Some supplements affect how the medicine works.)

Remember: many or few side effects are not a sign that the treatment is working or not. And if you get a fever of 38 degrees or higher in the middle of treatment, tell the team at once. This is an emergency.