How is Chemotherapy Used to Treat Cancer?
Chemotherapy is the use of any drug to treat any disease. But to most people, the word chemotherapy means drugs used for cancer treatment. It’s often shortened to “chemo.”
Surgery and radiation therapy remove, kill, or damage cancer cells in a certain area, but chemo can work throughout the whole body. This means chemo can kill cancer cells that have spread (metastasized) to parts of the body far away from the original (primary) tumor.
Goals of chemotherapy treatment
If your doctor has recommended chemotherapy to treat your cancer, it’s important to understand the goals of treatment when making treatment decisions. There are three main goals for chemotherapy (chemo) in cancer treatment:
If possible, chemo is used to cure cancer, meaning that the cancer is destroyed – it goes away and doesn’t come back.
Most doctors don’t use the word “cure” except as a possibility or intention. So, when giving treatment that has a chance of curing a person’s cancer, the doctor may describe it as treatment with curative intent.
There are no guarantees, and though cure may be the goal, it doesn’t always work out that way. It often takes many years to know if a person’s cancer is really cured.
If cure is not possible, the goal may be to control the disease. Chemo is used to shrink tumors and/or stop the cancer from growing and spreading. This can help the person with cancer feel better and live longer.
In many cases, the cancer doesn’t completely go away, but is controlled and managed as a chronic disease, much like heart disease or diabetes. In other cases, the cancer may even seem to have gone away for a while, but it’s expected to come back. Then chemo can be given again.
Chemo can also be used to ease symptoms caused by the cancer. This is called palliative chemotherapy or palliation.
When the cancer is at an advanced stage, meaning it’s not under control and has spread from where it started to other parts of the body, the goal may be to improve the quality of life or help the person feel better. For instance, chemo may be used to help shrink a tumor that’s causing pain or pressure.
It’s important to know that any treatment that’s used to reduce symptoms or improve comfort is called palliative care. For example, anti-nausea treatments or pain medicines are palliative, and can be used at all stages of treatment. It can be confusing when chemo is used as a palliative treatment, because it’s most often used to try to cure or control the cancer. But when it’s used with the goal of comfort, chemo becomes palliative care.
Planning chemotherapy treatments
You and your cancer doctor, called an oncologist, will decide what drug or combination of drugs you will get. Your doctor will choose the doses, how the drugs will be given, and how often and how long you’ll get treatment. All of these decisions will depend on the type of cancer, where it is, how big it is, and how it affects your normal body functions and overall health.
Cancer can be treated with a single chemo drug, but often several drugs are used in a certain order or in certain combinations (called combination chemotherapy). Different drugs that work in different ways can work together to kill more cancer cells. This can also help lower the chance that the cancer may become resistant to any one chemo drug.
Sometimes chemo is the only treatment you need. More often, chemo is used with surgery or radiation therapy or both. Here’s why:
- Chemo may be used to shrink a tumor before surgery or radiation therapy. Chemo used in this way is called neoadjuvant therapy.
- It may be used after surgery or radiation therapy to help kill any remaining cancer cells. Chemo used in this way is called adjuvant therapy.
- It may be used with other treatments if your cancer comes back.
Determining which chemotherapy drugs to use
In some cases, the best choice of doses and schedules for each chemo drug is clear, and most doctors would recommend the same treatment. In other cases, less may be known about the single best way to treat people with certain types and stages of cancer. In these cases, different doctors might choose different drug combinations with different schedules.
Factors to consider when choosing which drugs to use include:
- The type of cancer
- The stage of the cancer (how far it has spread)
- The patient’s age
- The patient’s overall health
- Other serious health problems (such as heart, liver, or kidney diseases)
- Types of cancer treatments given in the past
Doctors take these factors into account, along with information published in medical journals and textbooks describing the outcomes of similar patients treated with chemo.
Determining chemotherapy doses
Most chemotherapy (chemo) drugs are strong medicines that have a fairly narrow range for dose safety and effectiveness. Taking too little of a drug will not treat the cancer well and taking too much may cause life-threatening side effects. For this reason, doctors must calculate chemo doses very precisely.
Depending on the drug(s) to be given, there are different ways to determine chemo doses. Most chemo drugs are measured in milligrams (mg).
The overall dose may be based on a person’s body weight in kilograms (1 kilogram is 2.2 pounds). For instance, if the standard dose of a drug is 10 milligrams per kilogram (10 mg/kg), a person weighing 110 pounds (50 kilograms) would get 500 mg (10 mg/kg x 50 kg).
Some chemo doses are determined based on body surface area (BSA), which are calculated using height and weight. BSA is expressed in meters squared (m2).
Because children’s bodies process drugs differently, dosages for children and adults differ, even after BSA is taken into account. Children may have different levels of sensitivity to the drugs, too. For the same reasons, dosages of some drugs may also be adjusted for people who:
- Are elderly
- Have poor nutritional status
- Are obese
- Have already taken or are currently taking other medicines
- Have already had or are currently getting radiation therapy
- Have low blood cell counts
- Have liver or kidney diseases
Determining a chemotherapy schedule (cycle)
Chemotherapy is commonly given at regular intervals called cycles. A cycle may be a dose of one or more drugs followed by several days or weeks without treatment. This gives normal cells time to recover from drug side effects. Sometimes, doses may be given a certain number of days in a row, or every other day for several days, followed by a period of rest. Some drugs work best when given continuously over a set number of days.
Each drug is given on a schedule that makes the most of its anti-cancer actions and minimizes side effects. If more than one drug is used, the treatment plan will say how often and exactly when each drug should be given. The number of cycles given may be decided before treatment starts, based on the type and stage of cancer. In some cases, the number is flexible, and will take into account how the treatment affects the cancer and the person’s overall health.
Changing chemotherapy doses and schedules
In most cases, the most effective doses and schedules of drugs to treat specific cancers have been found by testing them in clinical trials. It’s important, when possible, to get the full course of chemo, the full dose, and keep the cycles on schedule. This gives a person the best chance of getting the maximum benefit from treatment.
There may be times, though, when serious side effects require adjusting the chemo plan (dose and/or schedule) to allow you time to recover. Sometimes, you might be given supportive medicines to help your body recover more quickly. Again, the key is to give enough chemo to kill the cancer cells without causing other serious problems.
Fuchs-Tarlovsky V. Role of antioxidants in cancer therapy. Nutrition. 2013;29(1):15-21.
Last Medical Review: February 11, 2016 Last Revised: February 16, 2016