Chemotherapy drugs treat cancer by disrupting the life cycle of cancer cells to destroy them and/or prevent them from growing or reproducing. Chemotherapy may be administered using a single drug, but more often it involves a combination of medications. Treatment with chemotherapy may be used before, after or concurrently with radiation therapy, surgery, biological therapy or bone marrow transplants.
Treatments can be administered in various ways. The type of chemotherapy medication used will largely determine the form of administration. For example, oral medications are given in pill or liquid form to swallow and topical medications are applied to the skin as creams, lotions or patches.
Other methods of chemotherapy administration can be some form of injection, in which a needle and syringe are used. Injected medications can be placed under the skin (subcutaneous), into muscles (intramuscular), into a body cavity (intracavity) or directly into a cancerous area (intralesional). However, most injected medications are delivered intravenously, that is, directly into a vein. Several types of vascular access devices (VADs) are used for are intravenous drug delivery. These include:
- Needle. Usually inserted into a vein in the hand or lower arm at the beginning of a treatment session, and removed at the end of the session.
- Catheter. Consists of a thin, flexible tube inserted into a larger vein, usually in the chest, arm, spine, abdomen, pelvis or chest. There are several types of catheters, including those that thread up towards the heart (peripherally inserted central catheter, or PICC) and those with several openings (tunneled central venous catheter, or TCVC). They may be used for long-term chemotherapy to minimize the number of needle sticks a patient must endure. They also may be used to administer several drugs at one time, or to administer drugs known to cause damage to skin and muscle tissue when they leak outside the vein.
- Port. In some cases, the catheter is attached to a small plastic or metal disc placed under the skin. This is called a port. External pumps or internal pumps (surgically implanted) are sometimes used to administer certain medications continuously.
Treatment sessions can be scheduled in a patient’s home, physician’s office, clinic, or at a hospital, either as an outpatient or as an inpatient.
In some cases, chemotherapy will be given in high doses to certain specific and restricted areas of the body. This is known as regional chemotherapy, and it is usually focused on the tumor-bearing area of the body. This allows for more of the medication to be concentrated in the cancerous region while minimizing side effects throughout the rest of the body. Examples of this type of chemotherapy include:
- Intra-arterial (artery)
- Intravesical (bladder)
- Intrapleural (chest)
- Intraperitoneal (abdomen)
- Intrathecal (central nervous system, via spinal fluid)
Different chemotherapy drugs work in different ways and at different points in the cell cycle. Using a combination of drugs in treatment can both increase the effectiveness of anti-cancer treatment and help prevent a cancer developing resistance to a single drug and sometimes can help minimize the side effects.
A medical oncologist (a physician who specializes in diagnosing and treating tumors) will decide which chemotherapy drugs to use based on several factors. These include:
- Cancer type and stage (how far it has spread)
- Patient’s age and health (including other diseases, such as liver or kidney diseases)
- Anti-cancer treatments given in the patient’s past
- Side effects associated with various anti-cancer medications
- Drug interactions among various anti-cancer medications and any other medications being taken by the patient
In all cases, weighing these factors can give physicians a better picture of which medication is best for a patient. Physicians also have to rely on their own judgment and clinical experience for the most effective treatment. As a result, different physicians may come to different conclusions about the details of the best approach to therapy.
Unlike most over-the-counter drugs, chemotherapy drugs have a very narrow therapeutic index. This means that chemotherapy drugs are only safe when used within strict guidelines – taking too little of a drug will produce little or no benefit, while taking too much of the drug can trigger potentially life-threatening side effects. For this reason, physicians very carefully calculate and measure the amount of chemotherapy medication that is delivered to a patient.
Chemotherapy is designed using two factors: dosage levels and chemotherapy cycles.
Dosages are usually measured in milligrams (mg), and appropriate levels may be based on a patient’s weight as expressed in kilograms (kg,1 kilogram equals 2.2 pounds). More often, the amount of a medication administered during an individual session is determined by a formula based on a patient’s body surface area (BSA). This is calculated based on a patient’s weight and height.
Chemotherapy session schedule
Chemotherapy sessions are scheduled at regular intervals known as cycles. Cycles are planned in a way that allows the drugs to effectively attack the cancer, while also providing time for normal cells to rest and recover from damage. However, the schedule used for specific patients with specific cancers varies greatly. Sessions may be held every other day or may be divided by weeks. In other cases, continuous administration over several consecutive days is the best approach. Each cancer and each cancer patient responds to chemotherapy drugs differently and different drugs may be used for different cancers. The sessions are adjusted according to the patient‘s recovery time and the tolerance for additional drugs. The characteristics of the drug(s) administered also affect the treatment schedule.