What Is Chemotherapy?
Cancer chemotherapy is the use of chemical agents with ability to kill cancer (anticancer drugs) to treat cancer.
How does chemotherapy help?
Basic effect of chemotherapy drug is to kill the cancer cells by interfering at one or more points in their life cycle. The cancer cell during its multiplication has many chemical steps and a drug, depending on the chemical configuration can block one or few of them hence it is destroyed.
These drugs cannot differentiate between the cancer cell and a normal cell. They can kill any cell, which is multiplying rapidly. Hence normal cells that multiply rapidly in the body are also simultaneously destroyed. Some of these cells are the blood forming cells in the bone marrow, cells of the hair root (hair follicles), the soft layer covering our mouth and the entire gut (mucous membrane) and sperm forming cells. Their damage leads to side effects as decrease in the number of blood cells, fall of hair, ulcers in the mouth, decrease in the sperm count and so on. More about side effects will be discussed subsequently.
It has been long realised with chemotherapy drugs that higher the dose administered, higher the cell kill. That means a large dose can eliminate the cancer cells almost completely. But at the same time they will also damage the normal cells irreversibly. This cannot be accepted, as the normal systems have to be restored to have normal life. Hence the dose administered is usually such to eliminate a proportion of cancer cells while causing a reversible damage to normal cells. Most important normal cells to recover are bone marrow cells, which take about three weeks (rest period) for recovery. On recovery of the normal cells, next dose is administered to eliminate some more cancer cells. With each dose a proportion of cancer cells are eliminated and this can go on till all the cancer cells are eliminated. During this rest period the cancer cells also recover but slower than bone marrow cells, hence their growth is usually negligible. This forms the basis of so called ‘cycles’ or ‘pulses’ of the chemotherapy. The duration, frequency of cycles varies with the cancers, type of drugs used and other factors. By and large, six to eight cycles are administered at three weekly intervals.
All types of cancer cells cannot be killed by chemotherapy. While some are extremely sensitive to chemotherapy and can be eliminated completely, some are inherently resistant to it. Most are moderately sensitive and can be killed to a large extent. Such drug resistance can develop in a cancer during relapse.
There are many types of chemotherapy drugs; about sixty in number and more are being discovered. Each drug is useful in some type of cancer and has its own unique side effects. Usually, when cancer is treated with chemotherapy, a single drug is never used to treat cancer but several of them are used together. This is to ensure better cell-kill and to prevent emergence of drug resistance. Multiple drugs block the chemical path of the cell at several points to have a certain and better cell kill. Also such combination helps to prevent drug resistance (a mechanism to make the drug ineffective) a property that is inherent to cancer cell. Side effects are also taken into consideration while combining them. Use of multiple drugs to treat cancer is called ‘combination chemotherapy’.
What Can Chemotherapy Achieve?
Chemotherapy is used in several ways. After complete removal of the tumour, there is likelihood of invisible disease what is called as “micro-metastasis”. If not treated these cells will in due course of time grow in number and show up as metastasis. Hence it is advocated to give chemotherapy at this time itself to have the best chances of cure. This chemotherapy is called as ‘adjuvant chemotherapy’ and is attempted to cure the patient. Chemotherapy can also be used in large tumours that are considered inoperable by the surgeon. In such tumours the aim is to reduce the tumour size to an operable extent. Also, the same principle can be used for preservation of a limb in a tumour involving the lower or upper limb. Such chemotherapy administered before surgery with aim of decreasing the size is labelled as neo-adjuvant chemotherapy.
In some cases the chemotherapy is used for relief of symptoms produced by a large tumour and is known as palliative therapy. Such chemotherapy is intended to produce relief of the symptom and it may not be able to prolong the life of the patient.
Chemotherapy can be used along-with radiotherapy to add to each other’s effect. Some chemotherapy drugs in low doses can potentiate the effect of radiotherapy and this fact is used now to benefit the patients with cancer after surgery. This is referred to as ‘concurrent chemotherapy-radiotherapy’.
Thus, depending on the type of cancer and its stage of development, chemotherapy can cure a patient or give him additional life or simply improve his quality of life. The following can be the outcome of the chemotherapy.
- Kill all the cancer cells and lead to a cure (Curative therapy)
- Kill majority of the cells and relieve the symptoms thus improving the quality of life with some gain in survival.
- Kill some cells and keep other cells under check.
- Decreases the size of the tumour to make an inoperable tumour to an operable one.
- In some cancers it may not have any effect at all.
What chemotherapy shall I be getting?
You may have all the modalities or some of them. The sequence, the schedule of chemotherapy will depend on the type of and cancer, the condition of your heart, kidneys, liver, and blood counts. If you have received chemotherapy earlier, the earlier response, side effects will also be considered. Based on these your medical oncologist will decide the combination of drugs.
The dose, duration and frequency of chemotherapy will obviously depend on the type and stage of the tumour. Some tumours require long-term treatment while some require short-term chemotherapy. Mostly the chemotherapy cycles are repeated after three or four weeks. Some are to be given every day or week when combined with radiotherapy. When patient is on both radiotherapy and chemotherapy the sequence can also be varying with the type of cancer.
The most important thing for the patient is to follow the instructions carefully and to adhere to the schedule and timing of the chemotherapy. If the cycles are unduly delayed the cancer cells may grow in number and may adversely affect the result. Sometimes the delay due to side effects may become mandatory to avoid damage to normal tissues.
Where Will I Get Chemotherapy?
It is always advisable for chemotherapy to be administered in a hospital by an oncology nurse as “day-care’ or ‘in-patient’. It is also possible at home if it consists of simple oral medications. Some schedules require administration of lot of fluids in which case patient may have to be admitted for the duration of chemotherapy. This enables close observation by the staff and the oncologist to alter the dose the drugs depending on the side effects.
How Will I Get Chemotherapy?
Depending on the type of cancer you have and the drugs you are getting, your chemotherapy may be given in one or more of the following routes: an injection through a vein (intravenous IV), in the muscle (intra-muscular-IM), into the fat under the skin (subcutaneous- SC); or tablets of capsules by mouth. Some medicines may have to given into spinal fluid, peritoneal cavity or pleural space as the drug may not be able to reach in sufficient quantity when administered by any of the above manner.
Chemotherapy is most often given intravenously, when a thin needle is inserted into a vein on the hand or lower arm at the beginning of each treatment session and is removed at the end of the session. Usually the routes of IM and SC do not have any problem apart from pain of injection. By IV injections some problems encountered are damage of the veins, accidental leaking of the medicine from the vein while injecting causing large ulcers.
Sometimes, when chemotherapy has to be administered frequently and over a long period and there is an anticipated requirement of blood transfusions, antibiotics, fluids through veins, it would be painful and also difficult to get the veins repeatedly. In such patients, an alternative route could be established by means of long specialized tubes (catheter) of different types placed in one of the main veins in the chest. Some have open ends and others have a closed chamber that can be implanted under the skin over the chest. Through these catheters, chemotherapy can be delivered easily and blood samples can be drawn. More understanding of these catheters from the treating oncologists is advisable before going for them. Several types of pumps are available to make it easier administer chemotherapy over a long time so that patient can be ambulatory at home or hospital instead of being staying in the bed.