Chemo, in short, stands for chemical and therapy means treatment. Chemotherapy, therefore, is defined as the treatment of cancer with chemicals (drugs). It is an aggressive therapy that destroys the rapidly multiplying cancer cells in the body. Doctors often refer to it as “chemo”, in short.

It usually works by preventing the cancer cells from growing and multiplying. Chemo also affects the growing normal cells but since cancer cells grow and divide much faster than normal cells, chemotherapy’s effect on the cancer cells is much more pronounced.

Chemo is given either by admitting the patient to a hospital if required or can be given to an outdoor patient (non-admitted patient) who will then be sent home after the doctor has satisfied himself with the absence of any possible side effects.

Doctors may prescribe it to a cancer patient alone or in conjunction with other treatments, such as radiation therapy, or biologic therapy, or before or/and after cancer surgery.

Chemotherapy does have side effects. Some chemo drugs can be quite painful. Painful side effects, such as muscle and joint pains, headaches, and stomach pains are seen and can last for a long time even after the treatment ends.

How does chemotherapy work?

The chemotherapy drug circulates throughout your body through the bloodstream. It can, therefore, act on cancer cells anywhere in the body. That is why it is called systemic treatment.

The chemo drugs target cells that grow and divide rapidly, as cancer cells do, and stop them from growing. They do this by interfering with cell division; by destroying the proteins involved in cell division or by specifically destroying the DNA of fast-growing cells in the body.

DNA (deoxyribonucleic acid) is a complex molecule inside the cell that controls the function and behavior of the cell. The chemotherapy drugs act on it and kill cancer cells during all phases of the cell cycle, including the resting phase.

However, these drugs can also damage some fast-growing normal healthy cells, especially those of the skin, hair, intestines, and bone marrow. It is this damage to normal cells, which causes side effects like hair loss and a feeling of sickness. Normal cells, however, do repair their DNA damage while cancer cells cannot. That is one of the major differences between the normal cell and the cancer cell.

What does chemotherapy do? Purpose

Combination chemotherapy of two or more drugs is usually given for better results. What are the results that are obtained? Chemo can:

  • Give relief from cancer symptoms.
  • Slow down the growth of cancer and prevent its metastasis
  • Kill all cancer cells in the body including those that have spread.
  • Work in conjunction with other forms of cancer treatments to enhance their effectiveness for better results.
  • Sometimes, doctors administer chemotherapy drugs before cancer surgery or cancer radiation to shrink the tumor. This is called neoadjuvant chemotherapy.
  • At times, chemo is given after surgery or radiation to kill any remaining cancer cells. This is called adjuvant chemotherapy.
  • In some cases, it is given to reduce the severity of the cancer symptoms. It is not given as a curing agent. This is called palliative chemotherapy.

Choosing a chemotherapy drug

Research has helped to establish specific protocols that include the types of drugs, their doses, and their schedule. Each protocol that is finalized is based on the type of cancer, stage of cancer, and other characteristics of the person’s cancer. This helps the doctor in selecting the right chemotherapy drug or a combination of drugs for a particular case.

Chemotherapy has its side effects. Utmost care is exercised in people who are old and frail or who have other medical complications because they may not be able to tolerate certain chemotherapy protocols. Even healthy individuals have to be weighed with caution before deciding on the chemo protocol.

The possible risks involved and the potential benefits must be carefully weighed before deciding on the treatment. The doctors may choose a single drug rather than an approved combination of drugs to minimize the risks.

Sometimes, at the patient’s request, the doctor may decide not to use this form of therapy but focus on maintaining the quality of life of the patient with supportive care.

So, what does the doctor look for in finalizing the chemo drug for a particular case? There are close to a hundred chemotherapy drugs. The doctor’s choice of a cancer drug and its dosage depends on the following factors:

  • The general condition of the patient including age
  • Presence of any other illness such as diabetes, hypertension, heart disease
  • Type of cancer present
  • Stage of cancer when detected
  • Whether it is first-time cancer or a recurring cancer
  • Besides the choice of the right cancer drug, choosing the right dosage is important for the best results. Here the skill and experience of your cancer specialist play an important part.

Nevertheless, it is impossible to predict how beneficial the therapy will be for any individual. The response to a particular therapy can be either complete or partial.

However, the response rates have improved dramatically over the years and research has continuously developed new drugs to bring about improved outcomes and better survival rates.

Routes of Administration: How are chemotherapy drugs given to the patient?

Chemotherapy is mostly administered intravenously but it can also be given in the following ways:

  • Orally, in the form of pills, capsules, or liquids
  • By injection through the intramuscular route
  • Through the arterial route
  • By injection through the intravenous route
  • By injection into the peritoneum ( membrane cavity covering the abdomen)
  • Chemo drugs are also available for topical application on the skin

Chemotherapy doses are administered after sufficient intervals in order to allow the healthy cells that have been damaged, to repair or recover.

Chemotherapy doses: Duration and frequency

A chemotherapy dose or session varies in duration and frequency and depends on the individual treatment protocol, which your doctor plans and prescribes. For some, it may last for three or four hours, while for others it may last for only half-hour.

You may need four to eight cycles of chemotherapy to finish a “course” and treat your cancer. Your course can last 3 to 6 months to complete. Moreover, you may require more than one course of chemo cycles to beat your cancer.

To better understand this: Each 3-week period is called a treatment cycle. A number of cycles make up a course of chemotherapy. A course usually lasts 3 months to 6 months.

However, there may be a change in your cycles if your doctor feels so, after evaluating the effects of the drug.

The chemotherapy drug stays in the body for 2 -3 days. Most patients experience short-term and long-term side effects. It is necessary, therefore, that you be accompanied when you go for a chemo session. Never drive the vehicle yourself back, after a session. Take that day and the day after, off from work and take rest.

Chemotherapy drugs: Types, how they act, and examples

Chemotherapy drugs are divided into different groups depending on their mode of action, their chemical structure, and their interaction with other drugs.

1. Alkylating Agents

Alkylating drugs are the oldest drugs being used even today in different types of cancers. These agents act directly on the DNA of the cell and stop the cancer cells from reproducing.

They are effective in killing the cells in all phases of the cell cycle. Examples of alkylating agents include  Chlorambucil, Cyclophosphamide, Cisplatin, and Carboplatin.

2. Antimetabolites

Antimetabolites are called “cytotoxic” drugs because they kill cells. They act by mimicking the molecules that a cell needs to grow. The cancer cells are tricked into taking in the drugs and then using them instead of their genetic material: RNA and DNA.

Antimetabolites interfere with DNA and RNA growth thereby preventing mitosis (cell division). Examples are Methotrexate, Fluorouracil, and Fludarabine.

3. Anti-tumor antibiotics

Anti-tumor antibiotics are chemotherapeutic agents that block the action of the enzymes, which interfere with DNA replication. They act by either breaking up the DNA strands or slowing down and stopping the DNA and RNA synthesis that cells need to grow. Their action lasts during all phases of the cell cycle.

They are used in a variety of cancers but because of their cardiotoxicity, their doses are often limited. Examples are Bleomycin, Doxorubicin, and Mitoxantrone.

4. Topoisomerase inhibitors

Topoisomerase is an enzyme that plays an important role in cellular replication and the functioning of DNA. Topoisomerase inhibitors are chemical compounds that interfere with the function of the enzyme topoisomerase and thereby inhibit the duplication of DNA leading to cell death through apoptosis.

Examples include irinotecan and topotecan.

5. Mitotic inhibitors

These are plant-based compounds. They stop mitosis by inhibiting enzymes, which are responsible for cell reproduction.

They prevent cells from dividing and forming new cells and can damage cells in all phases by keeping enzymes from making proteins needed for cell reproduction.

Examples of mitotic inhibitors that are often used in the treatment of cancer include paclitaxel, docetaxel, vinblastine, vincristine, and vinorelbine.

6. Corticosteroids

Steroids help to reduce inflammation and thereby manage pain. They are sometimes part of the primary cancer treatment itself in some lymphomas and multiple myeloma.

In some cases, they are also used along with other chemotherapy drugs and also to control the side effects of nausea and vomiting. Know more about the uses of steroids for treating cancer.

Examples of steroids used in cancer treatment include:

  • prednisolone
  • methylprednisolone
  • dexamethasone
  • hydrocortisone