Overview on chemotherapy:
Chemotherapy, or ‘chemo’, is the most common form of cancer treatment. Chemo uses drugs called cytotoxics to kill or slow the growth of cancer cells.
While chemotherapy drugs can stop cancer cells growing and multiplying, they also affect normal, healthy cells in the process.
That’s why fast growing cells such as the ones in your hair and inside your mouth are damaged by chemotherapy.
The most effective way of killing cancer through chemotherapy is by using a number of different drugs rather than relying on one.
Each period of chemotherapy treatment is called a cycle. After each cycle there is usually a rest period, so that normal cells repair themselves and the body begins to regain its strength.
Chemotherapy is an aggressive drug treatment that reduces rapidly growing cells such as cancer cells. Chemotherapy is considered a systemic treatment, which means it affects the entire body. Chemotherapy may be combined with other treatments such as hormone therapy or radiation.
How Is Chemotherapy Given?
Chemotherapy drugs can be given in a variety of different ways.
The method of administration of chemo treatments along with the dose is determined by rigorous testing called clinical trials, which are done prior to the specific chemo drug being available for commercial use with patients. During this testing process, scientists and doctors determine how specific chemo drugs are absorbed in the body and how they work. Sometimes stomach juices can destroy different chemicals, making some medications impossible to give as a pill. Other substances are found to have better anti-cancer action if given intravenously (needle in the vein). Some medications can be given as an injection into the muscle and still others are absorbed when given directly into the bladder or the abdominal cavity.
Why Chemotherapy Is Used?
Chemotherapy is primarily used to:
- lower the total number of cancer cells in your body
- reduce the likelihood of cancer spreading
- shrink tumor size
- reduce current symptoms
If you’ve undergone surgery to remove a cancerous tumor, such as a lumpectomy for breast cancer, your oncologist may recommend that you have chemotherapy to ensure that any lingering cancer cells are killed as well.
Chemotherapy is also used to prepare you for other treatments. It could be used 
to shrink a tumor so it can be surgically removed or to prepare you for radiation therapy.
In the case of late-stage cancer, chemotherapy may help relieve pain.
Besides treatment for cancer, chemotherapy may be used to prepare people with bone marrow diseases for a bone marrow stem cell treatment and it may be used for immune system disorders.
How Does Chemotherapy Work?
Normally, cells live, grow and die in a predictable way. Cancer occurs when certain cells in the body keep dividing and forming more cells without the ability to stop this process. Chemotherapy protocols involve destroying cancer cells by keeping the cells from further multiplying. Unfortunately, in the process of undergoing chemotherapy protocols, healthy cells can also be affected, especially those that naturally should divide quickly.
Chemotherapy protocols strive to maximize the elimination of cancer cells while minimizing the negative effects that these protocols have on healthy cells.
How Do Doctors Decide Which Chemotherapy Drugs To Give?
The types of chemotherapy drugs are selected based on a variety of information and factors:
Research: Chemotherapy was first introduced in the 1940’s. For the next 20 years, it was considered an investigational treatment. In the last 30 years, chemotherapy information evolved and many more effective drugs have been developed. During all of this time, doctors have documented responses and conducted clinical trials comparing standard treatments to new treatments. This process of gathering chemotherapy information has helped to establish specific protocols (types of drugs, doses of drugs and schedule of drugs) based on the type of cancer, stage of cancer, and other specifics about a person’s cancer. Currently, most types of cancer have some standard protocols that help guide the doctors in selecting the right chemotherapy for an individual with cancer.
Response rates: In evaluating chemotherapy information and choosing a protocol for a given patient, doctors will consider the response rate of the particular type and stage of cancer to the proposed drug or drugs. Response rates refer to the number of people whose tumours will respond (shrink or disappear) to the drug or drugs given. Response rates are established through research. For example, a certain type and stage of cancer might have a 70% response rate to a certain combination of drugs.
The Health of the Patient: Chemotherapy has toxicities. It must be given with care – even to healthy individuals. People who are extremely old and frail or who have other medical complications may not be able to tolerate certain chemotherapy protocols. In these cases, the potential risks versus benefits must be discussed before deciding on the treatment. In some cases, the doctors may suggest a single drug rather than a “standard combination” of drugs. In other cases, the doctor and patient may decide not to pursue chemotherapy and, instead, focus on quality of life.
How Long is Chemotherapy Given?
The length of chemotherapy treatment is determined by a variety of factors. These include the type of cancer, the extent of cancer, the types of drugs that are given, as well as the expected toxicities of the drugs and the amount of time necessary to recover from these toxicities.
Duration of the Cycle
Chemotherapy treatment may be a single drug or a combination of drugs. The drugs may all be given on a single day, several consecutive days, or continuously as an outpatient or as an inpatient. Treatment could last minutes, hours, or days, depending on the specific protocol.
Frequency of the Cycle
Chemotherapy may repeat weekly, bi-weekly, or monthly. Usually, a cycle is defined in monthly intervals. For example, two bi-weekly chemotherapy sessions may be classified as one cycle.
Number of Cycles
In most cases, the number of cycles – or the length of chemotherapy from start to finish – has been determined by research and clinical trials.
When cure is the treatment goal. Adjuvant chemotherapy (therapy after surgery has removed all visible cancer) may last 4-6 months. Adjuvant chemotherapy is common in cancers of the breast and colon. In cancers of the testis, Hodgkin and non-Hodgkin lymphoma, and leukemias, length of chemotherapy treatment may be up to a year.
When there is visible disease, the length of chemotherapy treatment will depend upon the response of the disease to therapy. If the disease disappears completely, chemotherapy may continue for 1-2 cycles beyond this observation to maximize the chance of having attacked all microscopic disease.
If the disease shrinks but does not disappear, chemotherapy will continue as long as it is tolerated and the disease does not grow.
If the disease grows, the chemotherapy will be stopped. Depending on the health and wishes of the patient, either different drugs will be given to try to kill the cancer, or chemotherapy will be stopped and the goal changed to focus on patient comfort
How Can We Tell if Chemotherapy is Working?
With the exception of adjuvant chemotherapy, in which there is no apparent cancer present, the effectiveness of chemotherapy on cancer cells is measured in terms of “response.” The techniques to monitor responses can be similar to the tests used to diagnose cancer.
A lump or tumour involving some lymph nodes can be felt and measured externally by physical examination
Some internal cancer tumors will show up on an x-ray or CT scan and can be measured with a ruler
Blood tests, including those that measure organ function can be performed.
A tumor marker test can be done for certain cancers
Regardless of the test used – whether blood test, cell count, or tumor marker test, it is repeated at specific intervals so that the results can be compared to earlier tests of the same type.
What Is Chemotherapy Resistance?
Chemotherapy resistance occurs when cancers that have been responding to a therapy suddenly begin to grow. In other words, the cancer cells are resisting the effects of the chemotherapy. You may hear statements like the “cancer chemotherapy failed.” When this occurs, the drugs will need to be changed.
There are several possible reasons for chemotherapy resistance:
- Some of the cells that are not killed by the chemotherapy mutate (change) and become resistant to the drug. Once they multiply, there may be more resistant cells than cells that are sensitive to the chemotherapy.
- Gene amplification. A cancer cell may produce hundreds of copies of a particular gene. This gene triggers an overproduction of protein that renders the anticancer drug ineffective.
- Cancer cells may pump the drug out of the cell as fast as it is going in using a molecule called p-glycoprotein.
- Cancer cells may stop taking in the drugs because the protein that transports the drug across the cell wall stops working.
- The cancer cells may learn how to repair the DNA breaks caused by some anti-cancer drugs.
- Cancer cells may develop a mechanism that inactivates the drug.
- Research is underway to investigate ways of reducing or preventing chemotherapy resistance.