Chemotherapy: The Basics

Author: OncoLink Team
Content Contributor: Joel W. Goldwein, MD 
Last Reviewed: February 21, 2020

What is chemotherapy?

Chemotherapy is a type of medicine that is used to treat cancer.

How does chemotherapy work?

Tumor cells, which make up cancer, grow and reproduce (multiply) very quickly. Normal, healthy cells know to stop reproducing and growing when they touch other cells. Cancer cells keep growing, not knowing when to stop. RNA and DNA in the cell tell it how to grow and reproduce. Chemotherapy hurts the RNA or DNA, which stops the cancer from growing.

What is the cell cycle?

The cell cycle is the way a cell copies itself to make more cells. This happens in phases:

  • Resting phase (GO; nothing is happening).
  • G1 phase (gap 1; a growth phase).
  • S phase (synthesis; the copying of DNA happens).
  • G2 phase (gap 2; one more growth phase).
  • M phase (mitosis; the division from 1 cell into 2).

How does chemotherapy affect the cell cycle?

Some chemotherapy medicines can kill a cell during any phase of the cell cycle. They are called cell-cycle nonspecific agents. Other chemotherapy medicines kill cancer cells only during a certain phase. They are also not able to work in the resting phase. These are called cell-cycle specific agents.

Cell-Cycle Nonspecific Chemotherapy Facts

  • Kill cancer cells at all phases of the cell cycle, including the resting phase.
  • These medicines work best when given in a “bolus dose.” A bolus dose is a large dose, given over a short period of time. For example, the dose may be given once over 20 minutes.
  • The cells don’t always die right away. A cell may have to go through several cycles of chemotherapy before it dies.
  • Repeat doses of chemotherapy may be given to continue to kill cancer cells.

Cell-Cycle Specific Chemotherapy Facts

  • These medicines are often given more than one time. This gives the chemotherapy the best chance to kill as many cells as possible.
  • They may be given in “divided doses” or given multiple times. For example, once a day for 5 days, or every 3 hours for 4 doses.
  • They can also be given as a nonstop infusion. This is an infusion that runs for several hours or more. Some chemotherapy infusions are given over several days.  

How is chemotherapy given?

Chemotherapy is called a “systemic” therapy. This means that it travels throughout the whole body to kill cells. Surgery and radiation are called “local” therapies because they treat only a certain part of the body. Chemotherapy can be given to a patient in a number of ways:

  • Orally (by mouth, in pill form).
  • Intravenously (IV, through a vein, either as a short infusion or continuously for one or more days).
  • As an injection or needle.
  • Directly into a body cavity (i.e.: the bladder, abdominal cavity).
  • Intra-arterially (into an artery) - used in special cases, such as limb perfusion treatment for melanoma.

When is chemotherapy given?

Your treatment may include more than one type of therapy (surgery, radiation, chemo, etc.). Common terms used to describe chemotherapy treatments:

  • Adjuvant Therapy: chemotherapy given after surgery to reduce the chance of your cancer coming back (recurrence).
  • Neo-adjuvant Therapy: chemotherapy given before surgery to shrink the tumor. This is to help the surgery be more successful.
  • Concurrent Therapy: when 2 or more therapies (radiation and chemo) are given together.

What is a regimen?

The regimen describes the combination of chemotherapies you will get. A combination is given because different chemotherapies can work well together. Regimens can be given “nicknames” based on the chemotherapies used in them. For example, the regimen called “CHOP” contains the medications Cytoxan, Hydroxydaunorubicin (also called Adriamycin), Oncovin, and Prednisone.

What is a cycle?

A cycle is the block of time in which a regimen is given. Each regimen can have a different cycle time. A cycle of CHOP is usually 21 days. This is how the cycle breaks down:

  • Cytoxan, adriamycin, and oncovin are given on day 1.
  • Prednisone is given on days 1-5.
  • You then have 16 days “off” without chemotherapy. This totals 21 days, making your cycle.
  • You then start all over again for a new cycle.

Your regimen and cycle will depend on what type of cancer you have and your treatment plan.

What is the goal of treatment with chemotherapy?

The goal of chemotherapy treatment depends on many issues. These can include what type of cancer you have, where it is, and any other medical problems you have. The goals of treatment can include:

  • Curing the cancer.
  • Stopping the cancer from going to other parts of the body.
  • Slowing the growth of the cancer.
  • Killing cancer cells in areas of metastases (other parts of the body that the cancer has spread to).
  • Ease symptoms that the cancer is causing to make you more comfortable (palliative).
  • The goals of chemotherapy also can change throughout treatment.

How do I know if chemotherapy is working for me?

There are several ways to find out if your treatment is working. These can include:

  • Radiology/Imaging Studies: CT scans, MRIs, PET scans.
  • Lab Draws: Your blood can be tested for tumor marker levels. Tumor markers are made by the tumor or by the body due to a tumor. If the level is lower, most likely the chemotherapy is working.
  • Checking Symptoms: If the symptoms caused by your cancer are getting better, then likely chemotherapy is working.

You will be closely followed while getting chemotherapy. It is important to check in with your care team regularly. Let them know of any changes in how you are feeling or any new side effects that you are having. 

Now that you have learned about how chemotherapy works, learn more about the specific medication you are taking.

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