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What  is  chemotherapy  and  why  might  I  need  it?

Chemotherapy is a drug treatment that destroys cancer cells. There are many different types of chemotherapy drugs that work in various ways. These can be used as single treatments or in combination.

How does chemotherapy work?

To understand how chemotherapy ​​​​​​​ works, it may help to know that normal cells grow and divide in a cycle. This happens in all cells and is happening all the time. The cell cycle is normally tightly controlled; however, this regulation may be lost in cells that are cancerous, leading to rapid cell division and uncontrolled growth.​​​​​​​

Chemotherapy targets rapidly dividing cells

Chemotherapy ​​​​​​​ destroys cancer cells at certain points during the cell cycle.

  • some chemotherapy drugs damage cells before they divide when the cell content is being copied
  • some chemotherapy drugs damage cells when the cells are dividing

Chemotherapy targets cells that are rapidly dividing. This means that the effects of chemotherapy are focused on cancer cells but can also affect other rapidly dividing cells such as those involved with hair growth. Chemotherapy can therefore also cause some damage to normal tissues.
These drugs can also move through the bloodstream to other parts of the body, so damage can be caused to tissues in areas other than the location of the primary and secondary tumours ​​​​​​​ such as cells in your blood, mouth and digestive system.

Types of chemotherapy treatment

There are many different types of chemotherapy used in the treatment of metastatic breast cancer . These treatments all target rapidly dividing cells.

The type of chemotherapy you receive may depend on the type of your breast cancer. Some of the most frequently used chemotherapies are listed below:

Type of treatment Action
Alkylating agents Cause breaks in DNA ​​​​​​​ , preventing replication
Anti-tumour antibiotics Block the formation of DNA and RNA, preventing replication
Plant derivatives Block part of the cell cycle, preventing cells dividing and replicating
Antimetabolites Block the formation of DNA and RNA, preventing replication

If you have received treatment for early breast cancer, your doctor may have to modify which chemotherapy you receive for metastatic breast cancer. This chemotherapy regimen might also be different from what you received in early breast cancer.

Your doctor will discuss with you the different chemotherapy options that are available.

How is chemotherapy given?

Most chemotherapy ​​​​​​​ treatments such as alkylating agents, anti-tumour antibiotics, plant derivatives and some antimetabolites are given intravenously at the hospital. This means they are given directly into a vein .

​​​​​​​These types of chemotherapy are given in cycles. A cycle can vary from once a week to once every three or four weeks and each treatment cycle is followed by a period of recovery. The number of cycles you receive, and the length of time in between cycles, will vary dependent on the type of treatment. Your doctor will discuss this with you.

A few chemotherapy treatments including some antimetabolites can be taken orally as a tablet or capsule. These treatments are also given in a cycle. Your doctor will discuss with you how your treatment should be taken and the length of time you may be on the treatment for.
If chemotherapy is an option for you, your doctor will discuss how and when you receive treatment.
​​​​​​​Some chemotherapy treatments are given in combination with another treatment such as targeted therapy ​​​​​​​, or another type of chemotherapy. Your doctor will discuss what combination of treatments might be suitable for you.

What are the side effects?

Chemotherapy can cause side effects. These will vary from person to person and will depend on the specific chemotherapy ​​​​​​​ treatment or combination of chemotherapy treatments. Talk to your doctor about the potential side effects of chemotherapy and the treatments that may be the best option for you.

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The What’s Breast for Me? Campaign is funded by Pfizer Healthcare Ireland. Copyright © 2024 Pfizer Healthcare Ireland. All rights reserved. This site is intended for residents of the Republic of Ireland. The information provided on this site is intended for general information and education and is not intended to be a substitute for advice provided by a doctor or other qualified healthcare professional. All decisions regarding patient care must be made with a healthcare provider, considering the unique characteristics of the patients.


Date of preparation: January 2024