Fluorouracil is an antimetabolite chemotherapy medicine used to treat breast cancer. It is one of the most commonly used medicines to treat cancer. Fluorouracil is also known as 5-fluorouracil and 5-FU.

How fluorouracil works

Fluorouracil interferes with the normal growth process of cancer cells. It stops them from making and fixing DNA, the directions that cells use to grow. Fluorouracil causes the cells to die when they try to divide. It works at specific times in the growth of the cell.

Who gets fluorouracil

Fluorouracil may be used in chemotherapy treatment regimens for invasive breast cancer, including triple-negative breast cancer.

It can be used to treat any stage of breast cancer, including metastatic disease.

How fluorouracil is given

Fluorouracil is given with other chemotherapy medicines in breast cancer. Some common combinations in breast cancer include:

Fluorouracil is given by vein. It is usually given in several cycles, with a day (or days) of treatment followed by a period of “off” days. The exact schedule depends on the medicines used. Most chemotherapy regimens consist of between four and six cycles of treatment given over 3 to 6 months.

Side effects and things to remember

Side effects may include:

Before starting fluorouracil, tell your doctor about any medicines you are taking, including vitamins, herbal supplements and over-the-counter medicines. You should not take fluorouracil during the first trimester of pregnancy.

Your doctor will test your blood before and during treatment to check your white and red blood cell levels. Your liver and kidneys will also be checked.

Be sure to call your doctor right away if:

  • you have chest pain, as this may be a sign of heart problems
  • you have pain at the injection site, as this can be a sign of an allergic reaction
  • you have a high fever, as this can be a sign of a serious infection

Your doctor, pharmacist or nurse can help you manage your side effects. You can also go to our section on Side Effects for more information.



Reviewed and updated: August 31, 2015

Reviewed by: Adrienne Gropper Waks MD


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Living Beyond Breast Cancer is a national nonprofit organization that seeks to create a world that understands there is more than one way to have breast cancer. To fulfill its mission of providing trusted information and a community of support to those impacted by the disease, Living Beyond Breast Cancer offers on-demand emotional, practical, and evidence-based content. For over 30 years, the organization has remained committed to creating a culture of acceptance — where sharing the diversity of the lived experience of breast cancer fosters self-advocacy and hope. For more information, learn more about our programs and services.