Cyclophosphamide (Cytoxan), or CTX, is a type of chemotherapy medicine called an alkylating agent. It is used to treat several types of cancer, including breast cancer.


How cyclophosphamide works

Cyclophosphamide attaches to and damages the DNA in cancer cells when they are in their resting phase (not dividing). After their DNA is damaged, the cells can’t keep dividing, and their growth slows or stops.


Who gets cyclophosphamide

Cyclophosphamide may be used in combination chemotherapy treatments for most types of invasive breast cancer, including triple-negative breast cancer. It can also be used with targeted therapy, such as trastuzumab (Herceptin), in treating HER2-positive breast cancers.

Other times cyclophosphamide can be used are

  • with the chemotherapy medicine doxorubicin (Adriamycin) after surgery as adjuvant treatment
  • as neoadjuvant (before surgery) treatment for breast cancers that require chemotherapy
  • in some cases to treat metastatic breast cancer

How cyclophosphamide is given

Cyclophosphamide is usually given along with other chemotherapy medicines. Combinations in breast cancer include:

Cyclophosphamide can be taken by mouth or 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 varies depending on the combination of medicines. Most breast cancer chemotherapy regimens are given every 2 or 3 weeks.

In some cases your doctor may recommend a dose-dense schedule, which means medicines are given with less time between treatments than in a standard chemotherapy treatment plan. For example, one common treatment is dose-dense doxorubicin (Adriamycin) and cyclophosphamide (Cytoxan) every 2 weeks for four cycles, followed by paclitaxel (Taxol) every 2 weeks for four cycles. An entire course of chemotherapy for breast cancer usually takes from 3 to 6 months.


Side effects and things to remember

Because cyclophosphamide affects normal cells as well as cancer cells, it can cause many different side effects including:

With cyclophosphamide, nausea and vomiting can be significant. Your doctor will give you anti-nausea medications with your chemotherapy. You should also be given medicines to take at home for nausea.

While you are taking cyclophosphamide, drink lots of fluids to avoid kidney and bladder side effects. Ask your doctor how much and how often you should drink each day. Call your doctor if you see blood in your urine.

Cyclophosphamide can cause long-term damage to the bone marrow. This means it can slightly increase your risk of developing leukemia, a blood cancer, when given in high doses.


Related resources


Stay connected

Sign up to receive emotional support, medical insight, personal stories, and more, delivered to your inbox weekly.


Reviewed and updated: August 31, 2015

Reviewed by: Laura M. Spring, MD


Was this page helpful?