Cyclophosphamide
- Medical Review: Madeline Miceli, MD
Cyclophosphamide (Cytoxan) is a type of chemotherapy medicine used to treat early-stage and metastatic breast cancer.
It belongs to a group of chemotherapy medicines called alkylating agents.
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 chemotherapy regimens for most types of early-stage invasive breast cancer, such as hormone receptor-positive breast cancer and triple-negative breast cancer. It can also be used with targeted therapy, such as trastuzumab (Herceptin), to treat HER2-positive breast cancers.
In early-stage breast cancer, cyclophosphamide can be given before surgery (neoadjuvant treatment) or after surgery (adjuvant treatment).
Cyclophosphamide is also sometimes given to treat metastatic breast cancer.
How cyclophosphamide is given
Cyclophosphamide is usually given along with other chemotherapy medicines. Combinations in breast cancer include:
- AC (Adriamycin and Cyclophosphamide)
- AC-T (AC followed by Taxol)
- TC (Taxotere and Cyclophosphamide)
- CAF (Cyclophosphamide, Adriamycin and Fluorouracil)
- TAC (Taxotere, Adriamycin and Cyclophosphamide)
- CMF (Cyclophosphamide, Methotrexate, and Fluorouracil)
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:
- Nausea and vomiting
- Loss of appetite
- Diarrhea
- Hair loss or thinning
- Mouth sores
- Weight loss
- Menstrual cycle changes
- Nail and skin changes
- Decrease of white blood cells, red blood cells and platelets
- Taste changes
- Bladder irritation
- Nasal congestion
Cyclophosphamide can cause decreased blood counts. Your doctor will order blood tests regularly to monitor your blood counts.
With cyclophosphamide, nausea and vomiting can be significant. Your doctor will give you anti-nausea medications with your chemotherapy. Your care team will also prescribe medicines to take at home for nausea.
While you are taking cyclophosphamide, drink plenty 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 over time.
Visit our section on side effects for more information.
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Reviewed and updated: June 14, 2026
Reviewed by: Madeline Miceli, MD
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