Cyclophosphamide is a chemotherapy agent. The U.S. Food and Drug Administration (FDA) first approved the treatment in 1959. Doctors still use it to treat myeloma and other types of cancer. It is sold under the brand name Cytoxan. Generic versions of the treatment are available as a tablet or injection.

How does cyclophosphamide work?

Cyclophosphamide is in a class of medications called alkylating agents. The body metabolizes the small molecule within the medication to form a chemical that affects DNA and RNA within cells, slowing or preventing cell division.

Every cell in the body (including cancer cells) has a complete copy of the genome. Every time a cell divides it must make a copy of its entire genome. Many types of rapidly dividing cancer cells (including myeloma cells) have to copy their DNA quickly and frequently. Disrupting this process can cause cell division to pause. This can make cancer cells more vulnerable to attack from the immune system, radiation, or other chemotherapy treatments.

Cyclophosphamide modifies the DNA by adding an alkyl group to the bases. This causes the machinery that copies the DNA to make mistakes that change the DNA sequence. The chemical modification also signals to repair mechanisms within the cell that cut the DNA in an effort to replace the modified bases. Finally, cyclophosphamide cross-links DNA bases, forming a bond between strands of DNA. This prevents the unfolding of double-stranded DNA for the machinery that copies the DNA for cell division or the one that makes a temporary RNA copy of a gene (messenger RNA) as a template for making protein. Cross-linking the DNA in this way makes it harder for the cells to make copies of DNA, as well as blocking the synthesis of some proteins.

Cyclophosphamide in myeloma research

Several published case studies have indicated that cyclophosphamide may be useful in overcoming resistance in myeloma cases in which multiple other treatments have not halted disease progression.

One study, published in Anticancer Research, analyzed a 62-year-old patient with refractory myeloma. Doctors previously had treated the patient with six different treatment regimens, but she had not responded. She then received dexamethasone and low-dose cyclophosphamide. This resulted in a partial response (tumor reduction) to therapy that was maintained for almost two years. She tolerated the combination well with no severe adverse reactions. The authors suggested that some older medications like cyclophosphamide are still a viable option when treating refractory cases of myeloma.

Other case studies published in Case Reports in Hematology included two myeloma patients who were resistant to two other cancer treatments —  Velcade (bortezomib) or Revlimid (lenalidomide). Doctors treated both patients with cyclophosphamide as an add-on to their other treatments. In one case, the patient achieved a complete response while the other achieved a very good partial response.

The authors concluded that cyclophosphamide can help overcome resistance to treatment when used as an add-on therapy. They recommended that a larger study of the safety and effectiveness of this strategy is necessary.

Other information

Cyclophosphamide can cause side effects including anemia, hair loss, nausea, loss of appetite, and loss of fertility. Although rarer, cyclophosphamide also can cause bladder irritation and bleeding.


Last updated: Mar. 10, 2020


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