Research from Belgium and the Netherlands has shown that the menstrual cycle can influence the effectiveness of chemotherapy in breast cancer treatment.

Historically, women have been underrepresented in medical research, partly due to the complications of designing animal studies in females because of hormonal fluctuations. This study explored how these hormonal changes might actually be vital to effectively treat breast cancer.

Researchers from EARA members the Netherlands Cancer Institute (NKI) and VIB Institute for Cancer Biology, in Belgium, showed, in female mice with breast cancer, that chemotherapy worked better to eliminate cancer cells if it was applied during a specific phase of the mouse menstrual cycle.

Colinda Scheele, a lead researcher at VIB, explained: “We observed a sensitive phase of the cycle in which the chemotherapy killed more cancer cells [and that] the sensitivity to the chemotherapy remained, even after the cycle stopped as a result of the treatment.”

The study in Nature showed that this increased sensitivity, from cancer cells, to chemotherapy was likely due to immune cell activity and increased blood vessel activity in breast tissue during that specific phase.

The research team is now setting up a national study with 100 women with breast cancer, funded by the Oncode Institute, to analyse if there is a link between the treatment outcome and the menstrual cycle, by collecting blood samples.