Previously there was not a clear answer as to the best time to start tamoxifen and whether this should be given at the same time as chemotherapy or after this was completed. However, recent research has been done to help answer this question. This was a large study, which looked at the timing and benefit of chemotherapy and tamoxifen treatments, following surgery for early stage breast cancer.

The results found that giving tamoxifen treatment once chemotherapy was complete was more effective in preventing cancer returning, than if they were given at the same time. The authors also suggested that if tamoxifen and chemotherapy were taken together, tamoxifen may cut the effectiveness of chemotherapy.

Although further follow-up of women in this study is still needed to confirm that this benefit continues over time, the findings now support starting tamoxifen once chemotherapy is complete.