Several trials have established the benefits of tamoxifen for the adjuvant treatment of early-stage breast cancer, particularly in women with estrogen receptor-positive disease. However, many women stop taking tamoxifen before completing their treatment course. The Cancer Research UK 'Over 50s' trial, led by Allan Hackshaw and coauthors, is one of the largest multicenter, randomized trials ever conducted that has compared 2 years and 5 years of tamoxifen use. Now, this trial reports the long-term results after a median follow up of 10 years.

Hackshaw's team were interested in the long-term benefits of tamoxifen use. The trial showed that completion of 5 years of tamoxifen significantly reduced the occurrence of a breast cancer returning in the same breast, and also reduced the risk of a new breast cancer developing in the contralateral breast. This benefit was noted even 10 years after stopping tamoxifen. Importantly, there was also a clear reduction in the risk of developing cardiovascular disease and mortality in women who took tamoxifen for 5 years, especially those aged 50 to 59 years. As Hackshaw summarizes, “this trial is the first to show that most of the benefit is among younger women. Therefore, 5 years of tamoxifen has the expected advantage of better outcomes associated with breast cancer, and an additional—not well known—benefit on heart disease”. It is hoped that the results of this trial will encourage women who are taking tamoxifen to complete 5 years of treatment. Hackshaw notes, “trials of 10 years of tamoxifen use are due in the next few years. If the results from these trials show a benefit, then encouraging women to finish 5 years might help them to complete 10 years.”