The trial team found that low dose oestrogen worked for some women in this small trial. And the side effects were acceptable, apart from vaginal bleeding.
This phase 2 trial
took place in the UK. The researchers published the results in 2015.
The trial team found it was difficult to find enough women to take part, so the trial closed earlier than planned. This was mainly because women didn’t want to take low dose oestrogen as their previous treatment was directed at reducing oestrogen concentrations.
21 women joined the trial and the researchers had the results for 19. Treatment was in 3 stages, as follows:
- low dose oestrogen (oestradiol)
- high dose oestrogen
- an aromatase inhibitor
Everyone took low dose oestrogen until it stopped working. They then had the option to try high dose oestrogen if their doctor thought it could work.
They then restarted the aromatase inhibitor they were taking before the trial if either dose of oestrogen worked. This is because the oestrogen may have made the cancer sensitive to aromatase inhibitors again.
The trial team looked at how well low dose oestrogen (oestradiol) worked. They found in:
- 5 women treatment worked and the cancer stayed stable
- 14 women the cancer got worse
On average, the cancer stayed the same for about 17 months.
3 out of 5 women went on to have high dose oestrogen when oestradiol stopped working. Of those 3 women, the cancer shrank significantly in 1. This is called having a partial response to treatment.
Of the 5 women who had oestradiol that worked, 4 restarted their aromatase inhibitor. They looked at how well this worked.
- 3 women the cancer remained stable for at least 6 months
- 1 woman the cancer shrank significantly
The trial team say that low dose oestrogen seemed to work best in women whose first aromatase inhibitor hormone therapy had also worked well and controlled the cancer for a long time.
The most common side effects of oestradiol were:
- feeling or being sick
- tiredness (fatigue)
- breast pain
- vaginal bleeding
8 women had vaginal bleeding, and this was the most common side effect. 4 women had to stop treatment because of side effects.
The trial team concluded that lose dose oestrogen worked for some women with advanced breast cancer. And giving an aromatase inhibitor afterwards works and shows that the cancer can become sensitive to them again. But this was a small trial and although the side effects were acceptable, vaginal bleeding was a problem.
We have based this summary on information from the research team. The information they sent us has been reviewed by independent specialists (peer reviewed
) and published in a medical journal. The figures we quote above were provided by the trial team who did the research. We have not analysed the data ourselves.