While the drug tamoxifen reduces the risk of developing breast cancer and prevents recurrence, the side-effects cause many women to discontinue their treatment.
In a new study, researchers found that a much lower dose than the standard produces a good effect with fewer adverse reactions in women.
The research was conducted by a team at Karolinska Institutet and elsewhere.
The anti-hormone drug tamoxifen has been used for over 40 years to reduce the risk of relapse in women who have been treated for hormone-related breast cancer.
It is also approved as a prophylactic for women with an inherited higher risk of breast cancer.
Women with dense breasts, which is to say breasts with relatively high amounts of firbroglandular tissue to fat tissue, run a four to six-times higher risk of developing breast cancer.
Both dense breast tissue and tumors appear white in mammograms, which makes cancer difficult to detect. Tamoxifen reduces the mammographic density of the breast.
Despite the fact that tamoxifen reduces the risk of breast cancer by up to 40%, it is used relatively infrequently as a prophylactic for healthy women with an increased risk of the disease.
Almost half of the women who take tamoxifen to prevent recurrence after a lumpectomy discontinue treatment prematurely due to a number of known adverse reactions, including menopausal-like symptoms such as flushes, sweats, insomnia and various gynecological problems.
In the study, the team examined the effect of tamoxifen on breast density at a lower dose than the standard 20 mg.
They monitored 1,440 women between the ages of 40 and 74 for just under three years.
The women were randomly assigned to six groups of 240, five experimental groups that received a particular dose of tamoxifen (1 2.5, 5, 10 or 20 mg) plus a placebo group.
The established tamoxifen dose is 20 mg, but it turned out that 2.5, 5 and 10 mg reduced the density just as much as 20 mg.
At the same time, the adverse reactions reported by the 2.5 mg group were reduced by 50 percent compared to women who received the 20 mg dose.
The next step for the researchers is to examine whether 2.5 mg tamoxifen also reduces the risk of developing breast cancer and can therefore be used to prevent both a first occurrence and recurrence.
The study is published in the Journal of Clinical Oncology. One author of the study is Professor Per Hall.
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