A new study has shown that in breast cancer patients, chemotherapy and tamoxifen separately, may reduce the risk of recurrence of breast cancer for at least 10 and 5 years respectively.
The risk of developing a cancer in the other breast is about two to six times higher for breast cancer patients than that for the general public.
Earlier studies have shown that taking tamoxifen for five years reduces the risk of cancer in the opposite breast in women suffering from estrogen receptor-positive breast cancer. However, these studies did not shed any light on the length of the protective effect.
The current study, led by Lisbeth Bertelsen, M.D., of the Danish Cancer Society in Copenhagen, looked into the link between tamoxifen and chemotherapy, either alone or in combination.
The researchers also examined the risk of cancer in the opposite breast among American and Danish women whose first diagnosis of breast cancer was before age 55.
The study involved 1,158 women who developed cancer in one breast and also 634 women who had cancer in one breast initially and then developed a second cancer in the other breast.
The chemotherapy treatment, when compared with no chemotherapy, was found to reduce around 43 percent risk for developing cancer in the opposite breast.
After the initial cancer diagnosis, this risk reduction continued for about 10 years and was found to be stronger among women who entered menopause within a year of their diagnosis.
A 34 percent reduction of the risk of a second breast cancer was found to be associated with Tamoxifen use as compared with no tamoxifen use, and this reduction lasted for about five years after diagnosis.
"Ovarian suppression caused by chemotherapy may have a role in the association, possibly in combination with a cytotoxic effect on [breast tumor cells]," wrote the authors of the study.
The study was published online recently in the Journal of the National Cancer Institute.