(Ivanhoe Newswire) – Breast cancer patients may reduce the risk of developing a second cancer in their other breast if they have chemotherapy or tamoxifen.

The risk of developing cancer in the other breast is two to six times greater for breast cancer patients than the general population’s risk for any breast cancer at all. Research has shown taking tamoxifen for five years reduces the risk of cancer in the opposite breast in women with estrogen receptor-positive breast cancer but it is not known how long the protective effect lasts.

Researchers from Copenhagen looked at the relationship between tamoxifen and chemotherapy – both alone and in combination – and the risk of cancer in the opposite breast in American and Danish women first diagnosed with breast cancer before age 55. Participants were 1,158 women with cancer in one breast and 634 who first got cancer in one breast then developed a second cancer in the other breast.
 

Results show chemotherapy reduced the risk of developing cancer in the opposite breast by 43 percent compared to not having any chemotherapy. The reduced risk lasted up to 10 years after the cancer was first diagnosed and was stronger among women who started menopause within a year of their diagnosis.

The study also shows taking tamoxifen reduced the risk of a second breast cancer by 34 percent compared to not taking tamoxifen. This effect lasted five years after diagnosis.

The authors conclude, “The associations between chemotherapy and tamoxifen treatment and reduced risk for contralateral breast cancer appear to continue for 10 and 5 years, respectively, after the initial breast cancer is diagnosed. Ovarian suppression may have a role in the association between chemotherapy and reduced risk for contralateral breast cancer.”

SOURCE: Journal of the National Cancer Institute, published online Dec, 2007