Chemo, tamoxifen cut risk of second breast cancer

NEW YORK (Reuters Health) - Among women with breast cancer, both chemotherapy and tamoxifen reduce the long-term risk of developing a second cancer in the other breast, researchers report in the January 2, 2008 issue of the Journal of the National Cancer Institute. The risk reduction persists for at least 10 years with chemotherapy and for 5 years with tamoxifen.

For breast cancer patients the risk of developing cancer in the other breast is two to six times greater than the breast cancer risk of the general public. Previous reports have shown that both chemotherapy and tamoxifen reduce the risk of "contralateral" breast cancer, but the length of this reduced risk was unclear.

Dr. Lisbeth Bertelsen, from the Danish Cancer Society in Copenhagen, and colleagues report investigated the relationship between tamoxifen and chemotherapy -- either alone or in combination -- and the risk of cancer in the opposite breast among American and Danish women who were first diagnosed with breast cancer before age 55.

The study included 1,158 women who developed cancer in one breast and an additional 634 who initially had cancer in one breast then developed a second cancer in the other breast.

Results showed that chemotherapy was associated with a 43 percent reduced risk for developing cancer in the opposite breast, compared with no chemotherapy. This risk reduction lasted up to 10 years after the initial cancer diagnosis.

Tamoxifen use was associated with a 34 percent reduced risk of a second breast cancer, compared with no tamoxifen use, and this reduction continued for five years after diagnosis.

SOURCE: Journal of the National Cancer Institute, January 2, 2008.