Women with hereditary cancer in one breast, not related to the BRCA1 or BRCA2 genes, have a high risk of developing cancer in the other breast, Swedish investigators report. Patients who have breast cancer diagnosed before the age of 50 are at the highest risk, but hormone therapy reduces the risk.

Women with a hereditary breast cancer have a two- to six-fold greater chance of developing cancer in the other breast compared with the risk in women in the general population. While it is recognized that the risk of a cancer in the opposite breast is even greater among those with BRCA-related cancers, Dr. Henrik Gronberg and colleagues point out that no one has evaluated the risk among women with non-BRCA hereditary breast cancer.

Gronberg, from Karolinska Institute in Stockholm, and his associates therefore followed for 204 women with hereditary non-BRCA breast cancer for around 7 years.

They report their findings in the current issue of the journal Cancer.

During the study period, there were 25 cancers in the opposite breast in a population in which the expected number is about 5. Among women who developed cancer before age 50 years, the probability of a cancer in the other breast was 41 percent at 20 years compared with 10 percent among women diagnosed later in life. In contrast, the risk at 20 years for a second cancer in the other breast in the general population was 4.9 percent.

Younger age and not receiving hormone therapy such as tamoxifen raised the risk of cancer occurring in the opposite breast.

The authors observed no effect of chemotherapy, but studies involving far more women have shown that therapy seems to reduce the cancer risk in the opposite breast.

In younger women with non-BRCA hereditary breast cancer, prophylactic removal of the unaffected breast may be an option, Gronberg’s group notes. For postmenopausal women, however, monitoring and treatment with hormone therapy is a sensible strategy, they add.

SOURCE: Cancer, March 15, 2006.