A new study has reported that the risk of breast cancer among BRCA1 mutation carriers who reside in Poland is lower than that of BRCA1 carriers in North America. BRCA1 mutation carriers face a high lifetime risk of breast cancer. However, not all carriers develop breast cancer and it is unknown to what extent environmental factors influence the risk. Non-genetic risk modifiers are likely to be present if women from different geographical areas with similar mutations experience different rates of breast cancer.

The study comprised 1477 women with a harmful BRCA1 mutation, including 256 from the U.S., 358 from Canada, and 863 from Poland. The women were followed for an average of 4.3 years, during which time 130 cases of breast cancer were diagnosed. Cancer incidence rates were estimated based on this data.

Residence in Poland was found to be associated with approximately half the risk of breast cancer compared to residence in North America. The cumulative risk of breast cancer to age 70 was estimated to be 49% for women in Poland compared to 72% for women living in North America. The authors conclude that the risk of breast cancer in women who reside in Poland is lower than that of women in North America among BRCA1 mutation carriers. The reasons for the difference are unknown, but the findings suggests that environmental factors or genetic modifiers are important.

Please see our article on breast cancer diet for BRCA mutation carriers for more information on how diet and lifestyle could influence breast cancer risk among carriers.