A new study has reported that higher degree of European ancestry is associated with increased risk of breast cancer in Mexican women. The rate of breast cancer has been reported to be 35% lower in Hispanic women than in non-Hispanic Caucasian women living in the San Francisco Bay area. The authors previously described a significant association between genetic ancestry and breast cancer risk in a population of U.S. Latinas. The present study was conducted in Mexico to take into account the possibility that this finding may have been influenced by U.S.-specific environmental exposures. The study included 846 Mexican women with breast cancer and 1,035 unaffected Mexican women. Genetic ancestry was estimated using 106 ancestry-related markers, which were genotyped in all of the study participants.

Consistent with the previous study, greater European ancestry was found to be associated with increased risk of breast cancer in this group of Mexican women. Compared to women with 0% to 25% European ancestry, women with 51% to 75% European ancestry had a 35% increased risk of breast cancer. Women with 76% to 100% European ancestry had over twice the risk of breast cancer. For every 25% increase in European ancestry, there was a corresponding 20% increase in breast cancer. The authors conclude that nongenetic factors play a crucial role in explaining the difference in breast cancer incidence between Latinas and non-Latina Caucasian women, however, there may also be a genetic component to this difference.