Location of residence and breast cancer stage: A SEER population-based analysis

To the Editor:
Location of residence may influence breast cancer risk, with several reports indicating that living in locations closer to the equator may reduce both incidence and mortality from breast cancer 1-4. For example, a recent, large French cohort study found that women who resided at southern latitudes (<46° N) had a 10% decreased risk of breast cancer compared to women living at northern latitudes (>49° N) 1. A combined analysis involving 175 countries found a dose-response relationship between breast cancer incidence rates and latitude, with rates increasing as the distance from the equator increased (R2 = 0.43; p < 0.001) 2. Furthermore, women over 50 years old living in the Northeast of the U.S. were found to have a 13% increased risk of breast cancer mortality compared to women in the South 4.