Population genetics is changing how we think about cancer screening. This short report identifies ATM c.7374_7375insAlu as a founder pathogenic variant in French Canadians associated with increased risk of pancreatic and breast cancer. The broader point is clinical as much as genetic: populations with shared ancestry can carry recurrent disease-causing variants that may be overlooked in more general testing strategies. Screening is therefore more informative when it takes population history into account. Rather than using the same approach for everyone, clinicians can adapt testing panels to variants that are more relevant in specific groups. That improves carrier detection, cascade testing in families, and surveillance for people at increased risk. (https://jmg.bmj.com/content/early/2026/03/31/jmg-2025-111441)