A total of 63 women diagnosed with invasive breast cancer at 35 years or younger in the South Swedish Health Care Region between January 1, 2000 and December 31, 2017, who had not previously been registered at the Oncogenetic Clinic at Skåne University Hospital in Lund, were offered analysis of the genes BRCA1, BRCA2, PALB2, CHEK2, and ATM. Median ages at diagnosis and study invitation was 34.2 (range: 25.3–35.9) and 45.8 (33.0–54.2) years, respectively. This evidence concerns the gene CHEK2 and invasive breast carcinoma.