The clear association of TP53 PVs in very young women presenting only with DCIS is noteworthy and adds to the published association of HER2+ invasive disease in young women with TP53 PVs.32TP53 and BRCA1/2 PVs are of similar frequency in women with breast cancer <26 years but BRCA1/2 PVs predominate in those aged 26–30 years. Here, BRCA1 is linked to ductal breast carcinoma in situ.