Very rare syndromes such as Li-Fraumeni syndrome (TP53), Cowden/PTEN hamartoma syndrome (PTEN), Peutz-Jeghers syndrome (STK11) and hereditary diffuse gastric cancer and lobular breast cancer (CDH1) are all considered to be associated with high breast cancer risks [11], but due to the rarity of pathogenic variants and ascertainment bias in published studies, risk estimates are uncertain. Here, STK11 is linked to breast cancer.