Background: According to internationally published data, 35.2–64.4% of breast cancer cases are with HER2-low expression (Gampenrieder et al., 2021; Miglietta et al., 2021; Horishawa et al., 2021) out of all the breast cancer cases with identified HER2 expression (HER2 0, HER2 1+, HER2 2+, HER2 3+). This study aimed to determine HER2-low breast cancer epidemiology data in Lithuania and compare it with officially published data from clinical trials and epidemiologic studies.