Abstract: Breast cancer in younger patients exhibits stronger invasiveness and poorer outcomes compared with that in elders. Cut-off for young age remains unclear, and its basis as prognostic factor representing a continuous variable requires further investigation. Pregnancy-associated breast cancer in young patients also possesses unique biological features. In this review, we define breast cancer diagnosed in patients below 25 years old as very young breast cancer and summarize recent studies based on genetic factors, clinicopathology, prognostic characteristics, and pregnancy-associated breast cancer to assist in management of very young breast cancer patients.