Long-term observational follow-up study of breast cancer diagnosed in women ≤40 years old.

The prognosis of young breast cancer patients has been considered to be much poorer than in older patients. Two hundred and sixty-eight premenopausal women with a median follow-up time of 74.0 months were included in the study. 33.5% had oestrogen receptor-negative and 34.6% progesterone receptor-negative tumours. 15.2% of the tumours were HER2-positive. Five-year breast cancer-specific survival (BCSS) was 81.1% and the corresponding 10-year figure was 72.3%. 91.8% of all relapses occurred within seven years of surgery. Among the ≤35-year-old women, only 2 of 38 (5.3%) relapsed beyond seven years of follow-up. Lymph node ratio was the most significant independent prognostic factor of poor disease-free survival and BCSS. This study revealed a high relapse rate in the youngest women as early as during the first few years after diagnosis, although their prognosis as a whole was surprisingly good.