Background: The aim of the present study was to evaluate how breast cancer prognosis has evolved over time in young women treated with breast-conserving surgery (BCS). Methods: Data from patients younger than 40 years who had BCS and whole-breast radiotherapy in a single cancer centre between 1997 and 2010 were analysed. The patients were followed until 2016. Endpoints were local recurrence, any breast cancer-related event and death from any cause. Results: A total of 1331 patients were included in the study. After a median follow-up of 9·3 years, 114 local recurrences, 289 breast cancer-related events and 138 deaths had occurred. Women were divided into three groups of similar size based on tertiles of the date of diagnosis: 1997–2002 (524 patients), 2003–2005 (350) and 2006–2010 (457). The risk of local recurrence was 1·42 per 100 person-years in women diagnosed in the first interval, 0·85 per 100 person-years in the second and 0·48 per 100 person-years in the third (P for trend = 0·028). The respective values were 3·01, 2·52 and 2·07 per 100 person-years for any breast cancer-related event (P = 0·004), and 1·59, 1·22 and 0·64 per 100 person-years for death (P = 0·003). Each passing year was associated with a decreasing risk of local recurrence (hazard ratio (HR) 0·93, 95 per cent c.i. 0·87 to 1·00), any breast cancer-related event (HR 0·94, 0·91 to 0·98) and death (HR 0·89, 0·83 to 0·94). A major improvement in prognosis was observed after 2005, when the classification of breast cancer molecular subtypes and use of trastuzumab were implemented in routine clinical practice. Conclusion: In the past two decades, both local control and overall prognosis have improved significantly in young women (aged less than 40 years) with breast cancer who undergo BCS.
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