Impact of young age at diagnosis on survival outcomes in patients with early breast cancer according to tumor subtype: Pooled analysis of 5 randomized clinical trials from the Mammella InterGruppo (MIG) and Gruppo Italiano Mammella (GIM).

523 Background: The incidence of breast cancer (BC) among young patients is increasing. Historically, young age itself has been recognised as a poor prognostic factor for BC. However, there is limited evidence regarding the impact of age at diagnosis and on survival outcomesaccording to tumor subtype. Methods: We collected individual patient (pt)-level data from newly diagnosed stage I to III BC pts participating in 5 randomized clinical trials conducted by Mammella InterGruppo (MIG) and Gruppo Italiano Mammella (GIM) study groups. Patients were categorized into the following age groups based on their age at BC diagnosis: ≤40, 41-50, 51-60, 61-70, >70 years (yr). Multivariable Cox proportional hazards models were used to assess the relationship between age and breast cancer–free interval (BCFI) and breast cancer specific survival (BCSS). Results: 8,338 pts with stage I to III BC were included in the study: 778 (9%) aged ≤40 years, 1629 (20%) 41-50 years, 2,595 (31%) 51-60 years, 2,435 (29%) 61-70 years, and 901 (11%) >70 years. Compared to older, young pts were more likely to have ductal tumors as histology, larger than 2 cm, with nodal involvement, G3 and triple negative or HER2 positive subtypes (p<0.001). With a median follow-up of 9.0 years (IQR 5.5-14.4), 2,161 BCFI and 927 BCSS events were observed in the overall population. Pts ≤40 years at diagnosis had greater risk of reporting BC event (adjusted hazard ratio (adjHR) for BCFI 1.27, 95% CI 0.93-1.74) compared to pts aged 51-60 years (reference group), while pts 41-50 years had a lower risk (adjHR 0.74, 95%CI 0.55-0.99). Pts aged ≤40 years presented some evidence of a lower risk of BCSS events (adjHR 0.80, 95%CI 0.50-1.26) compared to pts aged 51-60 years, while pts aged 41-50 years had the lowest risk (adjHR 0.50, 95%CI 0.32-0.78). There was evidence of interaction between age and tumor subtype, nodal status both for BCFI and BCSS. A significant increase in risk of BC events was observed among pts ≤40 years with hormone-receptor positive/HER2 negative tumors (HR 1.70 for BCFI) and among ≤40 years with node negative tumors (HR for BCFI 2.43). Conclusions: The prognostic significance of young age at diagnosis may vary depending on tumor subtypes and nodal status, indicating poorer outcomes for young pts with hormone-receptor positive/HER2 negative and node negative tumors.