Incidence, proportion and survival of stage IV breast cancer between 2010-2021.

e13041 Background: Breast cancer (BC) incidence is increasing. However, trends in incidence and proportion of de novo stage IV BC are underreported. Knowing whether the increase in BC incidence is due to stage I-III vs. stage IV cases has important policy and clinical implications. We aimed to evaluate incidence, proportion and survival of de novo stage IV BC between 2010 - 2021. Methods: Using data from Surveillance, Epidemiology and End Results, we calculated age-adjusted incidence rates of BC and assessed annual percentage change (APC) between 2010 - 2021. Among existing BC cases, we analyzed the proportion of stage IV in each year (y). We evaluated changes in BC-specific survival (BCSS) for patients (pts) with stage IV BC using multivariable Cox models stratified by tumor subtype (TS). Results: Between 2010 – 2021, there were 761,471 BC cases of which 43,934 (5.8%) were stage IV. From 2010-2021, the increase in incidence was: for stage IV from 9.5 to 11.2, for stage I-III from 163 to 177.4, and for unknown stage from 0.2 to 0.6 cases per 100,000 women, respectively (p<0.05 for each). The table shows increased incidence of stage IV in each TS with different magnitudes. Pts aged <40 y had the highest increase in incidence (APC 3.1%, p<0.05), which was driven by HR+ cases (table). Pts aged >74 y had the highest increase in triple-negative (TN) cases (APC 4.3%, p<0.05). The incidence of stage IV increased numerically across all races with the highest magnitude in Non-Hispanic Asian/Pacific Islander (APC 3.4%, p<0.05). Incidence of stage IV BC also increased significantly in males. The proportion of stage IV differed by TS with the highest in HR-/HER2+ (10.4%) and lowest in HR+/HER2- (4.4%), p<0.001. The proportion increased over 2010 – 2021 for each TS (p value <0.02 for each). For each additional y in 2010 – 2021, BCSS in pts with stage IV improved with adjusted hazard ratios of: 0.985 in HR+/HER2- (p<0.01), 0.955 in HR+/HER2+ (p<0.01), 0.958 in HR-/HER2+ (p<0.01), and 0.985 in TNBC (p=0.14). Conclusions: Incidence of de novo stage IV BC increased significantly overall and across ages and sexes between 2010 – 2021. Proportions of stage IV among existing BC cases also increased. Although BCSS is improving, further research is warranted to determine what factors are contributing to the observed increase in stage IV incidence, including potential changes in the natural history of BC, disease screening, or the incidence and mortality of other conditions, among others. Incidence rate APC in females with stage IV BC. APC (95% CI) Overall Age at diagnosis (y) <40 40-49 50-74 >74 Stage IV Overall 1.2 (0.8 , 1.6) 3.1 (2.2 , 4.0) 1.7 (0.5 , 2.9) 0.5 (0.1 , 0.9) 1.7 (0.4 , 3) HR+/HER2- 2 (1.5 , 2.6) 4.5 (2.9 , 6.1) 2 (0.5 , 3.6) 1.2 (0.4 , 2) 3.3 (1.8 , 4.8) HR+/HER2+ 1.6 (0.2 , 2.9) 3.4 (0.9 , 5.9) 2.7 (0.9 , 4.5) 0.4 (-1 , 1.8) 2.1 (-0.6 , 4.9) HR-/HER2+ 1.3 (-0.1 , 2.7) 0.8 (-4.1 , 6) 1.6 (-0.7 , 4) 1.2 (0.2 , 2.3) 1.1 (-1.4 , 3.7) TN 2.7 (1.4 , 4) 1.8 (-2 , 5.6) 2.5 (-1.1 , 6.2) 2.2 (1.2 , 3.3) 4.3 (1.9 , 6.8)