Data was obtained from 206,156 of YBC. We see an uptrend in the number of incident cases that are being diagnosed each year. There was a large drop off in the number of incident cases for 2020, which was the year of the COVID-19 pandemic. The number of cases increased from approximately 10,000 in 2004 to almost 15,000 diagnosed in 2019 (Fig. 1).

Cases of YBC diagnosed each year. The chart shows the trend that the number of cases diagnosed each year is increasing. There is a drop-off during the year 2020, likely related to the COVID-19 pandemic

Overall, there were 55,397 patients diagnosed between 2005 and 2009 (Old) and 67,930 patients diagnosed between 2015 and 2019 (New). Median age in both groups was 37. Approximately 99% of the cases were diagnosed in women (Table 1).

Comparison of demographic data between the Old and New group were completed (Table 1). It showed significant increase in the proportion of Hispanic (4575 (8.4%) vs 6720 (10.0%)), Black (8695 (16.0%) vs 11,156 (16.6%)), and Asian (2592 (4.8%) vs 4512 (6.7%)) populations (p < 0.001). There was a significant increase in the proportion of patients with Medicaid (5893 (11.0%) vs 10,694 (16.0%), p < 0.001). There was no significant difference in populations when looking at reported income (p = 0.186). Additionally, there was no significant difference in the type of community patients were living in, with the majority (approximately 90%) of patients reporting living a Metro setting (p = 0.088).

Clinical data was also compared between the Old and New Group (Table 2). For histologic data, there is an increase in the proportion of patients with Invasive Ductal Carcinoma (IDC) (38,282 (69.1%) vs 50,919 (75%)) and Invasive Lobular Carcinoma (ILC) (1357 (2.4%) vs 1823 (2.7%)) with a p value < 0.001. There is also an increase in the proportion of patients whose histology is graded as moderate (17,162 (34.7%) vs 23,631 (38.5%)) with a reduction in the proportion of patients whose histology was graded as poor (26,747 (54.1%) vs 31,732 (51.8%)) with a p value < 0.001. There is a significant increase in the proportion of patients with HR positive disease (HR+) (35,142 (70.0%) vs 49,409 (75.8%), p < 0.001), with a decrease in the proportion of patients who have HR negative disease (HR-) (15,058 (30.0%) vs 15,814 (24.2%), p < 0.001). There is a significant increase in the proportion of patients who did not receive chemotherapy (p < 0.001), although this is likely clinically insignificant given small proportional increase from 29.6 to 30.7%. We see a slight decrease in patients who received radiation therapy from 51.4 to 49.9%, p < 0.01 Unsurprisingly, given the increase in HR + disease, we see a significant increase in the number of patients treated with hormonal therapies (24,447 (46.8%) vs 38,483 (58.3%), p < 0.001).

The OS of patients from the New group was compared across various demographic and clinical characteristics (Table 3). Interestingly, race and ethnicity appeared to have a large impact on survival with Black patients having a statistically significant worse overall survival (Hazard ratio 1.24 (1.13–1.35), p < 0.001), while Hispanic White and Asian patients had improved OS (Hazard ratio 0.87 and 0.78, p = 0.024 and p = 0.007, respectively) as compared with Non-Hispanic White patients. Private insurance had the best overall survival, while Medicaid, Medicare, and being uninsured all have worse survival outcomes (p < 0.001). Patients who reported incomes less than $38,000 had worse overall survival as compared to patients who reported to have incomes above $63,000 (p < 0.001). Like historic data, as the stage at diagnosis became more advanced, we saw increasingly worsening OS. The patients who underwent treatment with either chemotherapy, radiation, or hormonal treatment, all had improved OS and those who refused chemotherapy or hormonal treatment having significantly worsened survival (p < 0.001).