LAUSR

BACKGROUND Young breast cancer (YBC) patients are a unique subpopulation that are often underrepresented in randomized clinical trials. Furthermore, large national cancer databases lack detailed information on recurrence, a meaningful oncologic outcome for young patients. STUDY DESIGN Retrospective review of YBC patients (age ≤40) with Stage I-III breast cancer diagnosed from 2008 to 2018 was performed. Information on clinicopathologic characteristics, demographics, and outcomes were obtained from the electronic health record and chart review. Chi-square and Fisher exact tests were used for comparisons of categorical variables and parametric and nonparametric tests for continuous variables. RESULTS The cohort included 1,431 women with a median follow-up of 4.8 years (range: 0.3-12.9 years). The median age was 37 (IQR: 34-39). The study population included 598 (41.8%) White, 112 (7.8%) Black, 420 (29.4%) Asian/Pacific Islander, 281 (19.6%) Hispanic, and 20 (1.4%) "other" race/ethnicity patients. Tumor subtype was as follows: [1] Hormone Receptor (HR)+/HER2-, Grade (G) 1-2 =541 (37.8%); [2] HR+/HER2-, G3 =268 (18.7%); [3] HR+/HER2+ =262 (18.3%); [4] HR-/HER2+ =101 (7.1%); [5] HR-/HER2- =259 (18.1%). The majority (64.2%) presented with Stage II/III disease. There were 230 (16.1%) recurrences during follow-up; 74.8% were distant. Locoregional only recurrence was seen in 17/463 (3.7%) patients who underwent breast conservation versus 41/968 (4.2%) of patients undergoing mastectomy (p<0.001). Recurrence varied by tumor subtype: [1] HR+/HER2-, G1-2 (14.0%); [2] HR+/HER2-, G3 (20.9%); [3] HR+/HER2+ (11.1%); [4] HR-/HER2+ (22.8%); [5] HR-/HER2- (17.8%) (p=0.005). CONCLUSION In this large, diverse YBC cohort, recurrences were most frequent among HR+/HER2-, G3 or HR-/HER2+ invasive tumors; most were distant. There were numerically similar locoregional-only recurrences after breast conservation versus mastectomy. Additional research is needed to identify predictors of recurrence.