Breast Cancer Recurrence by Subtype in a Diverse, Contemporary Cohort of Young Women.

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: A retrospective review of YBC patients (age 40 years or younger) with stage I to III breast cancer diagnosed from 2008 to 2018 was performed. Information on clinicopathologic characteristics, demographics, and outcomes was obtained from the electronic health record and chart review. Chi-square and Fisher's 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 to 12.9 years). The median age was 37 years (interquartile range 34 to 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) + /human epidermal growth factor 2 (HER2 - ), grade (G) 1 to 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 of 463 (3.7%) patients who underwent breast conservation vs 41 of 968 (4.2%) patients undergoing mastectomy (p < 0.001). Recurrence varied by tumor subtype: [1] HR + /HER2 - , G1 to 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).

Conclusions: 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 vs mastectomy. Additional research is needed to identify predictors of recurrence.