Abstract P3-07-08: Breast-Conserving Surgery in US Young Women With Early-Stage, HR-Positive/HER2-Negative Breast Cancer: National Trends and Oncologic Outcomes after Neoadjuvant Systemic Therapy

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Abstract Background: In the United States, the incidence of breast cancer for young women has been rising in recent years. Neoadjuvant chemotherapy (NACT) or neoadjuvant endocrine therapy (NET) is often used to downstage tumors allowing for breast-conserving surgery (BCS) among patients with early-stage, HR-positive/HER-negative breast cancer clinically. However, there is a paucity of data on BCS trends and associated treatment response and long-term survival as compared to mastectomy in the young patient population nationally. Methods: We analyzed real-world data from the 2010-2020 National Cancer Database. This retrospective study was restricted to female patients aged <40 years with stage I-III, HR-positive/HER-negative breast cancer and included 2 treatment cohorts: NACT and NET. Surgery type was classified as mastectomy and BCS. Pathologic complete response (pCR) was defined as ypT0/Tis ypN0. We fit log-binomial regression models to assess trends in BCS and percent change per year (95% CI). Overall survival was event or censored at the time of death from all causes or last known patient contact. Estimated 5-year and 10-year probabilities of overall survival with 95% CIs were generated and compared using the Kaplan-Meier method and the log-rank test stratified by surgery type for both treatment cohorts. Results: Of 4,561 patients treated with NACT, 35.0% underwent BCS, with a significant increasing trend from 31.0% in 2010 to 41.7% in 2020 (P for trend < 0.001; percent increase per year 2.6 [95% CI: 1.3-4.0]). Of 956 patients treated with NET, 33.7% underwent BCS and there was a significant increasing trend from 28.1% in 2010 to 44.1% in 2020 (P for trend = 0.001; percent increase per year 6.0 [95% CI: 2.6-9.5]). Young patients who achieved a pCR after NACT were more likely to have undergone BCS than those who did not (42.7% vs 33.9%; P < 0.001). Similarly, young patients who achieved a pCR after NET also had a greater likelihood of having undergone BCS than those who did not (46.9% vs 32.7%; P = 0.021). In the NACT cohort, compared to patients who underwent a mastectomy, those who underwent BCS had longer 5-year overall survival (89.9% [95% CI: 87.7-91.6%] vs 82.8% [95% CI: 81.1-84.5%]) and 10-year overall survival (80.1% [95% CI: 75.5-83.8%] vs 65.9% [95% CI: 62.1-69.5%]) (P < 0.001). In the NET cohort, patients who underwent BCS also had longer 5-year overall survival (93.3% [95% CI: 87.7-96.4%] vs 85.3% [95% CI: 80.9-88.8%]) and 10-year overall survival (91.0% [95% CI: 84.2-94.9%] vs 71.5% [95% CI: 62.6-78.6%]) than those who underwent a mastectomy (P = 0.002). Conclusions: In this US national sample of young women with early-stage, HR-positive/HER-negative breast cancer, BCS rates increased significantly from 2010 to 2020, and achieving a pCR was associated with higher rates of BCS in both NACT and NET cohorts. Regardless of neoadjuvant treatment modality, young patients who underwent BCS had better long-term overall survival than those who underwent a mastectomy. Our findings highlight the benefit of neoadjuvant systemic therapy for BCS eligibility in young patients who achieve a pCR and improved survival among those who underwent BCS, which suggests the need for strategies to address disparities in treatment response and mortality. Etiologies of these disparities in the young patient population also require further investigation. Citation Format: Jincong Freeman, Jared H. Hara, Ted O. Akhiwu, Shreyas Kalantri, Adam W. Scott, Heather J. Hoffman. Breast-Conserving Surgery in US Young Women With Early-Stage, HR-Positive/HER2-Negative Breast Cancer: National Trends and Oncologic Outcomes after Neoadjuvant Systemic Therapy [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P3-07-08.

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