Abstract PS5-12-11: Clinicopathological Characteristics and Treatment Patterns in Young Women with Breast Cancer at the Brazilian National Cancer Institute

Abstract Background: Breast cancer in women aged 40 years or younger is typically associated with more aggressive biological behavior and unfavorable prognosis. In low- and middle-income countries, healthcare system limitations may further impact outcomes. In Brazil, data specifically characterizing this population remain scarce. Objectives: To describe the epidemiological and clinicopathological features, and treatment patterns, among young women with breast cancer treated at a public cancer center. Methods: This retrospective observational study included young women (aged 18-40 years) with breast cancer who were registered at the Brazilian National Cancer Institute (INCA) between October 2022 and October 2023. Data were extracted from medical records. Results: Among 1,321 patients registered at the Breast Cancer Department during the study period, 75 (5.7%) were aged ≤40 years and included in the analysis. The median age at diagnosis was 37 years, and 68% of patients were non-white. A family history of breast cancer was reported in 45.3%, and 5.3% had a family history of ovarian cancer. At the time of diagnosis, 5.3% of patients were pregnant. Invasive carcinoma of no special type was the most common histologic subtype (82.4%), followed by other subtypes (12.2%) and lobular carcinoma (5.4%). Regarding histologic grade, 4.2% of tumors were grade 1, 68.1% grade 2, and 27.8% grade 3. Clinical stage (AJCC 8th edition) at diagnosis was: stage I: 6.7%, stage II: 38.7%, stage III: 34.7%, and stage IV: 20%. T classification: T1: 8.1%, T2: 31.1%, T3: 25.7%, and T4: 35.1%. Nodal status: N0: 41.3%, N1: 37.3%, N2: 16%, and N3: 5.3%. High Ki-67 (≥20%) was observed in 87.5% of tumors. Estrogen and progesterone receptor positivity were 74.3% and 66.2%, respectively; HER2 positivity (IHC 3+ or FISH positive) was observed in 27.4%, and 17% of tumors were triple-negative. Among the 60 patients with stage I-III disease, 78.3% received neoadjuvant chemotherapy. Surgery was performed in 86.7% of patients, with 67.3% undergoing mastectomy and 32.7% breast-conserving surgery. Among those who underwent mastectomy, more than half (54.2%) did not undergo breast reconstruction. Sentinel lymph node biopsy was performed in 61.6%, and axillary dissection in 38.4%. Conclusions: Young women with breast cancer treated at the Brazilian National Cancer Institute appear to present with advanced-stage disease, high-grade tumors, elevated Ki-67, and nodal involvement. Limited access to breast reconstruction was also observed. These findings highlight the need for targeted strategies to improve care delivery and outcomes for this population. Citation Format: M. F. de Melo, A. Boukai, . Clinicopathological Characteristics and Treatment Patterns in Young Women with Breast Cancer at the Brazilian National Cancer Institute abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-12-11.