Abstract PS4-12-23: Regional variability and healthcare disparities in the management of early-onset breast cancer in Peru

Abstract Background: Breast cancer is the most common malignancy among women in Peru, with around 7,800 new cases and nearly 2,000 deaths each year. The National Cancer Institute (INEN) in Lima receives approximately 1,200 new cases annually, reflecting the high burden concentrated in the capital. Breast cancer in young women (≤45 years) represents a particular clinical challenge due to its association with more aggressive behavior and poorer prognosis. Although international evidence suggests that clinical presentation may vary by population and geography, data on regional differences within Peru remain scarce. Objective: To analyze regional differences in the distribution in young women breast cancer subtypes in Peru, including the incidence of Luminal A, Luminal B, HER2+, and triple-negative tumors, along with associated clinicopathological features and treatment response. Methods: This observational, cross-sectional, multicenter study included women aged ≤45 years with stage II-III breast cancer diagnosed between 2021 and 2023, all of whom received neoadjuvant therapy, across three Peruvian macro-regions: Lima, the Northern Coast, and the Southern Highlands. The sampling design was based on the regional epidemiological burden and operational capacity of participating centers, allocating 92 patients to Lima (≈60%), 34 to the Northern Coast (22.7%), and 23 to the Southern Highlands (15.3%). The sample size ensured 80% statistical power (α=0.05) to detect ≥20% differences in the most frequent subtypes, with Fisher’s exact test applied to comparisons with small frequencies to ensure robust interregional analyses. Results: A total of 149 young women with breast cancer were analyzed across three Peruvian macro-regions: Lima (93; 62.4%), Northern Coast (33; 22.1%), and Southern Highlands (23; 15.4%). Median age at diagnosis was 39, 41, and 38 years respectively, showing a homogeneous pattern with slight regional variation. Stages II-III predominated, with a higher proportion of advanced cases in the Southern Highlands (∼65%). Invasive ductal carcinoma was the main histology (>85%), while high-grade tumors were more frequent in the Southern Highlands (∼47%). Molecular subtype distribution varied: Luminal B was predominant in Lima (∼42%), HER2+ in the Northern Coast (∼36%), and triple-negative in the Southern Highlands (∼26%). Pathological complete response (RCB 0) was highest in Lima (∼28%), intermediate in the Northern Coast (∼21%), and lowest in the Southern Highlands (∼13%). Breast-conserving surgery was more common in Lima (∼35%), while mastectomy predominated in the Northern Coast and Southern Highlands (>70%). Radiotherapy coverage was uniform across regions (>85%). Conclusions: These findings reveal regional differences in young women breast cancer across Peru, likely influenced by inequities in access to specialized care and treatment standardization. This highlights the need for strategies to improve early diagnosis and harmonize management to achieve better outcomes. Larger studies with more representative samples and reduced bias are required to better reflect the national reality Citation Format: I. Otoya, C. Calle, N. Valdiviezo, Z. Morante, J. Moreno, S. Lozano, M. Valdivia, G. Valencia, L. Sanchez, T. Vidaurre, V. Acuña, S. Neciosup. Regional variability and healthcare disparities in the management of early-onset breast cancer in Peru [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 PS4-12-23.