Abstract

Background: Early-onset breast cancer (EOBC), defined as breast cancer in women under 45 years, is often associated with more aggressive biological behavior and poorer prognosis compared to older patients.

Objectives: (1) To evaluate the clinicopathological, immunohistochemical characteristics, and molecular subtypes of EOBC; (2) To investigate the associations between selected clinicopathological features and immunohistochemical profiles.

Materials and methods: A retrospective cross-sectional study was conducted on 72 patients with invasive breast cancer aged <45 years at Hue University of Medicine and Pharmacy Hospital from January 2023 to December 2025.

Results: The majority of tumors were >2 cm, with a high rate of lymph node metastasis (61.1%); most patients presented at stage II (54.2%). Invasive carcinoma of no special type (83.3%) and histological grade II (56.9%) predominated. Hormone receptor positivity was observed in 70.8% (ER) and 69.4% (PR) of cases, while a high Ki-67 index (≥20%) was present in 69.4%. Luminal B was the most common molecular subtype (38.0%). Significant associations were found between tumor size and clinical stage, as well as between histological grade and both hormone receptor status and molecular subtype (p < 0.05).

Conclusion: EOBC in this study demonstrates aggressive clinicopathological features and distinct molecular profiles, highlighting the critical role of tumor biology in disease behavior and its potential therapeutic implications.

Keywords: early-onset breast cancer, immunohistochemistry, molecular subtype.