Real-world Data Evaluating Outcomes Following Neoadjuvant and Adjuvant Therapy in Patients with HER2-Positive Early Breast Cancer

Author(s):

Ana-Marija Bukovica Petrc, Marin Golcic, Doris Kolovrat, Tijaha Salopek, Alojzije Kosic, Iva Skocilic, Anita Beg, Sanja Ropac, Maja Kolak and Ivana Mikolasevic

Background: Human Epidermal Growth Factor Receptor (HER2)-positive breast cancer accounts for 15-20% of all breast cancer cases. Despite its biological aggressiveness, it shows high sensitivity to chemotherapy in combination with anti-HER2 therapy. This study aimed to assess the real outcomes of neoadjuvant and adjuvant treatment in patients with HER2 positive early breast cancer in this European region. Methods: A retrospective observational study conducted at the Clinical Hospital Center Rijeka, Croatia included 137 adult patients with histologically confirmed HER2-positive early breast cancer treated between October 2016 and May 2024. HER2 positivity was defined as IHC 3+ or IHC 2+ with a positive FISH result. Primary outcome measures included pathological complete response (pCR) and long-term survival. Results: The median age of the patients was 60.2 years. Neoadjuvant treatment was received by 62% of the patients, and adjuvant treatment by 35%. A high pCR rate of 56.5% was achieved in the neoadjuvant group, and 61.3% in the group with dual anti-HER2 blockade. Factors associated with higher pCR rates were HER2 3+ expression (p=0.003), lower expression of estrogen receptors (p=0.016), and higher Ki-67 index (p=0.006). The median time to recurrence was 8.0 years with a recurrence rate of 13.1%. pCR proved to be a strong prognostic factor, especially in patients with stage II, where no patient with pCR relapsed during follow-up. Conclusion: The results confirm the high efficacy of modern treatment protocols for HER2-positive breast cancer. Pathological complete response remains the strongest predictor of favorable outcomes, and its presence almost eliminates early recurrence in stage II disease.