355eP HER2 status conversion after neoadjuvant therapy in breast cancer: Insights from a single-center series of 55 patients

Background: HER2-positive breast cancer represents a distinct subtype of the disease, characterized by more aggressive biological behavior but also by a strong sensitivity to anti-HER2 targeted therapies.The introduction of neoadjuvant treatments combining chemotherapy and anti-HER2 agents has profoundly transformed patient management by achieving high rates of pathological complete response (pCR), which is now recognized as a major prognostic indicator. Methods:We conducted a retrospective study over a five-year period, from January 1st, 2020 to December 31st, 2024, in the Medical Oncology Department of our cencter.The objective was to evaluate the clinical, therapeutic, and outcome characteristics of patients with localized HER2-positive breast cancer who received neoadjuvant treatment.Results: A total of 87 patients were included, with a median age of 49 years (range 27-72); 63% were premenopausal, 8% had hypertension, and 6.9% diabetes.Tumors were T1c-T4 (3.9-33.3%),with 54.9% having nodal involvement.All patients had localized invasive ductal carcinoma, HER2 3+ or 2+ amplified by FISH; 51% were hormone receptor positive and 55.8% had Ki-67 >20%.All received sequential chemotherapy (AC60/EC100 taxanes) with trastuzumab (90% subcutaneous) and pertuzumab in 63%.Surgery included mastectomy with axillary dissection (58.8%) and breast-conserving surgery (41.2%).pCR was achieved in 54.9%; among non-pCR patients, residual disease was ypT1 (56.5%), ypT2 (26.1%), ypT3 (17.4%), and ypN+ (30.4%).Patients achieving pCR were more often premenopausal (71.4% vs 60.9%) and had higher nodal involvement (64.3% vs 43.5%).All received adjuvant therapy; only 30.4% of non-pCR patients received T-DM1 due to limited availability.At followup, 90.2% remained in complete remission, while 9.8% relapsed, predominantly non-pCR patients (80%).Conclusions: Pathological complete response (pCR) is a key prognostic factor in localized HER2-positive breast cancer, with pCR patients showing better recurrencefree survival.These results stress the importance of effective neoadjuvant therapy and access to anti-HER2 treatments.