Introduction/Background The administration of neoadjuvant chemotherapy (NACT) has revolutionized the therapeutic strategy for breast cancer (BC). The latter constitutes a public health problem, occupying first place among women’s cancers in Tunisia and worldwide. Although the evaluation of the response to NACT is multidisciplinary, histological examination remains the cornerstone of this assessment. The aim of this work was to evaluate the response to NACT of HER2-positive BC and to determine the clinicopathological factors predictive of a good response to this therapy.

Methodology Descriptive, retrospective, cross-sectional study carried out over a 5-year period from January 1, 2018, to December 31, 2022, involving 58 patients operated on and confirmed at the Salah Azaiez Institute in Tunis for breast carcinoma who received CTNA.

Results We included 58 patients. The mean age was 49 years. The mean tumor size was 74 millimeters. All tumors studied were of high SBR grade (grade III: 36 cases, 62%, and grade II: 22 cases, 38%). The predominant molecular type in our series was HER2-positive luminal B (45 cases, 78%), followed by HER2-amplified (13 cases, 22%). We had 19 cases (33%) of complete pathological response, 18 cases of partial response (31%), and 21 cases (36%) of chemoresistance. The study of the correlation between the various parameters (clinical, microscopic, and IHC) with the RCB classification showed a significant correlation with: age, tumor size, bilaterality, tumor emboli, lymph node involvement, quality of surgical excision limits, and TNM staging. In multivariate analysis, the parameters significantly affecting the nature of response to CTNA were: lymph node metastasis (p<0.001), bilaterality (p=0.014), quality of surgical excision limits (p=0.014), tumor emboli (p=0.029), and tumor size (p=0.05).

Conclusion Pathological evaluation using the RCB classification is crucial in the management of HER2-positive breast cancers treated with CTNA, providing information on prognosis and improving post-operative management.

Disclosures Authors declare that they have no relevant or material financial interests that relate to the research described in this paper.