Consensus from the 2025 International Symposium on Breast Diseases of Inland São Paulo: Management of HER2-Positive Breast Cancer

Objective: To present the expert panel recommendations derived from the panel discussion “Management of HER2-Positive Breast Cancer”, held during the 2025 International Symposium on Breast Diseases of Inland São Paulo (SIMIP), addressing critical controversies in treatment. Methods: Priority topics were discussed in evidence-based lectures, followed by technical debates and anonymous electronic voting among 110 panelists. Consensus was defined as agreement of ≥75%. Panelists were predominantly mastologists (101), of whom 94 were from São Paulo (Southeast) and seven from other regions: one from Bahia (Northeast), two from Rio Grande do Sul (South), one from Minas Gerais, two from Goiás (Central-West), and one from Ceará (Northeast). The panel also included six oncologists, two pathologists, and one radiotherapist, all from São Paulo. Panelists disclosed no relevant conflicts of interest related to human epidermal growth factor receptor 2 (HER2)-targeted therapies. Lectures were based on selected literature from existing clinical practice guidelines and pivotal clinical trials; no prior systematic review was conducted. The number of respondents varied across questions because voting participation was optional for each item, and the exact number of votes for each question was presented in the respective results tables. The questionnaire consisted of single-choice, forced-response items using binary or categorical formats, depending on the topic (not a Likert scale). The consensus process followed a structured expert panel methodology with anonymous electronic voting, but the number of respondents per question could vary. Results: The majority of respondents (64%) concluded that there is no standardization for HER2-low and ultra-low categories. For adjuvant therapy, 67% defined >5 mm (starting at T1bN0) as the threshold for indication. Neoadjuvant chemotherapy was recommended for tumors ≥2 cm by 68% of specialists. The HER2 genomic/prognosis test (DX) does not significantly alter management, according to 55% of votes. Conclusions: These expert consensus statements reflect current evidence and the majority views of the panel, supporting the management of HER2-positive breast cancer, with emphasis on multidisciplinary evaluation. Standardization of HER2-low and ultra-low categories and the clinical utility of HER2DX require further validation. These statements represent the majority opinion of Brazilian specialists and are intended to support clinical reasoning rather than define mandatory protocols or formal clinical practice guidelines.