Prevalence of her2 low breast cancer in a south Brazilian reference hospital – a real world data base

Background: The effectiveness of targeted therapy for HER2-low breast cancer is an area of ongoing research. Understanding the prevalence of HER2-low is important for identifying patients likely to benefit from these therapies, optimizing treatment and guiding future research. In a referral hospital in southern Brazil, where many breast cancer patients are treated annually, knowing the prevalence of HER2-low in this population provides valuable insights.

Methods: We conducted a retrospective review of breast cancer cases treated in 2020 at a reference hospital in southern Brazil. The study aimed to assess the prevalence of HER2-low breast cancer by analyzing patients with HER2-negative and HER2-low status on immunohistochemistry (IHC), excluding HER2-positive cases. Pathology reports and medical records from an electronic database were reviewed, and clinical and pathological findings were described by frequencies. HER2-low was defined as IHC +1 or +2 with negative in situ hybridization (ISH). The study was approved by the Institutional Review Board.

Results: Of 324 breast cancer cases diagnosed in 2020, 197 were HER2 0 and HER2-low tumors (IHC 1+ or 2+ not amplified). The median age was 58.5 years (range 33-87). Of the HER2-low tumors, 89.65% were hormone receptor-positive, compared to 83.92% of HER2 0 tumors. Stage distribution was 39.5% stage I, 42.13% stage II, 15.22% stage III, and 3.04% stage IV. The prevalence of HER2-low tumors was 14.72% (29 cases), lower than recent trials.

Conclusions: The 14.72% prevalence of HER2-low tumors in our study is lower than in recent trials, underscoring the need for extended research to confirm these findings. Understanding HER2-low prevalence is vital for the Brazilian population, especially given emerging therapeutic options for this subgroup.

Corresponding author: Gabriel Ben Bordinhão (e-mail: gabriel.bordinhao@ufcspa.edu.br).