Background: HER2-low expression and TILs impacts on clinical features and prognosis in early-stage triple-negative breast cancer (TNBC) remain unclear. Our aim was to evaluate its prognostic value and correlation with clinicopathological characteristics in this population.

Method: A retrospective study of 126 patients with early-stage TNBC who did not undergo neoadjuvant systemic therapy in Vietnam National Cancer hospital from January 2018 to December 2019, HER2 expression was evaluated using the 2018 ASCO/CAP guidelines, Tumor-infiltrating lymphocyte scores (TILs) assessment were assessed based on the guide of an international TILs research group in 2014, using 40% as the cut-off.

Results: Among the 126 patients, with a median age of 54,7±11,4 years, 74,6% were HER2-0 and 25,4% were HER2-low. Compared to HER2-0 tumors, HER2-low tumors were associated with higher age (p=0,02), lower Ki67 score (p=0,05), and lower tumor-infiltrating lymphocyte (p=0,005). During a median follow-up of 54 months, the univariate analysis revealed that patients with HER2-low tumors had a worse overall survival (OS) compared to those with HER2-0 tumors (83,3% vs, 69,6%, p=0,04). However, in the multivariate analysis, HER2 expression did not show a significant association with OS. Instead, independent predictors of OS were identified as tumor-infiltrating lymphocyte scores scores (TILs) (p=0,02; HR=0,17; 95%CI 0,04-0,77) and node status (p=0,002; HR=3,8; 95%CI 1,6-9,1).

Conclusion: This study suggests that HER2-low expression are associated with a lower immune response and worse survival outcome in early-stage TNBC patients compared to HER2-0 tumors. Further investigations is needed to explore the potential of more refined classification and novel strategies that may improve the prognosis for HER2-low TNBC patients.

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