Characterization of real-world clinical and pathological differences between HER2-0 and HER2-low localized breast cancer.

Compared to HER2-0, HER2-low patients had fewer comorbidities (p = 0.030) and were more often diagnosed asymptomatically via screening (p = 0.012).

HER2-low tumors exhibited lower histological grade (p = 0.021), higher hormone receptor (HR) expression levels (ER: p = 0.0003; PR: p = 0.001) and lower proliferation rates (p = 0.005) than HER2-0 tumors.

In HR+ patients, HER2-low was associated with superior OS in stage 2 (p = 0.028) and stage 2a disease (p = 0.004), as well as in patients with 1-2 metastatic lymph nodes (OS: p = 0.006, DFS: p = 0.044).