Characterization of HER2-Low Breast Tumors among a Cohort of Colombian Women.

Simple Summary: HER2-low breast cancer is a newly recognized subtype that has shown promising responses to treatment with antibody–drug conjugates (ADCs). However, there is still little known about its clinical and molecular characteristics. In this study, we examined the clinical and pathological features, survival rates, and expression of HER2-related genes in Colombian patients with HER2-low breast cancer, comparing them to HER2-negative and positive groups. We found that HER2-low tumors were better differentiated and had a lower proliferation index compared to HER2-positive tumors. Additionally, compared to HER2-negative cases, HER2-low patients had higher mRNA expression of the ERBB2 gene and longer overall survival rates. Despite these findings, there were no significant differences in survival when adjusted for estrogen receptor status and clinical stage. These results highlight the need for further research on HER2-low breast cancer to optimize treatment strategies for this unique group. HER2-low tumors have shown promise in response to antibody–drug conjugates (ADCs) in recent clinical trials, underscoring the need to characterize this group's clinical phenotype. In this study, we aimed to explore the clinicopathological features, survival rates, and HER2 amplicon mRNA expression of women affected with HER2-low breast cancer, compared with HER2-negative and HER2-positive groups. We included 516 breast cancer patients from Colombia, for whom we compared clinicopathological features, mRNA expression of three HER2 amplicon genes (ERBB2, GRB7 and MIEN1), survival and risk of mortality between HER2-low cases (1+ or 2+ with negative in situ hybridization (ISH) result) with HER2-positive (3+ or 2+ with positive ISH test) and HER2-negative (0+) cases. A higher proportion of patients with better-differentiated tumors and a lower proliferation index were observed for HER2-low tumors compared to the HER2-positive group. Additionally, HER2-low tumors showed higher mRNA expression of the ERBB2 gene and longer overall survival rates compared to HER2-negative cases. Nonetheless, a Cox-adjusted model by ER status and clinical stage showed no statistically significant differences between these groups. Our results show differences in important clinicopathological features between HER2-low and both HER2-positive and negative tumors. Given this unique phenotype, it is crucial to evaluate the potential advantages of ADC therapies for this emerging subtype of breast cancer. [ABSTRACT FROM AUTHOR]