Do all multi-peak LED light-curing units emit similar light outputs?

Triple-negative breast cancer (TNBC) is an aggressive disease characterized by poor prognosis and marked biological heterogeneity. Recently, the classification of HER2-low tumors has emerged as a potential therapeutic target; however, the clinical and biological significance of HER2-low TNBC remains unclear. We retrospectively analyzed 195 patients with primary TNBC at our institution between April 2014 and May 2023. Clinicopathological data, including histological subtype, androgen receptor (AR) expression, BRCA mutation status, Ki-67 index, EGFR, CK5/6, nuclear grade, and treatment response were collected. Tumor-infiltrating lymphocytes (TILs) and PD-L1 expression were additionally assessed in available biopsy samples. Patients were classified into HER2-low (IHC 1+ or IHC 2+ and FISH negative) and HER2-zero (IHC 0) groups. Among 195 TNBC cases, 74 (38%) were HER2-low and 121 (62%) HER2-zero. HER2-low tumors demonstrated higher rates of apocrine carcinoma (32% vs. 15%) and AR positivity (50% vs. 20%). Conversely, HER2-zero tumors exhibited a higher prevalence of BRCA mutations (36% vs. 15%), elevated Ki-67 (69% vs. 54%), and increased PDL1 positivity (63% vs. 44%). TILs correlated with PD-L1 but not with HER2 status. Pathological complete response (pCR) rates after neoadjuvant chemotherapy were similar between groups. HER2-low and HER2-zero TNBC represent biologically distinct subgroups. HER2-low tumors are enriched for luminal AR–like characteristics, while HER2-zero tumors exhibit basal-like, highly proliferative, and immunogenic features. Although treatment outcomes did not differ significantly, these findings suggest that HER2-low and HER2- zero TNBC may require different therapeutic approaches. Prospective studies are warranted to validate these findings and further explore tailored treatment strategies.