New definitions in breast cancer: neoadjuvant chemotherapy response and survival analysis in HER2-Low, HER2-Ultralow, and HER2-Zero groups

Çubukçu S. S., Öztürk Ç., Okcu O.

38th European Congress of Pathology, Stockholm, İsveç, 12 - 16 Eylül 2026, cilt.489, ss.358-359, (Özet Bildiri)

  • Yayın Türü: Bildiri / Özet Bildiri
  • Cilt numarası: 489
  • Doi Numarası: 10.1007/s00428-026-04642-8
  • Basıldığı Şehir: Stockholm
  • Basıldığı Ülke: İsveç
  • Sayfa Sayıları: ss.358-359
  • Recep Tayyip Erdoğan Üniversitesi Adresli: Evet

Özet

Background & Objectives: The aim of this study was to evaluate responses to neoadjuvant chemotherapy (NAC) and survival outcomes in the newly defined HER2-low and HER2-ultralow categories of breast cancer, and to compare these groups with HER2-0 cases. Methods: The study included around 214 cases of invasive breast carcinoma. Between 2014 and 2025, all cases underwent neoadjuvant therapy and surgical resection. The cases were grouped by immunohistochemical (IHC) score into the following categories: HER2-0, HER2-ultralow (IHC 1+), and HER2-low (IHC 2+/ISH negative). Treatment response was measured using Residual Cancer Burden (RCB) scoring and pathological complete response (pCR) rates. Differences in DFS (disease-free survival) and OS (overall survival) between groups were compared statistically. Results: Pathological complete response (pCR) rates were 20.5% in the HER2-ultralow group, 17.9% in the HER2-0 group, and 15.8% in the HER2-low group. No statistically significant difference was observed in pCR rates or RCB classes among these three groups (p > 0.05). In contrast, a significant difference was observed between the HER2- positive (IHC 3+) group and these low-expression groups (p < 0.001). The highest residual disease burden (RCB Class 3) was observed in the HER2-0 group, at 41%. In survival analyses, the mean overall survival times for the HER2-0 (82.3 months), HER2-ultralow (84.1 months), and HER2- low (83.5 months) groups were very similar, with no significant differences among them. Conclusion: Our data indicate that HER2-low and HER2- ultralow breast cancers have a clinical course and chemotherapy sensitivity similar to classic HER2-negative (HER2-0) tumours. No significant heterogeneity was observed among these three subgroups in response to neoadjuvant therapy or in survival. This suggests that current chemotherapy regimens are similarly effective for these patients, but targeted next-generation therapies may help identify potential differences among the groups.