Background: Trastuzumab (Herceptin) is the key systemic therapy for HER2-positive breast cancer. However, the initial response rate is limited to approximately 50% in patients. Moreover, most patients, especially at an advanced stage, eventually develop acquired resistance. Understanding the mechanisms of trastuzumab resistance is crucial for achieving better treatment outcome in this group of patients. Methods: A trastuzumab-resistant (TR) cell line was developed using the BT474 HER2-positive breast cancer cell line. Whole-transcriptome expression array was performed and the TR-related gene NDUFA4L2 was identified by differential expression analysis between BT474 and BT474-TR. Mitochondrial localization of NDUFA4L2 was confirmed by immunofluorescence and western blotting using mitochondrial fractionation. Mitochondrial function and energy metabolism were evaluated using Seahorse, ATP production, and lactate production assays, and cellular reactive oxygen species (ROS) levels were determined using DCFDA. NDUFA4L2 expression in patients was evaluated by immunohistochemistry, and relapse-free survival was analyzed using the Kaplan–Meier method. Results: NDUFA4L2 was highly expressed in the TR HER2-positive breast cancer cell line. High expression level of NDUFA4L2 was associated with shorter relapse-free intervals in trastuzumab-treated HER2-positive breast cancer patients. Overexpression of NDUFA4L2 enhanced Warburg effects, enhanced aerobic glycolysis, reduced oxygen consumption, and lowered ROS production. Mechanistically, overexpression of NDUFA4L2 facilitated mitochondrial relocalization of HER2 and suppressed ROS production, thus rendering cancer cells more resistant to trastuzumab treatment. Conclusions: We identified NDUFA4L2 as a new biomarker and potential therapeutic target for TR HER2-positive breast cancer.

Objective: To evaluate the efficacy and safety of anlotinib-based treatment in metastatic breast cancer (MBC) patients with failure of standard treatment.Methods: We collected the medical data of 56 female patients with the diagnosis of MBC and had failed the standard treatment before. These patients received at least two cycles of anlotinib-based treatment as the second-line or beyond treatment between October 2019 and April 2022 in Jiangsu Cancer Hospital. The primary endpoint of our study was progression-free survival (PFS), and it was estimated with Kaplan-Meier. The second end points were disease control rate (DCR), objective response rate (ORR), and side effects.Results: The median PFS time of a total of 56 patients was 5.7 months (95% CI, 3.17-8.23 months). The ORR and DCR was 28.6% and 71.4%, respectively. In second-line, third-line, and beyond treatment, the median PFS was 11.7 months, 8.7 months, and 4.7 months, respectively. In different subtype of breast cancer, the median PFS was 5.6 months, 5.7months, and 6.4 months in human epidermal growth factor receptor 2 positive (HER2+), hormone receptor positive and HER2 negative (HR+/HER2-), and triple negative breast cancer (TNBC) patients, respectively. Most adverse effects were clinically manageable, and the most common events were platelet count decrease (35.7%), hand-foot syndrome (19.6%), diarrhea (19.6%), and fatigue (17.9%). The most common grade 3 and 4 adverse events were platelet count decrease (10.7%), diarrhea (7.1%), and oral mucositis (5.4%).Conclusion: Anlotinib-based treatment showed good efficacy and manageable toxicity in multi-line treatment of MBC patients who failed the standard treatment.

Purpose: This study aimed to investigate the possibility of UCP-2 inhibitor in reducing acquired resistance of trastuzumab to improve the outcome of patients receiving trastuzumab therapy by exploring the relationship between UCP-2 expression and HER2 signaling pathway and examining whether UCP-2 expression was modulated by trastuzumab treatment. Methods: 32 women diagnosed with primary HER2-positive breast cancer were recruited in this study. Needle biopsy was obtained from patients before they received at least four cycles neoadjuvant therapy containing trastuzumab in combination with chemotherapy. Surgical tumor biopsy was obtained during surgical procedure after the neoadjuvant therapy. Levels of HER2 phosphorylation and UCP-2 expression were detected by immunohistochemistry (IHC) and compared between tumor needle biopsy tissue and surgical tumor samples of these patients, as well as in BT474 breast cancer cells before and after trastuzumab treatment. HER2-selective phosphorylation/kinase activity inhibitor ONT-380 was used to identify the correlation between HER2 phosphorylation level and UCP-2 expression. UCP-2 inhibitor Genipin was then used to evaluate the apoptosis index in BT474 cells treated with trastuzumab. Results: UCP-2 expression was significantly elevated in surgical tumor samples from breast cancer patients receiving trastuzumab in a neoadjuvant setting. We further confirmed our findings in HER2-positive BT474 cell line and found that trastuzumab treatment induced phosphorylation of HER2 and the overexpression of UCP-2, and the latter can be reversed by HER2 selective kinase inhibitor ONT-380. Moreover, UCP-2 inhibitor Genipin significantly enhanced the proliferation suppression effects of trastuzumab and markedly promoted apoptosis. Conclusion: Taken together, our study identified UCP-2 as a novel therapeutic target for HER2 positive breast cancer and UCP-2 inhibitor may have great potential to enhance the response rate and efficacy of trastuzumab therapy.

Disitamab vedotin (RC48-ADC), an antibody-drug conjugate (ADC), combines specific antibody disitamab with cytotoxicity monomethyl auristatin E to effectively target the human epidermal growth factor receptor 2 (HER2) protein on tumor cells for precise elimination. Recent studies have demonstrated that RC48-ADC offers therapeutic benefits for patients with HER2-positive and HER2-low-expression breast cancer (BC). However, a thorough exploration of its efficacy and safety in real-world settings for patients with metastatic breast cancer (mBC) is currently lacking. This retrospective, multicenter, real-world study included patients with mBC who received RC48-ADC from September 2021 to March 2024. These patients include HER2-positive BC and HER2-low-expression BC. The primary endpoint was progression-free survival (PFS). Secondary endpoints included overall survival (OS), restricted mean survival time, objective response rate (ORR), and disease control rate (DCR). Factors affecting efficacy and the occurrence of treatment-related adverse events (TRAE) were evaluated. The study included a cohort of 89 patients with mBC, with 48 of those being identified as HER2-positive. As of March 2024, 22 deaths were recorded, with an immature median OS. Total PFS varied from 1.0 to 31.2 months, with a median of 5.5 months (95% CI, 4.368-6.632). HER2-positive patients exhibited prolonged PFS compared with HER2-low-expression patients (6.6 months vs 4.1 months, P = .023). The overall ORR stood at 25.8% (95% CI, 0.178-0.358), with higher rates observed in HER2-positive patients compared with HER2-low-expression patients (31.3% vs 19.5%). Similarly, the overall DCR was 78.7% (95% CI, 0.691-0.859), with HER2-positive patients demonstrating superior DCR compared with HER2-low-expression patients (83.3% vs 73.2%). Notably, HER2 expression emerged as the primary determinant of RC48-ADC efficacy. The most prevalent TRAE among all patients included leukopenia (21.3%) and alopecia (20.2%). RC48-ADC showcases promising efficacy and manageable safety in patients with both HER2-positive and HER2-low-expression mBC.

Background: In previous clinical trials, pyrotinib has shown good antitumor activity and manageable toxicity in human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC). However, real-world data on pyrotinib remain limited. In this study, we reported the latest real-world data on the efficacy and safety of pyrotinib in HER2-positive MBC. Methods: This multicenter retrospective study included 337 HER2-positive MBC patients treated with pyrotinib between October 2016 and October 2024. We reported the analysis of the efficacy and safety of pyrotinib in HER2-positive MBC. The primary endpoints were progression-free survival (PFS) and overall survival (OS). Results: As of April 1, 2025, the median follow-up duration was 42.6 months (range, 2.0-92.7). The median line of treatment was two. The median PFS was 15.3 months (95% CI, 12.9-17.6). By treatment line, the median PFS was 21.4 months (95% CI, 10.1-32.6) for first-line treatment, 14.8 months (95% CI, 11.4-18.1), and 10.9 months (95% CI, 8.1-13.7) for second-line and third-line or above treatment. The 3-year OS rate was 54.6% overall, with 63.2%, 61.1%, and 37.7% for first-line, second-line, and third-line or above treatment. The ORR, DCR, and CBR were 41.5%, 91.2%, and 80.0%. We further analyzed 57 patients with brain metastases (BM). The result showed that the median duration of response (DoR) and time to response (IQR) of radiotherapy-naïve ones were 12.6 months (95% CI, 6.8-18.4) and 1.7 months (95% CI, 1.3-2.2), respectively. The most frequent grade 3 or 4 adverse event was diarrhea. No treatment-related deaths were reported. Conclusion: The updated analysis demonstrated that pyrotinib could be a promising treatment option in HER2-positive MBC with acceptable toxicity in the real world. Survival is still under assessment with longer follow-up.