HER2-Low Breast Cancer: Current Landscape and Future Prospects

Patterns of treatment and outcomes of patients with metastatic HER2-low breast cancer treated with CDK4/6 inhibitors and hormone therapy

Background

The 2018 American Society of Clinical Oncology/College of American Pathologists guidelines classified immunohistochemistry (IHC) 1+ or 2+, FISH-negative breast cancer as HER2-low. To date, only a few studies have investigated the role of HER2-low status in patients with hormone receptor positive/HER2- (HR+/HER2-) metastatic breast cancer (MBC) during CDK4/6 inhibitor (CDK4/6i) therapy.

Methods

This is a multicentre, retrospective cohort study analysing data from patients with HR+/HER2-low and HR+/HER2-0 MBC treated with CDK4/6i as first-line or second-line therapy at the Oncology Units of IRCCS San Matteo Hospital and ICS Maugeri IRCCS in Pavia, Italy, from January 2017 to October 2023. The aim was to assess the activity and effectiveness of CDK4/6i in a real-life setting.

Results

Of the 241 patients included, 240 (99.6%) were women. The median age at diagnosis was 57 years (IQR 48-65 years). Most patients had pM M0 (70.5%). At presentation, 112 (46.5%) had HER2-low and 129 (53.5%) had HER2-0 status. CDK4/6i were administered as first-line therapy in 89.2% of patients and as second-line therapy in 10.8% of patients, with palbociclib (61.4%) being the most common. The median progression-free survival during CDK4/6i therapy was 36.3 months (95% CI 23.6 months to not reached), while the median overall survival was 60.5 months (95% CI 54.4 months to not reached). Progression-free survival differed significantly between palbociclib and abemaciclib/ribociclib (24.4 versus 53.7 months; p=0.0109) and between first-line and second-line therapy (40.5 versus 21.2 months; p=0.0466).

Conclusion

CDK4/6i are effective in both HER2-low and HER2-0 MBC, with HER2-low potentially benefiting more from first-line therapy.

Development and clinical evaluation of [68Ga]Ga-NODAGA-ADAPT6 as a novel HER2-targeted PET radiotracer for breast cancer imaging and treatment monitoring

PURPOSE

Accurate assessment of human epidermal growth factor receptor type 2 (HER2) expression is crucial for diagnosis, treatment planning, and monitoring of breast cancer patients. A 68Ga-labeled tracer based on the albumin-binding domain-derived affinity protein 6 (ADAPT6) was developed to evaluate HER2 expression in breast cancer.

METHODS

The gene encoding ADAPT6 was modified with N-terminal (GHEHEHEDANS) and C-terminal (GSSC) extensions to enhance its functionality. The precursor was synthesized, purified, and characterized, followed by radiolabeling with 68Ga to produce [68Ga]Ga-NODAGA-ADAPT6. In vivo metabolism and biodistribution studies were performed in HCC1954 (HER2-positive) and MDA-MB-468 (HER2-negative) tumor-bearing mice. Additionally, with ethical approval and informed consent, 22 breast cancer patients underwent [68Ga]Ga-NODAGA-ADAPT6 PET imaging to assess HER2 expression in primary and metastatic lesions.

RESULTS

The tracer was prepared with a radiochemical purity exceeding 99% and demonstrated high stability in vivo. Micro-PET/CT imaging revealed significant accumulation of the radiotracer in HCC1954 tumors, which was markedly reduced after HER2 blockade with trastuzumab. In contrast, MDA-MB-468 tumors showed minimal uptake. In the clinical study, [68Ga]Ga-NODAGA-ADAPT6 PET images displayed varying levels of radiotracer uptake in primary and metastatic lesions, which correlated well with the HER2 expression status determined by pathological analysis.

CONCLUSION

[68Ga]Ga-NODAGA-ADAPT6 exhibited excellent pharmacokinetic properties and high specificity for HER2-expressing lesions in PET imaging. These findings highlight its potential as a promising tool for distinguishing different levels of HER2 expression in breast cancer, aiding in personalized treatment strategies.

Redefining therapeutic landscapes: clinicopathological insights into low and ultra-low HER2 expression in male breast cancer

OBJECTIVE

With the emergence of new antibody coupled drugs, the treatment decisions of patients with low and ultra-low HER2 expression have been reshaped. However, the epidemiological characteristics of relatively rare male breast cancer are still unclear. This study discusses the clinicopathological and immunophenotypic characteristics of male invasive breast cancer with low and ultra-low HER2 expression.

METHODS

The clinicopathological and immunophenotypic features of 106 cases of male invasive breast cancer were retrospectively analyzed. HER2 was evaluated according to ASCO/CAP guidelines. The cutoff value of HER2 positive cell staining was > 10%. HER2 negative cases were divided into HER2 low expression (IHC = 1+/2 + and ISH without amplification) and HER2-0 (IHC-0, HER2 null and < 10% weak staining of cell membrane). The clinicopathological characteristics and prognosis of the cases were collected.

RESULTS

106 male patients with invasive breast cancer from 2015 to 2024 were included in this study, and more than 85% of male breast cancer histological types were invasive ductal carcinoma. Immunophenotype: There were 23 cases of HER2-zero (including 13 cases of HER2 ultra-low), 72 cases of HER2 low, 11 cases of HER2 positive, and the HER2 positive rate was 10.38%, and the incidence of low expression was 67.93%; The incidence of HER2 low in male breast cancer was significantly higher than that in female breast cancer, and the difference was statistically significant (P < 0.05). In terms of prognosis, there was no statistical difference between HER2 low male breast cancer and female breast cancer (P > 0.05). There was no statistical difference in survival prognosis between different HER2 status in the male breast cancer cohort.

CONCLUSION

Male invasive breast cancer is rare, and it is more common in the elderly over 60 years old. The positive rate of ER and PR is high, and the incidence of HER2 low is high. The high HER2 low expression rate of male breast cancer can provide a new anti-HER2 treatment decision.

Advanced and Metastatic Triple Negative Breast Cancer-Potential New Treatment

Globally, breast cancer is both the most common cancer and the most common cause of death related to cancer among women. It is estimated that over 2 million women were diagnosed with breast cancer in 2022 worldwide, while almost 400,000 were diagnosed in the EU. Breast cancer has different histopathological subtypes that require different therapeutic approaches. Triple-negative breast cancer (TNBC) is a type that is considered more aggressive; it occurs in about 10 to 20% of all breast cancer cases. Approximately 40% of women initially diagnosed with TNBC will develop metastases. The objective of this study is to present current clinical trials focused on new treatment of advanced and metastatic TNBC. The study was conducted by searching the clinicaltrials.gov database. Due to the scope of this paper, primary endpoints in the included studies were objective response rate, treatment-emergent adverse events or serious adverse events, progression-free survival, and probability of pathologic complete response. Some of the selected studies were phase I or II RCTs; therefore, we should carefully examine their future results and implications for clinical guidelines.

Molecular Subtypes and Mechanisms of Breast Cancer: Precision Medicine Approaches for Targeted Therapies

Breast cancer remains one of the most prevalent diseases worldwide, primarily affecting women. Its heterogeneous nature poses a significant challenge in the development of effective and targeted treatments. Molecular characterization has enabled breast cancer to be classified into four main subtypes: luminal A, luminal B, HER2-positive, and triple-negative breast cancer, based on hormone receptor expression and HER2 status. A deeper understanding of these molecular markers and their associated signaling pathways, such as MAPK and PI3K/AKT, is essential for improving prognosis and optimizing treatment strategies. Currently, several therapeutic agents are utilized in neoadjuvant and adjuvant therapies, often in combination with surgical interventions. However, emerging evidence highlights the growing challenge of drug resistance, which significantly limits the efficacy of existing treatments. Addressing this issue may require innovative approaches, including combination therapies and precision medicine strategies, tailored to the molecular profile of each patient. Therefore, a comprehensive understanding of the pathophysiologic mechanisms driving breast cancer progression and resistance is crucial for the development of advanced targeted therapies with greater precision and efficacy. This review aims to explore recent advancements in molecular research related to breast cancer subtypes and provide a critical analysis of current therapeutic approaches within the framework of precision medicine.

Pathologic response rates in HER2-low versus HER2-zero early breast cancer patients receiving neoadjuvant therapy: a systematic review and meta-analysis

BACKGROUND

Currently, the primary methods for detecting HER2 expression levels are immunohistochemistry (IHC) and in situ hybridization (ISH), with the traditional standard being a HER2-positive score of 3 + accompanied by ERBB2 gene amplification detected through ISH. However, a new entity has recently emerged: HER2-low, defined as HER2 IHC 1 + or 2 + with negative ISH. HER2-low breast cancer, representing 45-60% of all HER2-negative tumors, has distinct biological characteristics and uncertain responses to conventional HER2-targeted therapies. Recent studies suggest varied clinical outcomes, highlighting the need for further investigation into the impact of HER2-low status on treatment efficacy and prognosis.

OBJECTIVE

This meta-analysis evaluates the difference in complete pathological response (pCR), disease-free survival (DFS), and overall survival (OS) between HER2-low and HER2-zero phenotypes.

METHODS

We systematically searched the main databases PubMed, Scopus, and Web of Science for articles evaluating women in neoadjuvant therapy expressing HER2-low and HER2-zero. We computed odds ratios (ORs) or hazard ratios (HRs) using DerSimonian and Laird random-effect models for all endpoints, with 95% confidence intervals (CIs). We assessed the heterogeneity using I2 statistics. R, version 4.2.3, was used for statistical analyses.

RESULTS

38 studies totaling 70,104 patients were included. The HER2-low group accounted for 61.3% of patients while HR + status represented 52.4% in the whole research. In 67,839 women, the pCR was analyzed, which in the overall cohort analysis favored the HER2-zero group (OR 0.84; 95% CI 0.78-0.90; p = 0.000005; I2 = 15%). Subgroup analyses for triple-negative breast cancer (TNBC) and HR + patients also favored HER2-zero expression, with an OR of 0.91 (95% CI 0.83-1.0; p < 0.041; I2 = 12%) and 0.75 (95% CI 0.70-0.81; p < 0.000001; I2 = 0%), respectively. In the multivariate analysis across all patients, both DFS and OS outcomes were significantly favorable for the HER2-low expression group, with HR 0.8317 (95% CI 0.7036-0.9832; p = 0.031) for DFS and HR 0.806 (95% CI 0.663-0.979; p = 0.03) for OS.

CONCLUSION

Based on our findings, HER2-zero status is associated with a significantly higher pathological complete response (pCR) rate compared to HER2-low in early-stage breast cancer, and other survival outcomes. These results suggest that HER2-zero should be considered a prognostic factor in early-stage breast cancer and taken into account in neoadjuvant treatment planning and future clinical research.

A multifunctional Pt/DMSN nanozyme-based colorimetric-fluorescence sensing platform for breast cancer detection

Nanozyme-linked immunosorbent assay has emerged as a promising strategy for sensitive biosensing. However, the catalytic activity and stability of nanozymes affect the accuracy of immunosorbent assays. In this study, we synthesized a Pt/DMSN nanozyme with peroxidase-mimicking activity, which effectively catalyzed the oxidation of peroxidase substrate 3,3',5,5'-tetramethylbenzidin (TMB) in the presence of hydrogen peroxide. Capitalizing on its peroxidase-like activity, the Pt/DMSN nanozyme was functionalized with dual-fluorescent recognition elements (HER2-mAbs and sk6Ea aptamers) to establish a nanozyme-linked immunosorbent assay platform, which exhibited catalytic stability and substrate affinity comparable to horseradish peroxidase. The resulting Multi-Pt/DMSN platform was used to selectively distinguish HER2-positive breast cancer cells from luminal A, triple-negative breast cancer subtypes, and non-neoplastic cells, achieving a detection limit of 50 HER2-positive cells within 30 min. The combination of robust enzyme-like activity and tumor-targeting properties enables fluorescence imaging, providing dual-mode diagnostic functionality. This work presents a prospective platform for differentiating breast cancer subtypes in early diagnosis.

Advances in Ultrasound-Targeted Microbubble Destruction (UTMD) for Breast Cancer Therapy

Breast cancer is one of the most common types of cancer in women worldwide and is a leading cause of cancer deaths among women. As a result, various treatments have been developed to combat this disease. Breast cancer treatment varies based on its stage and type of pathology. Among the therapeutic options, ultrasound has been employed to assist in the treatment of breast cancer, including radiation therapy, chemotherapy, targeted immunotherapy, hormonal therapy, and, more recently, radiofrequency ablation for early-stage and inoperable patients. One notable advancement is ultrasound-targeted microbubble destruction (UTMD), which is gradually becoming a highly effective and non-invasive anti-tumor modality. This technique can enhance chemical, genetic, immune, and anti-vascular therapies through its physical and biological effects. Specifically, UTMD improves drug transfer efficiency and destroys tumor neovascularization while reducing toxic side effects on the body during tumor treatment. Given these developments, the application of ultrasound-assisted therapy to breast cancer has gained significant attention from research scholars. In this review, we will discuss the development of various therapeutic modalities for breast cancer and, importantly, highlight the application of ultrasound microbubble-targeted disruption techniques in breast cancer treatment.

Novel Molecular Classification of Breast Cancer with PET Imaging

Breast cancer is a heterogeneous disease characterized by a wide range of biomarker expressions, resulting in varied progression, behavior, and prognosis. While traditional biopsy-based molecular classification is the gold standard, it is invasive and limited in capturing tumor heterogeneity, especially in deep or metastatic lesions. Molecular imaging, particularly positron emission tomography (PET) imaging, offering a non-invasive alternative, potentially plays a crucial role in the classification and management of breast cancer by providing detailed information about tumor location, heterogeneity, and progression. This narrative review, which focuses on both clinical patients and preclinical studies, explores the latest advancements in PET imaging for breast cancer, emphasizing the development of new tracers targeting hormone receptors such as the estrogen alpha receptor, progesterone receptor, androgen receptor, estrogen beta receptor, as well as the ErbB family of receptors, VEGF/VEGFR, PARP1, PD-L1, and markers for indirectly assessing Ki-67. These innovative radiopharmaceuticals have the potential to guide personalized treatment approaches based on the unique tumor profiles of individual patients. Additionally, they may improve the assessment of treatment efficacy, ultimately leading to better outcomes for those diagnosed with breast cancer.

Antibody-drug conjugates in patients with advanced/metastatic HER2-low-expressing breast cancer: a systematic review and meta-analysis

Background

Until recently, targeted therapies have failed to benefit patients with human epidermal growth factor receptor 2 (HER2)-low-expressing breast cancer (BC). Nevertheless, antibody-drug conjugates (ADCs) have reshaped their prognosis.

Objectives

We performed a systematic review and meta-analysis to assess the effectiveness of ADCs in patients with HER2-low advanced/metastatic (a/m) BC.

Design

This study is a systematic review and meta-analysis.

Data sources

We searched PubMed, Embase, and Cochrane databases as well as the American Society of Clinical Oncology, European Society for Medical Oncology, and San Antonio Breast Cancer Symposium conference proceedings.

Methods

Studies evaluating ADCs (trastuzumab deruxtecan (T-DXd), sacituzumab govitecan (SG), MRG002, and RC48-ADC) in patients with HER2-low a/mBC were included. We used R software (v.4.2.2) and random effects models for all analyses. Heterogeneity was assessed using the I 2 test.

Results

Overall, 14 studies were included (five real-world studies and nine clinical trials (CTs)), with 2883 HER2-low a/mBC patients: 808 received treatment of physician's choice (TPC), and 2075 ADCs. Most were treated with T-DXd (n = 1691), followed by SG (n = 310), MRG002 (n = 56), and RC48-ADC (n = 18). Patients treated with T-DXd achieved a significantly higher objective response rate (ORR), disease control rate (DCR), and clinical benefit rate (CBR) than those receiving other ADCs. In the pooled analysis of four randomized CTs, ADCs statistically prolonged progression-free survival (n = 1828, hazard ratio (HR) 0.50, 95% confidence interval (CI) 0.36-0.68, I 2 = 82%, p < 0.001) and overall survival (n = 1546, HR 0.70, 95% CI 0.57-0.86, I 2 = 43%, p < 0.001) compared with TPC. Patients on ADCs also achieved a greater antitumor response than TPC, including better ORR (odds ratio (OR), 3.7, 95% CI 2.5-5.6, I 2 = 59%, p < 0.001), DCR (OR, 2.7, 95% CI 2.1-3.5, I 2 = 0%, p < 0.001), and CBR (OR, 3.6, 95% CI 2.6-5.2, I 2 = 56%, p < 0.01).

Conclusion

Our systematic review and meta-analysis confirms the efficacy of ADCs in HER2-low a/m BC patients over TPC. Future studies should focus on bringing ADCs into earlier lines of therapy in this population.

Trial registration

This study was registered in PROSPERO (CRD42024452962).

Unfavorable Prognostic Impact of HER2 2+/FISH-Negativity in Older Patients with HER2-Negative and High-Risk Breast Cancer

Purpose

Human epidermal growth factor receptor 2 (HER2)-low breast cancer, consisted of carcinomas with HER2 protein 1+ or 2+ without gene amplification, has been considered a biologically heterogeneous disease. Limited research separately investigated the prognostic significance of HER2 2+ without gene amplification, and no evidence can be identified in older patients. In this dedicated cohort of older patients with HER2-negative and high-risk breast cancer, we analyzed the real-world prognosis after standard adjuvant chemotherapy, and investigated the associations of survival with HER2 2+ without gene amplification.

Patients and Methods

From January 2016 to December 2021, older patients (≥65 years) with breast cancer were reviewed, and HER2-negative/high-risk disease receiving standard adjuvant chemotherapy was included. HER2-negativity was defined as immunohistochemistry (IHC) score 0, 1+ or 2+ without gene amplification by fluorescent in situ hybridization (FISH). Cox proportional hazards regression analyses were performed to assess the associations of HER2 2+/FISH-negativity with disease-free survival (DFS), which was estimated by the Kaplan-Meier method and compared by the Log rank test.

Results

This cohort consisted of 121 consecutive older patients. With a median follow-up of 46 months, 12 patients had a DFS event. By univariate and multivariate analyses, HER2 2+/FISH-negativity was the only independent predictor for worse DFS (hazard ratio 5.56; P=0.046). Patients with HER2 2+/FISH-negativity had significantly poorer DFS compared with those with HER2 0 or 1+ (Log rank test, P=0.029). In both hormone receptor (HR)-positive (Log rank test, P=0.052) and HR-negative (Log rank test, P=0.125) subgroups, HER2 2+/FISH-negativity showed a marginally significant adverse influence on DFS.

Conclusion

In older patients with HER2-negative/high-risk breast cancer undergoing standard adjuvant chemotherapy, our findings suggest that HER2 2+/FISH-negativity has an independent negative impact on prognosis.

Prognostic Impact of HER2 Low Status in Male Breast Cancer: Prospective Cohort Analysis

BACKGROUND

Male breast cancer (MBC) is a rare disease, and the potential influence of low expression of human epidermal growth factor receptor 2 (HER2 low) remains unexplored.

METHODS

In this prospective cohort study, we evaluated 870 patients treated for MBC between May 2009 and June 2023 to assess HER2 low status and its prognostic implications.

RESULTS

With a median follow-up of 43 months (range 1-175 months), 659 eligible patients were categorized into three groups based on HER2 status: 501 (76%) HER2 low, 81 (12.3%) HER2 zero, and 77 (11.7%) HER2 positive. HER2 positivity correlated with younger age, higher proliferation index, non-specific type histology, lymphovascular invasion (LVSI), and low differentiation grade. Notably, all these parameters were equally distributed between the HER2 zero and HER2 low groups. Additionally, HER2 positivity was significantly associated with increased occurrences of regional and distant lymph nodes and pulmonary metastases. However, no statistically significant difference was observed between HER2 zero and HER2 low. Disease-free and overall survival showed no significant disparities between the groups.

CONCLUSIONS

Our findings suggest that HER2 low status is frequently detected in MBC. Despite this, HER2 low did not correlate with clinical and pathological parameters, nor did it impact patients' survival.

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

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.

Comprehensive Assessment of Immune Phenotype and Its Effects on Survival Outcomes in HER2-Low versus HER2-Zero Breast Cancer

Background

The understanding of molecular characteristics of HER2-low breast cancer is evolving since the establishment of trastuzumab deruxtecan. Here, we explore the differences in expression patterns of immune-related genes in the tumor immune microenvironment (TME) and survival between HER2-low and HER2-zero breast cancers.

Methods

Comprehensive genomic and immune profiling, including RNA-seq gene expression assessment of 395 immune genes, was performed on FFPE samples from 129 patients with advanced HER2-negative (immunohistochemistry (IHC) 0, 1+ or 2+ with negative ERBB2 amplification by in-situ hybridization) breast cancer. Both estrogen receptor (ER) and HER2 statuses were obtained from available pathology reports. mRNA expressions of immune biomarkers, except for PD-L1 IHC and TMB, were derived from RNA-seq. Statistical comparisons were performed using the Kruskal-Wallis or Wilcoxon Rank-Sum test or the two-sample test for equality of proportions with continuity correction (p≤0.05 for significance). Survival differences were calculated using Kaplan-Meier analysis (p≤0.05 for significance).

Results

There were no significant differences in mRNA expressions of immune-related genes between HER2-low and HER2-zero breast cancers. However, HER2-low breast cancers were associated with a higher proportion of ER-positivity. When ER was analyzed along with HER2, we observed a significantly higher tumor immunogenic signature (TIGS) expression in HER2-zero/ER-negative tumors than in HER2-low/ER-positive tumors (p=0.0088). Similarly, lower expression of PD-L1 and T cell immunoglobulin and ITIM domain (TIGIT) mRNA was observed in HER2-low/ER-positive tumors when compared to HER2-zero/ER-negative tumors (p=0.014 and 0.012, respectively). Patients with HER2-low tumors had a longer median OS than those with HER2-zero tumors (94 months vs 42 months, p=0.0044).

Conclusion

Patients with HER2-low breast cancer have longer survivals yet display no differences in immune-related gene expression when compared to those with HER2-zero cancers. The differences in survival can be attributed to the higher rate of ER-positivity seen in HER2-low breast cancers, compared to HER2-zero tumors.

Application Value of Music Therapy in Improving the Emotional State and Quality of Life of Hospitalized Patients with Breast Cancer: Retrospective Study

OBJECTIVE

This study aimed to apply music therapy as a clinical treatment for patients with breast cancer (BC) experiencing mild or moderate depression during hospitalization and observe any improvements in their depression and quality of life.

METHODS

A total of 102 patients who had mild-to-moderate depression, were diagnosed with BC, and were admitted to our hospital from October 2022 to October 2023 were selected as the subjects of a retrospective analysis. According to their participation in short-term music therapy, they were divided into a control group (routine nursing treatment n = 45) and an observation group (routine nursing treatment + music therapy n = 57). Self-rating depression (SDS) scale and functional assessment of cancer therapy-breast (FACT-B) scale Chinese version 4.0 scores and patient satisfaction after treatment were compared between the two groups.

RESULTS

After treatment, the SDS scale scores and FACT-B scores of the observation group were significantly better than those of the control group (P < 0.001). The patient satisfaction in the observation group was higher than in the control group (P < 0.05).

CONCLUSION

Music therapy is a highly safe method to improve the depression and quality of life of patients with BC. It also provides a simple and convenient nondrug clinical treatment with broad application prospects.

Analyzing Neoadjuvant Chemotherapy Effects in HER2-Low Breast Cancer: Real World Data

PURPOSE

Neoadjuvant chemotherapy (NAC) can be used as upfront therapy in aggressive breast cancer (BC). human epidermal growth factor receptor 2 (HER2)-low BC, defined as tumors scoring +1 or +2 on immunohistochemistry without HER2 gene amplification by in situ hybridization, lacks information on real-world data (RWD) outcomes, especially in the NAC setting. This subgroup, which does not reach the HER2 positive criteria due to its lower receptor expression, represents a distinct clinical category potentially requiring tailored therapeutic approaches.

STUDY OBJECTIVE

 The objective of this study is to characterize patients with BC with HER2-low status who received NAC in a Brazilian public reference center for female tumors and key outcomes such as pathological complete response (pCR), overall survival (OS), and metastasis-free survival (MFS).

METHODS

A retrospective cohort study based on a large BC database from a reference cancer center in Brazil. Patients with BC that received NAC, diagnosed between 2011 and 2020, were included if they presented HER2-low status (defined as tumors scoring +1 or +2 on immunohistochemistry without HER2 gene amplification by in situ hybridization) and had complete data on outcomes. Clinical and demographic data were collected, such as age, menopausal status, Ki-67, hormone receptor expression and others. Key outcomes from the study comprised pCR (defined as ypT0/TIs/ypN0), overall survival, and metastasis-free survival (MFS). Survival analyses were conducted through the semiparametric Kaplan-Meier method to assess OS and MFS by pCR status, considering BC diagnosis as the index date.

RESULTS

Overall, 297 patients were eligible and 141 were included in the study after matching the HER2-low definition. The pCR was seen in 18 out of 141 patients (12.7%). The median overall survival was 8.2 years, and the median MFS was 2.7 years. The OS of pCR was 83.4% and non-pCR was 58.1%; the DFS of pCR was 55.5% and non-pCR 40.6%.

CONCLUSION

This study gives updated insights on pCR, OS, and MFS in women with HER2-low BC exposed to NAC.