HER2-Low Breast Cancer: Incidence, Clinicopathologic Features, and Survival Outcomes From Real-World Data of a Large Nationwide Cohort

Landscape of HER2-low breast cancer: Insights from a six-year study on prevalence and clinicopathological characteristics

Human epidermal growth factor receptor 2 (HER2)-low breast cancer has emerged as a subtype of breast cancer, defined by HER2 1+/2+ in immunohistochemistry (IHC) and absence of ERBB2 gene amplification on fluorescence in situ hybridization (FISH). Recent trials showed marked response of HER2-low breast cancer to novel anti-HER2 antibody-drug-conjugates. Data on characteristics of HER2-low breast cancer subtype is limited. Real-world data from the Anatomic Pathology Department of Hotel-Dieu de France, spanning 2017-2023, was retrospectively collected. HER2-positive patients were excluded to compare HER2-low to HER2-zero breast cancer subtypes. Clinicopathological characteristics between the groups were compared using a Chi-Squared test. Out of 1195 patients, we observed 341 (28.5 %) HER2-low breast cancers cases. HER2-positive breast cancer cases (n = 178; 14.9 %) were excluded. There was no significant difference in age and sex between HER2-low and HER2-zero group (p = 0.33 and 0.79, respectively). HER2-low breast cancer was associated with positive estrogen receptor status and positive progesterone receptor status (p < 0.001 and p = 0.01, respectively). Ductal adenocarcinomas were more commonly observed in HER2-low group (p < 0.001). When stratified by hormone (HR) status, 87.4 % of patients had HR-positive status and 12.6 % were HR-negative. Among the HR-negative group, HER2-low tumors tended to show lower proliferation index compared to HER2-zero tumors (25%vs.10 %, p = 0.04). This study showed that HER2-low is distinct from HER2-zero and is common among patients with breast cancer. Clinicopathological features such as histological type differ between HER2-zero and HER2-low breast cancer. Within HR-negative breast cancer, those with low HER2 expression exhibit a less aggressive profile compared to HER2-zero tumors.

Best practices for achieving consensus in HER2-low expression in breast cancer: current perspectives from practising pathologists

AIMS

Human epidermal growth factor receptor 2 (HER2) expression is an important biomarker in breast cancer (BC). Most BC cases categorised as HER2-negative (HER2-) express low levels of HER2 [immunohistochemistry (IHC) 1+ or IHC 2+/in-situ hybridisation not amplified (ISH-)] and represent a clinically relevant therapeutic category that is amenable to targeted therapy using a recently approved HER2-directed antibody-drug conjugate. A group of practising pathologists, with expertise in breast pathology and BC biomarker testing, outline best practices and guidance for achieving consensus in HER2 IHC scoring for BC.

METHODS AND RESULTS

The authors describe current knowledge and challenges of IHC testing and scoring of HER2-low expressing BC and provide best practices and guidance for accurate identification of BCs expressing low levels of HER2. These expert pathologists propose an algorithm for assessing HER2 expression with validated IHC assays and incorporate the 2023 American Society of Clinical Oncology and College of American Pathologist guideline update. The authors also provide guidance on when to seek consensus for HER2 IHC scoring, how to incorporate HER2-low into IHC reporting and present examples of HER2 IHC staining, including challenging cases.

CONCLUSIONS

Awareness of BC cases that are negative for HER protein overexpression/gene amplification and the related clinical relevance for targeted therapy highlight the importance of accurate HER2 IHC scoring for optimal treatment selection.

Impact of immunohistochemistry staining conditions on the incidence of human epidermal growth factor receptor 2 (HER2)-low breast cancer

We investigated frequencies of HER2-low breast cancer (BC) (immunohistochemistry [IHC] 1+ or 2+ without gene amplification) before and after IHC conditions were modified in order to understand the impact of IHC staining conditions on frequencies of HER2-low BC. Primary BC cases diagnosed at the Yeungnam University Hospital (YUH, n = 728) or Keimyung University Dongsan Hospital (KUDH, n = 290) in 2022 were reviewed, and data on HER2 status and IHC conditions were collected (cohort 1). Both institutions used the 4B5 antibody for HER2 IHC but had different staining protocols. After modifications of the IHC conditions at both institutions, primary BC cases (YUH, n = 324 and KUDH, n = 135) diagnosed from April to July 2023 (cohort 2) were reviewed to assess any changes in the frequency of HER2 status. In cohort 1, of the 728 cases diagnosed at YUH, 556 (76.4%) were HER2-zero, 76 (10.4%) were HER2-low, and 96 (13.2%) were HER2-positive, and of the 290 cases diagnosed at KUDH, 135 (46.6%) were HER2-zero, 82 (28.3%) were HER2-low, and 73 (25.2%) were HER2-positive. Modifications in HER2 IHC staining conditions dramatically increased the frequencies of HER2-low BC in cohort 2 (YUH 38.9% and KUDH 49.6%), but they did not result in significant changes in the HER2-positive rates (YUH 15.4% and KUDH 25.2%) compared to cohort 1. In conclusion, minor modifications in HER2 IHC staining conditions significantly affected the frequency of HER2-low BC but had little impact on the HER2-positivity rate. Each pathology laboratory should verify IHC conditions using control slides (including 1+) to enable the accurate identification of HER2-low BC.

Do HER2-Low Tumors Have a Distinct Clinicopathologic Phenotype?

BACKGROUND

Breast cancer subtypes, distinguished by hormone receptor (HR) and HER2 status, have different clinicopathologic features. With recognition of the clinical relevance of HER2-low, there is debate as to whether this is a distinct subtype. Our study aimed to determine whether HER2-low breast cancers have specific clinicopathologic features that differ from those of HER2-negative and HER2-positive cancers.

PATIENTS AND METHODS

A total of 11,072 patients undergoing upfront surgery from 1998 to 2010 were identified from a single-institution prospectively maintained database. HER2 status was classified by immunohistochemistry (IHC)/fluorescence in situ hybridization (FISH) as HER2 negative (41.2%), HER2 low (45%; IHC 1+ or 2+ with negative FISH), and HER2 positive (13.7%), and stratified by HR status. Univariate (UVA) and multivariable multinomial logistic regression analysis (MVA) were performed to determine associations among variables and subtypes.

RESULTS

Compared with HER2-negative tumors, HER2 low was associated with lymphovascular invasion [odds ratio (OR) 1.2, 95% confidence interval (CI) 1.06-1.36; p = 0.003], multifocality (OR 1.26, 95% CI 1.12-1.42; p < 0.001), nodal micrometastasis (OR 1.15, 95% CI 1.02-1.31; p = 0.024), and lower rates of ≥ 3 positive nodes (OR 0.77, 95% CI 0.66-0.90, p = 0.001). When stratified by HR expression, in both HR-positive and HR-negative tumors, age and multifocality were associated with HER2 low on UVA. On MVA, no variables were independently associated with both HR-negative and HR-positive/HER2-low tumors compared with HER2-negative tumors. In contrast, HER2-positive tumors, regardless of HR status, were associated with multifocality and an extensive intraductal component.

CONCLUSION

Clinicopathologic features of HER2-low tumors appear to be primarily related to HR status. Our findings do not support the characterization of HER2 low as a separate subtype.

HER2-low and tumor infiltrating lymphocytes in triple-negative breast cancer: Are they connected?

Most patients with triple-negative breast cancer (TNBC) are not candidates for targeted therapy, leaving chemotherapy as the primary treatment option. Recently, immunotherapy has demonstrated promising results in TNBC, due to its immunogenicity. In addition, a novel antibody-drug conjugate, namely, trastuzumab-deruxtecan, has shown effectiveness in TNBC patients with low-HER2 expression (HER2-low). These novel treatment options raise the question about the potential association between the density of stromal tumor-infiltrating lymphocytes (sTILs) and the level of HER2 expression. We aimed to evaluate the association between the level of HER2 expression (HER2-low versus HER2-0) and density of sTILs in TNBC patients, and how they impact the response to neoadjuvant chemotherapy (NAC). This was a retrospective multicenter study including all TNBC patients diagnosed between 2018 and 2022. Central pathology review included sTILs percentages and level of HER2 expression. Tumors were reclassified as either HER2-0 (HER2 IHC 0) or HER2-low (IHC 1 + or 2 + with negative reflex test). Various clinicopathologic characteristics, including sTILs density, and response to NAC were compared between HER2-0 and HER2-low cases. In total, 753 TNBC patients were included in this study, of which 292 patients received NAC. Interobserver agreement between the original pathology report and central review was moderate (77% had the same IHC status after reclassification in either HER2-0 or HER2-low; k = 0.45). HER2-low TNBC represented about one third (36%) of the tumors. No significant difference in sTILs density or complete pathologic response rate was found between HER2-0 and HER2-low cases (p = 0.476 and p = 0.339, respectively). The density of sTILs (≥ 10% sTILs vs. < 10%) was independently associated with achieving a pCR (p = 0.011). In conclusion, no significant association was found between HER2-low status and density of sTILs nor response to NAC. Nonetheless, sTILs could be an independent biomarker for predicting NAC response in TNBC patients.

New insights into HER2-low breast cancer brain metastasis: A retrospective analysis

BACKGROUND

A considerable number of patients with breast cancer will suffer from brain metastasis in the advanced setting. The HER2 status serves as a significant prognostic factor and the reference of applying treatment for patients with breast cancer brain metastasis (BCBM).

METHODS

Between January 2010 and July 2021, patients with BCBM who had available HER2 status were identified. The patients with HER2 1+ in immunohistochemistry (IHC) or IHC 2+ and fluorescence in situ hybridization (FISH) negative were categorized as HER2-low. Comparisons were conducted between the HER2-low and HER2-zero population. The primary endpoint was overall survival (OS) after the diagnosis of BCBM. Survival outcomes were assessed using Kaplan-Meier curves with log-rank test and Cox proportional hazards model.

RESULTS

In this study, we analyzed 71 patients with the HER2-low breast cancer subtype and 64 patients with the HER2-zero subtype. Despite the limited sample size, our findings revealed a significantly better OS for patients with HER2-low cancer compared to their HER2-zero counterparts (26 m vs 20 m, p = 0.0017). This trend was particularly notable in the HR-negative group (26 m vs 13 m, p = 0.0078), whereas no significant difference was observed among the HR-positive patients. Furthermore, Cox regression analysis revealed that the HER2-low status was an independent prognostic factor for better survival in the HR-negative patients (p = 0.046 in multivariate analysis).

CONCLUSIONS

Patients diagnosed with HER2-low BCBM exhibited a more favorable prognosis than those with HER2-zero BCBM, particularly within the HR-negative subgroup. The low expression of HER2 is supposed to be linked to the prolonged survival of BCBM patients.

High inter-laboratory variability in the assessment of HER2-low breast cancer: a national registry study on 50,714 Danish patients

BACKGROUND

Considering the recent advancements in the treatment of breast cancer with low expression of human epidermal growth factor receptor 2 (HER2), we aimed to examine inter-laboratory variability in the assessment of HER2-low breast cancer across all Danish pathology departments.

METHODS

From the Danish Breast Cancer Group, we obtained data on all women diagnosed with primary invasive breast cancer in 2007-2019 who were subsequently assigned for curatively intended treatment.

RESULTS

Of 50,714 patients, HER2 score and status were recorded for 48,382, among whom 59.2% belonged to the HER2-low group (score 1+ or 2+ without gene amplification), 26.8% had a HER2 score of 0, and 14.0% were HER2 positive. The proportion of HER2-low cases ranged from 46.3 to 71.8% among pathology departments (P < 0.0001) and from 49.3 to 65.6% over the years (P < 0.0001). In comparison, HER2 positivity rates ranged from 11.8 to 17.2% among departments (P < 0.0001) and from 12.6 to 15.7% over the years (P = 0.005). In the eight departments with the highest number of patients, variability in HER2-low cases increased from 2011 to 2019, although the same immunohistochemical assay was used. By multivariable logistic regression, the examining department was significantly related to both HER2 score 0 and HER2 positivity (P < 0.0001) but showed greater dispersion in odds ratios in the former case (range 0.25-1.41 vs. 0.84-1.27).

CONCLUSIONS

Our data showed high inter-laboratory variability in the assessment of HER2-low breast cancer. The findings cast doubt on whether the current test method for HER2 is robust and reliable enough to select HER2-low patients for HER2-targeted treatment in daily clinical practice.

The Significance of Recognition of Human Epidermal Growth Factor 2 Low in Breast Cancer Therapy

In response to recent clinical trials that demonstrate the clinical benefit of antibody-drug conjugate drug therapy in breast cancer (BC) with human epidermal growth factor 2 (HER2) immunohistochemical scores of 1+ or 2+ and negative in situ hybridization results, a new concept of "HER2-low BC" has emerged to describe this newly relevant therapeutic category of BC. Clinical recognition of HER2-low BC has caused a paradigm shift in the therapeutic landscape and management of patients with BC and resulted in rapid changes in clinical practice guidelines. In addition the American Society of Clinical Oncology-College of American Pathologists (ASCO-CAP) recently updated their HER2 Guidelines Recommendations to specifically address HER2-low BC. A literature search in PubMed of peer-reviewed articles, regulatory communications, and relevant practice guidelines pertaining to HER2-low BC was conducted. In this review, we have summarized current published knowledge regarding the clinicopathologic and molecular features, diagnostic criteria, and most current guideline recommendations regarding HER2-low BC, and also highlight ongoing practical and diagnostic challenges when identifying HER2-low BC in routine clinical practice.

Pathologic complete response and survival in HER2-low and HER2-zero early breast cancer treated with neoadjuvant chemotherapy

BACKGROUND

Breast cancers without HER2 amplification but still expressing this membrane protein constitute a new entity called HER2-low tumors. It is important to characterize them in terms of sensitivity to treatment and prognosis.

PATIENTS AND METHODS

To investigate chemosensitivity and long-term prognosis of HER2-low early breast cancer (eBC), compared to HER2-0 tumors, we retrospectively retrieved clinicopathological characteristics, response to treatment, and survival data from 511 patients treated for eBC with neoadjuvant chemotherapy (NAC) in a French cancer center between 2007 and 2018. Factors associated with the achievement of pathologic complete response (pCR) and survival were studied among hormone receptor positive (HR+) and negative (HR-) eBC.

RESULTS

A total of 280 HR+ (61% HER2-low), and 231 HR- (28% HER2-low) eBC were included. We found classical clinicopathological factors usually associated with chemosensitivity and prognosis, in both HR+ and HR- eBC. By uni- and multivariable analysis, HER2 status (low vs 0) was not independently associated with pCR, either in HR+ or HR- eBC. Relapse free (RFS) and overall survival (OS) were not significantly different between HER2-low and HER2-0 among HR+ tumors. In contrast, among HR- negative tumors, RFS and OS were slightly better in HER2-0 eBC by univariable but not by multivariable analysis.

CONCLUSIONS

In eBC patients treated with NAC, taking into account HR expression subtype and other current clinicopathological features, HER2-low tumors did not appear to have different chemosensitivity or prognosis, compared to their HER2-0 counterparts.

HER2-low metastases of HER2-negative primary tumors: a single institution analysis of intertumoral and internodal heterogeneity in node-positive breast cancer

Objective

HER2 status in breast cancer is an essential parameter in individual therapeutic decision-making and is routinely assessed in primary tumors in accordance with international recommendations. Reports of HER2 heterogeneity raise the question of basing treatment decisions on HER2 status in metastases, if present. We investigated the degree and clinical implications of HER2 heterogeneity in lymph node-positive breast cancer. Because of recent recognition of therapeutic opportunities in this group of tumors, we especially focused on cases involving low-level HER2 expression.

Methods

The HER2 status of primary tumors and of corresponding lymph node metastases was determined in archived material at the protein and gene levels using the gene- protein assay and interpreted in accordance with 2018 ASCO/CAP criteria. HER2-low status was defined as protein expression levels 1+ or 2+ with negative amplification status.

Results

We analyzed a series of 43 cases of primary infiltrating breast cancer, each with at least two axillary nodes harboring macrometastases (>2 mm), in total 206 such nodes. In 7% of cases, we detected intertumoral HER2 heterogeneity. Three of nine HER2-positive primary tumors were associated with HER2-negative metastases. No cases with HER2-negative primary tumors had HER2-positive metastases, but 55% (6/11) of HER2 0 primary tumors had HER2 1+ and/or 2+ metastases, and 19% (3/16) HER2 1+ cases had exclusively HER2 0 metastases. All metastases in HER2 2+ cases showed HER2-low protein expression levels. Internodal HER2 heterogeneity at low protein expression levels (presence of HER2 0, HER2 1+, and/or HER2 2+ metastatic deposits within the same axilla) was seen in 40% (17/43) of cases. We found no statistically significant association between HER2 heterogeneity and other tumor-related parameters. Survival data indicated worse outcomes in the HER2-low group compared with the rest of the cohort.

Conclusion

Our results indicate a substantial instability of HER2 protein expression, leading to considerable intertumoral and internodal HER2 heterogeneity in lymph node-positive breast carcinomas. This heterogeneity is particularly relevant in HER2-low tumors in which the corrective effects of HER2 gene copy number analysis definitionally is absent. Our findings suggest that determining HER2 status in metastatic lymph nodes may generate relevant information for therapeutic decision-making.

Incidence, Clinicopathologic Features, HER2 Fluorescence In Situ Hybridization Profile, and Oncotype DX Results of Human Epidermal Growth Factor Receptor 2-Low Breast Cancers: Experience From a Single Academic Center

Human epidermal growth factor receptor 2 (HER2)-low breast cancer, defined by an immunohistochemical (IHC) score of 1+ or 2+ with negative in situ hybridization, is emerging as a predictive marker for the use of the antibody-drug conjugate. To understand how this category differs from HER2-zero cases, we investigated clinicopathological characteristics and HER2 fluorescence in situ hybridization results in a large cohort of 1309 continuous HER2-negative invasive breast carcinomas from 2018 to 2021 evaluated by the Food and Drug Administration-approved HER2 IHC test. Additionally, we compared Oncotype DX recurrence scores and HER2 mRNA expression between HER-low and HER2-zero cases in a separate cohort of 438 estrogen receptor-positive (ER+) early-stage breast carcinoma cases from 2014 to 2016. Based on the cohort from 2018 to 2021, the incidence of HER2-low breast cancers was approximately 54%. HER2-low cases had less frequent grade 3 morphology, less frequent triple-negative results, ER and progesterone receptor negativity, and a higher mean HER2 copy number and HER2/CEP17 ratio than HER2-zero cases (P < .0001). Among ER+ cases, HER2-low cases showed significantly less frequent Nottingham grade 3 tumors. In the cohort from 2014 to 2016, HER2-low cases showed significantly higher ER+ percentages, fewer progesterone receptor-negative cases, lower Oncotype DX recurrence scores, and higher HER2 mRNA expression scores than HER2-zero cases. In summary, this is the first study, to our knowledge, using a large cohort of continuous cases evaluated by the Food and Drug Administration-approved HER2 IHC companion diagnostic test for HER2-low expression and HER2 fluorescence in situ hybridization profile in a real-world setting. Although HER2-low cases showed a higher HER2 copy number, ratio, and mRNA level than HER2-zero cases statistically, such small differences are unlikely to be biologically or clinically meaningful. However, our study suggests that HER2-low/ER+ early-stage breast carcinoma may represent a less aggressive group of breast carcinoma, given its association with a lower Nottingham grade and Oncotype DX recurrence score.

The effect of low HER2 expression on treatment outcomes in metastatic hormone receptor positive breast cancer patients treated with a combination of a CDK4/6 inhibitor and endocrine therapy: A multicentric retrospective study

BACKGROUND

CDK4/6 inhibitors combined with endocrine therapy have significantly improved treatment outcomes for metastatic hormone receptor-positive (HR+) breast cancer patients. However, the impact of low HER2 expression on treatment response and progression-free survival (PFS) remains unclear.

METHODS

This multicenter retrospective study included 204 HR+ breast cancer patients treated with a combination of CDK4/6 inhibitor and endocrine therapy. HER2-zero disease was detected in 138 (68%) and HER2-low disease in 66 (32%) patients. Treatment-related characteristics and clinical outcomes were analyzed, with a median follow-up of 22 months.

RESULTS

The objective response rate (ORR) was 72.7% in the HER2 low group and 66.6% in the HER2 zero group (p = 0.54). Median PFS was not significantly different between the HER2-low and HER2 zero groups (19 months vs.18 months, p = 0.89), although there was a trend toward longer PFS in the HER2-low group for first-line treatment (24 months progression-free survival rate 63% vs 49%). In recurrent disease, the median PFS was 25 months in the HER2-low group and 12 months in the HER2-zero group (p = 0.08), while in de novo metastatic disease, the median PFS was 18 months in the HER2-low group and 27 months in the HER2-zero group (p = 0.16). The order of CDK4/6 inhibitor use and the presence of visceral metastasis were identified as independent variables affecting PFS.

CONCLUSION

Low HER2 expression did not significantly impact treatment response or PFS in HR+ breast cancer patients treated with a CDK4/6 inhibitor and endocrine therapy. Because of the conflicting results in the literature, further prospective studies are needed to evaluate the clinical significance of HER2 expression in HR+ breast cancer.