Survival outcomes in HER2-low versus HER2-zero breast cancer after neoadjuvant chemotherapy: a meta-analysis

BACKGROUND

The survival outcomes in HER2-low versus HER2-zero breast cancer (BC) after neoadjuvant chemotherapy (NACT) remain unclear. The meta-analysis was conducted to summarize current evidence about the survival outcomes in HER2-low versus HER2-zero BC.

METHODS

We conducted a systematic search in PubMed and EMBASE databases to identify relevant studies.

RESULTS

A total of 14 studies with 53,714 patients were included. Overall, 34,037 patients (63.37%) were HER2-low, and 19,677 patients (36.63%) were HER2-zero. Patients with HER2-low tumors had a significantly lower pathological complete response (pCR) rate than patients with HER2-zero tumors, regardless of the hormone receptor status. Compared with HER2-zero breast cancer, the overall survival (OS) and disease-free survival (DFS) of HER2-low BC were longer in the overall cohort (HR = 0.72; 95% CI = 0.61-0.85; P < 0.0001; HR = 0.83; 95% CI = 0.75-0.92; P = 0.0002); however, no differences were observed in terms of OS and DFS between HER2-low and HER2-zero BC in the HR-negative group. In the HR-positive group, HER2-low status had no significant impact on OS, while significantly associated with increased DFS (HR = 0.85; 95% CI = 0.76-0.96; P = 0.007).

CONCLUSION

These results suggest that although HER2-low BC has a poor response to NACT, it is correlated with favorable OS and DFS after NACT in the overall cohort as well as longer DFS in the HR-positive group.

The association between HER2-low status and survival in patients with metastatic breast cancer treated with Cyclin-dependent kinases 4 and 6 inhibitors: a systematic review and meta-analysis

PURPOSE

The cyclin-dependent kinase (CDK) 4/6 inhibitors significantly altered the treatment landscape of hormone-positive (HR+), HER2- metastatic breast cancer (MBC). However, biomarkers predicting long-term benefit and early progression are yet to be defined. Several studies suggested the possibility of diminished efficacy in patients with HER2-low disease. Therefore, we conducted a systematic review and meta-analysis to evaluate the association between low-level HER2 expression and efficacy outcomes (PFS, OS, ORR) with CDK 4/6 inhibitors.

METHODS

The Pubmed, Web of Science, and Scopus databases were used to systematically filter the published studies from inception to 08 August 2023 for this systemic review. Studies including MBC patients treated with CDK 4/6 inhibitors and reported survival outcomes according to HER2 expression were included. We performed the meta-analyses with the generic inverse-variance method with a fixed-effects model and used HRs with 95% two-sided CIs as the principal summary measure.

RESULTS

Nine studies encompassing 2705 patients were included in the analyses. In the pooled analysis of nine studies, the risk of progression and/or death was higher in patients with HER2-low tumors compared to HER2-zero (HR: 1.22, 95% CI 1.10-1.35, p < 0.001). In the pooled analysis of five studies, although the median follow-up was short, the risk of death was higher in the HER2-low group compared to the HER2-zero group (HR: 1.22, 95% CI 1.04-1.44, p = 0.010).

CONCLUSION

The available evidence demonstrates a significantly higher risk of progression or death with CDK 4/6 inhibitors in HER2-low tumors. Further research is needed to improve outcomes in patients with HR+-HER2-low tumors.

The Modified Neo-Bioscore System for Staging Breast Cancer Treated with Neoadjuvant Therapy Based on Prognostic Significance of HER2-Low Expression

Background: Recently, the classification of HER2 status evolves from binary to ternary, and HER2-low expression may exhibit prognostic significance. We aimed to investigate whether HER2-low tumor is distinct from HER2-zero or HER2-positive tumors, and then to develop a modified staging system (mNeo-Bioscore) that incorporates HER2-low status into Neo-Bioscore. Patients and Methods: This cohort study was conducted using data from the prospective database on breast cancer patients between January 2014 and February 2019. Results: Among 259 patients enrolled in the study, the HER2-low tumor exhibited significantly lower histological grade, pathological staging and Ki-67 level than the other two groups. HER2-low patients and HER2-positive patients receiving concurrent HER2-directed therapy may have similar LRFS (p = 0.531) and OS (p = 0.853), while HER2-zero peers may have significantly worse LRFS (p = 0.006) and OS (p = 0.017). In particular, a similar trend was also found in the patients without pathological complete response after surgery. Incorporation of HER2-low status made improvement in fit: 5-year OS rate estimates ranged from 33.33% to 100% for mNeo-Bioscore vs 61.36% to 100% for Neo-Bioscore. Conclusions: This study demonstrated that HER2-low tumor may exhibit prognostic significance. The innovative mNeo-Bioscore, based on a new classification of HER2 status, may serve as a prognostic staging system superior to Neo-Bioscore.

Prognostic value and relapse pattern of HER2-low in hormone receptor-positive breast cancer

BACKGROUND

A new concept of HER2-low has emerged in recent years. However, the prognostic value and the relapse pattern of HER2-low is unclear.

METHODS

Our study included patients diagnosed with HER2-negative/hormone receptor-positive breast cancer to explore the differences in survival outcomes between the HER2-low group and the HER2-zero group. More importantly, we explored different recurrence patterns, including the comparison of metastatic sites and recurrence time curve between the two groups.

RESULTS

A total of 797 patients with hormone receptor-positive breast cancer were analyzed. Similar disease-free survival (DFS) was observed between the HER2-low group and HER2-zero group (HR 0.84, 95% CI: 0.61-1.16, p = 0.290). There was also no significant difference in OS between the HER2-low group and the HER2-zero group (HR 0.77, 95% CI: 0.46-1.28, p = 0.310). When IHC 1+ and 0 were taken as a group, the IHC 2+ group had significantly better DFS than the IHC 1+ and 0 group in some subgroups. The risk of bone metastasis in patients with HER2 IHC 1+ and 0 was significantly higher than that of patients with HER2 IHC 2+ (12.7% vs. 4.7%, p < 0.001). Compared with the HER2-zero group, we found that the HER2-low group had a more obvious peak in mortality at the time of postoperative 80th-100th month.

CONCLUSIONS

No significant difference in DFS and OS between the HER2-low group and the HER2-zero group was observed. Patients with HER2 IHC 1+ and 0 tend to develop bone metastasis. The HER2-low group had a more obvious second peak in mortality.

Unveiling the HER2-low phenomenon: exploring immunohistochemistry and gene expression to characterise HR-positive HER2-negative early breast cancer

PURPOSE

HER2-low breast cancer (BC) is a novel entity with relevant therapeutic implications, especially in hormone receptor (HR) positive BC. This study examines whether HER2 mRNA through the 21-gene assay, Oncotype DX (ODX), can refine the diagnosis of HER2-low and HER2-zero, obtained by immunohistochemistry (IHC).

METHODS

Between Jan 2021 and Jan 2023, 229 consecutive HR-positive HER2-negative early BC (T1-3 N0-1) have been characterised by IHC and ODX. HER2 status by IHC was either zero (IHC-0) or low (IHC-1 + and IHC-2 + /ISH-negative) while HER2-zero was further divided into HER2-null (IHC-0) and HER2-ultralow (IHC-1-10%). HER2 gene expression by ODX was negative if lower 10.7.

RESULTS

The distribution of HER2 IHC was as follows: 53.3% HER2-0, 29.25% HER2-1 + , and 17.5% HER2-2 + . The clinicopathological characteristics were similar in the three groups, with higher PgR-negative rate in HER2-zero (13.9% vs 3% vs 5%). The distribution of RS was homogeneous in the three groups with the median HER2 gene expression of 9.20 [IQR: 8.70-9.60]. HER2 gene expression gradually increased as the IHC score, with substantial overlap. After adjusting for confounders, HER2-1 + and HER2 2 + had a significant positive correlation between HER2 gene expression and IHC [OR 1.42, 95% CI 1.21 to 1.68, p < 0.001; OR 1.96, 95% CI 1.61 to 2.37, p < 0.001] compared to the HER2-zero group. HER2 gene expression did not differ between HER2-null and HER2-ultralow subgroups.

CONCLUSION

Due to the substantial overlap, the HER2 gene expression is unable to properly distinguish HER2-low and HER2-zero IHC whose accurate identification is critical in the context of HER2-negative BC.

Impact of HER2-low status for patients with early-stage breast cancer and non-pCR after neoadjuvant chemotherapy: a National Cancer Database Analysis

PURPOSE

To investigate potential differences in pathological complete response (pCR) rates and overall survival (OS) between HER2-low and HER2-zero patients with early-stage hormone receptor (HR)-positive and triple-negative breast cancer (TNBC), in the neoadjuvant chemotherapy setting.

METHODS

We identified early-stage invasive HER2-negative BC patients who received neoadjuvant chemotherapy diagnosed between 2010 and 2018 in the National Cancer Database. HER2-low was defined by immunohistochemistry (IHC) 1+ or 2+ with negative in situ hybridization, and HER2-zero by IHC0. All the methods were applied separately in the HR-positive and TNBC cohorts. Logistic regression was used to estimate the association of HER2 status with pCR (i.e. ypT0/Tis and ypN0). Kaplan-Meier method and Cox proportional hazards model were applied to estimate the association of HER2 status with OS. Inverse probability weighting and/or multivariable regression were applied to all analyses.

RESULTS

For HR-positive patients, 70.9% (n = 17,934) were HER2-low, whereas 51.1% (n = 10,238) of TNBC patients were HER2-low. For both HR-positive and TNBC cohorts, HER2-low status was significantly associated with lower pCR rates [HR-positive: 5.0% vs. 6.7%; weighted odds ratio (OR) = 0.81 (95% CI: 0.72-0.91), p < 0.001; TNBC: 21.6% vs. 24.4%; weighted OR = 0.91 (95% CI: 0.85-0.98), p = 0.007] and improved OS [HR-positive: weighted hazard ratio = 0.85 (95% CI: 0.79-0.91), p < 0.001; TNBC: weighted hazard ratio = 0.91 (95% CI: 0.86-0.96), p < 0.001]. HER2-low status was associated with favorable OS among patients not achieving pCR [HR-positive: adjusted hazard ratio = 0.83 (95% CI: 0.77-0.89), p < 0.001; TNBC: adjusted hazard ratio = 0.88 (95% CI 0.83-0.94), p < 0.001], while no significant difference in OS was observed in patients who achieved pCR [HR-positive: adjusted hazard ratio = 1.00 (95% CI: 0.61-1.63), p > 0.99; TNBC: adjusted hazard ratio = 1.11 (95% CI: 0.85-1.45), p = 0.44].

CONCLUSION

In both early-stage HR-positive and TNBC patients, HER2-low status was associated with lower pCR rates. HER2-zero status might be considered an adverse prognostic factor for OS in patients not achieving pCR.

Prognostic value of HER2-low status in breast cancer: a systematic review and meta-analysis

BACKGROUND

Human epidermal growth factor receptor 2 (HER2)-low expression in breast cancer has been recently identified as a new therapeutic target. However, it is unclear if HER2-low status has an independent impact on prognosis.

MATERIALS AND METHODS

A systematic literature research was carried out to identify studies comparing survival outcomes of patients affected by HER2-low versus HER2-zero breast cancer. Using random-effects models, pooled hazard ratios (HRs) and odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for progression-free survival (PFS) and overall survival (OS) in the metastatic setting as well as disease-free survival (DFS), OS and pathological complete response (pCR) in the early setting. Subgroup analyses by hormone receptor (HoR) status were carried out. The study protocol is registered on PROSPERO (n.CRD42023390777).

RESULTS

Among 1916 identified records, 42 studies including 1 797 175 patients were eligible. In the early setting, HER2-low status was associated with significant improved DFS (HR 0.86, 95% CI 0.79-0.92, P < 0.001) and OS (HR 0.90, 95% CI 0.85-0.95, P < 0.001) when compared to HER2-zero status. Improved OS was observed for both HoR-positive and HoR-negative HER2-low populations, while DFS improvement was observed only in the HoR-positive subgroup. HER2-low status was significantly associated with a lower rate of pCR as compared to HER2-zero status both in the overall population (OR 0.74, 95% CI 0.62-0.88, P = 0.001) and in the HoR-positive subgroup (OR 0.77, 95% CI 0.65-0.90, P = 0.001). In the metastatic setting, patients with HER2-low breast cancers showed better OS when compared with those with HER2-zero tumours in the overall population (HR 0.94, 95% CI 0.89-0.98, P = 0.008), regardless of HoR status. No significant PFS differences were found.

CONCLUSIONS

Compared with HER2-zero status, HER2-low status appears to be associated with a slightly increased OS both in the advanced and early settings, regardless of HoR expression. In the early setting, HER2-low tumours seem to be associated to lower pCR rates, especially if HoR-positive.

Differences in Treatment Outcomes Between Patients with HER2-Low versus HER2-Zero, Hormone Receptor-Positive Advanced-Stage Breast Cancer Treated with Ribociclib

Background

Metastatic breast cancers (MBC) with no expression of human epidermal growth factor receptor-2 (HER2) are recently classified into two groups; HER2-zero [HER2-immunohistochemistry (IHC) score of 0 (IHC-0)] and HER2-low, defined as those with IHC score of 1+ or 2+ with negative in situ hybridization (ISH) assay. We investigate differences in treatment outcomes between both groups treated with endocrine therapy (ET) and the CDK4/6 inhibitor ribociclib.

Methods

Data were retrospectively collected for patients with HR-positive+/HER2-negative MBC who received ribociclib with an aromatase inhibitor (AI) or fulvestrant and were divided into two groups: HER2-zero and HER2-low.

Results

A total of 257 patients, median age 48 (22-87) years, all with MBC who were treated with ET and ribociclib were enrolled. One hundred and thirty-seven (53.3%) patients had de novo MBC, and majority (n = 162, 63.0%) received ribociclib as a first-line therapy. In total, 114 (44.4%) patients had HER2-zero (IHC-0), while 143 (55.6%) others had HER2-low disease. The overall response rate (ORR) was 52.0% for the HER2-zero group compared to 39.4% for the HER2-low group, p = 0.005. The median PFS was 22.2 (95% confidence interval [CI], 19.4-NR) months for HER2-zero versus 17.3 (95% CI, 14.1-20.6) months for HER2-low, P = 0.0039. In multivariable analysis, HER2-low expression remained significant determinant of inferior PFS after adjusting for other factors, including the site of metastasis, prior chemotherapy, and the line of treatment.

Conclusion

In patients with MBC treated with ET and ribociclib, level of HER2 negativity may affect treatment outcomes; patients with HER2-zero had better response rate and PFS compared to those with HER2-low disease. These findings, if confirmed in larger studies, may help oncologists select patients with HER2-low for better treatment options.

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.

Comparison of HER2-zero and HER2-low in terms of clinicopathological factors and survival in early-stage breast cancer: A systematic review and meta-analysis

BACKGROUND

The prognostic differences between HER2-zero and HER2-low breast cancer (BC) remain unclear. Purpose of this meta-analysis is to investigate the differences between HER2-low and HER2-zero in terms of clinicopathological factors and survival outcomes in early-stage BC.

METHODS

We searched major databases and congress proceedings until November 1, 2022 to identify studies comparing HER2-zero and HER2-low in early-stage BC. HER2-zero immunohistochemically (IHC) was defined as score 0, while HER2-low was defined as IHC 1+ or 2+/in situ hybridization negative.

RESULT

A total of 23 retrospective studies involving 636,535 patients were included. HER2-low rate was 67.5% in the hormone receptor (HR)-positive group, while this rate was 48.6% in the HR-negative group. In the analysis of clinicopathological factors by HR status, the proportion of premenopausal patients within the HR-positive group was greater in the HER2-zero arm (66.5% vs 61.8%), whereas grade 3 tumors (74.2% vs 71.5%), patients younger than 50 years of age (47.3% vs 39.6%), and T3-T4 tumors (7.7% vs 6.3%) within the HR-negative group was higher in the HER2-zero arm. In both the HR-positive and HR-negative groups, the HER2-low arm showed significantly improved results for disease-free survival (DFS) and overall survival (OS). The hazard ratios for DFS and OS in the HR-positive group were 0.88 (95% CI 0.83-0.94) and 0.87 (95% CI 0.78-0.96), respectively. In the HR-negative group, the hazard ratios for DFS and OS were 0.87 (95% CI 0.79-0.97) and 0.86 (95% CI 0.84-0.89), respectively.

CONCLUSION

In early-stage BC, HER2-low is associated with better DFS and OS compared to HER2-zero, regardless of HR status.

Discordance of HER2-Low between Primary Tumors and Matched Distant Metastases in Breast Cancer

We examined differences in HER2 expression between primary tumors and distant metastases, particularly within the HER2-negative primary breast cancer cohort (HER2-low and HER2-zero). The retrospective study included 191 consecutive paired samples of primary breast cancer and distant metastases diagnosed between 1995 and 2019. HER2-negative samples were divided into HER2-zero (immunohistochemistry [IHC] score 0) and HER2-low (IHC score 1+ or 2+/in situ hybridization [ISH]-negative). The main objective was to analyze the discordance rate between matched primary and metastatic samples, focusing on the site of distant metastasis, molecular subtype, and de novo metastatic breast cancer. The relationship was determined by cross-tabulation and calculation of Cohen's Kappa coefficient. The final study cohort included 148 paired samples. The largest proportion in the HER2-negative cohort was HER2-low [primary tumor 61.4% (n = 78), metastatic samples 73.5% (n = 86)]. The discordance rate between the HER2 status of primary tumors and corresponding distant metastases was 49.6% (n = 63) (Kappa -0.003, 95%CI -0.15-0.15). Development of a HER2-low phenotype occurred most frequently (n = 52, 40.9%), mostly with a switch from HER2-zero to HER2-low (n = 34, 26.8%). Relevant HER2 discordance rates were observed between different metastatic sites and molecular subtypes. Primary metastatic breast cancer had a significantly lower HER2 discordance rate than secondary metastatic breast cancer [30.2% (Kappa 0.48, 95%CI 0.27-0.69) versus 50.5% (Kappa 0.14, 95% CI -0.03-0.32)]. This highlights the importance of evaluating potentially therapy-relevant discordance rates between a primary tumor and corresponding distant metastases.

Clinicopathologic characteristics and prognostic significance of HER2-low expression in patients with early breast cancer: A systematic review and meta-analysis

Background

HER2-low expression breast cancer (BC) accounts for approximately 45%-55% of all BC cases. The purpose of this study was to investigate the prognostic difference between patients with HER2-low expression and HER2-zero BC.

Methods

An electronic search of Pubmed, Embase, Cochrane Library, and Web of Science databases was performed to screen studies that included prognostic comparisons between HER2-zero and HER2-low expression groups. A total of 14 studies involving 52106 patients were included.

Results

Our results indicated that HER2-low expression was associated with a significant benefit in OS among all patients with early BC (HR, 0.83; 95% CI, 0.78-0.88), patients with hormone-receptor positive BC (HR, 0.83; 95% CI, 0.77-0.89), and patients with TNBC (HR, 0.78; 95% CI, 0.70-0.87). HER2-low expression was associated with a significant benefit in DFS among all patients (HR, 0.81; 95% CI, 0.71-0.93), patients with hormone receptor-positive BC (HR, 0.81; 95% CI, 0.72-0.90), but no significant difference in DFS was found in patients with TNBC (HR, 0.87; 95% CI, 0.65-1.17). HER2-low expression was associated with a significant benefit in RFS among all patients (HR, 0.90; 95% CI, 0.85-0.95), patients with hormone receptor-positive BC (HR, 0.90; 95% CI, 0.84-0.96), but no significant difference in RFS was found in patients with TNBC (HR, 0.80; 95% CI, 0.55-1.16).

Conclusions

Among patients with early-stage BC, patients with HER2-low expression BC had better OS in the overall population, hormone receptor-positive and TNBC subgroups. Besides, favorable DFS and RFS were observed in both the overall population and hormone receptor-positive subgroup.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier (CRD 42022349458).

Pathological complete response, long-term outcomes, and recurrence patterns in HER2-low versus HER2-zero breast cancer after neoadjuvant chemotherapy

BACKGROUND

The interest in HER2-low breast cancer (BC) has increased in recent years with the development of novel anti-HER2 antibody-drug conjugates. Here, we investigated the clinical outcomes and relapse patterns of patients with HER2-low or -zero BCs in an Asian population.

METHODS

We retrospectively identified HER2-low or -zero BC patients with stage I-III tumours who were treated with neoadjuvant chemotherapy and underwent curative surgery, between 2014 and 2018 at Asan Medical Center, Seoul, Korea.

RESULTS

A total of 818 and 754 HER2-zero and HER2-low BC patients, respectively, were consecutively included in this analysis. The HER2-low group had more hormone receptor [HR]-positive patients (81% versus 56%, P < 0.001). The HER2-zero group had a higher proportion of patients who achieved pathological complete response (pCR) (14.7% versus 9.8%, P = 0.003); however, no significant differences of pCR rate by HER2 status were identified in the HR-positive (P = 0.4) and HR-negative groups (P = 0.3) when analysed separately. The HER2-low BC cases had higher 5-year overall survival (OS) and disease-free survival (DFS) rates (P < 0.001 for OS; P = 0.002 for DFS); however, no differences were observed in terms of OS and DFS by HER2 status in the HR-positive group (P = 0.21 for OS and P = 0.66 for DFS).

CONCLUSIONS

Our current findings do not support that HER2-low BC had different biology and clinical features compared to HER2-zero BC in patients who treated with neoadjuvant chemotherapy. However, the prognostic impact of HER2-low status in BC remains controversial; thus warranting further research.

Long-term prognostic significance of HER2-low and HER2-zero in node-negative breast cancer

BACKGROUND

Recently, novel antibody--drug conjugates (ADCs) showed clinical activity in a subset of advanced human epidermal growth factor receptor 2 (HER2)-negative patients. We investigated the prognostic significance of HER2-low and HER2-zero tumours.

PATIENTS AND METHODS

The retrospective cohort study included 410 consecutive node-negative breast cancer patients without adjuvant systemic therapy treated between 1985 and 2000 (median follow-up: 16.73 [IQR 8.58-23.45] years). 351 (85.6%) were HER-2 negative and subdivided into HER2-zero (immunohistochemistry [IHC] score 0) and HER2-low (IHC score 1+ or 2+/in situ hybridisation [ISH]-negative). HER2 gene expression was available in 170 (48.4%) patients. Differences in HER2 status for immunohistochemistry, gene expression and clinico-pathologic parameters were assessed using Fisher's exact test, Pearson's correlation and Mann-Whitney test. Prognosis was investigated using the Kaplan-Meier method and Cox regression analyses.

RESULTS

Of the 351 HER2-negative patients, 198 (56.4%) had HER2-low tumours and 153 (43.6%) were HER2-zero. Significant differences between HER2-zero and HER2-low tumours were found in histologic grading (P = 0.001), Ki-67 (P = 0.013) and HER2 gene expression (P = 0.002). HER2-low patients had significantly longer disease-free survival (DFS) (15-year rate: 67.5% [95% CI 61.0-74.7] vs. 47.3% [95% CI 39.9-56.1], P < 0.001) and overall survival (OS) (15-year rate: 75.4% [95% CI 69.4-81.9] vs. 66.8% [95% CI 59.5-74.9], P = 0.009). The OS difference was observed in hormone receptor (HR)-positive (P = 0.039) but not HR-negative (P = 0.086) tumours. The results of multivariable analyses confirmed the independent prognostic significance of HER2 status (DFS: HR, 0.546; 95% CI, 0.402-0.743; P < 0.001; OS: HR, 0.653; 95% CI, 0.458-0.932; P = 0.019).

CONCLUSION

HER2-low patients had a better survival than HER2-zero patients.