Impact of Human Epidermal Growth Factor Receptor 2 (HER2) Low Status in Response to Neoadjuvant Chemotherapy in Early Breast Cancer

HER2-Low Breast Cancer: Now and in the Future

Breast cancer is a heterogeneous disease, and its subtypes are characterized by hormone receptor and human epidermal growth factor receptor 2 (HER2) expression status. "HER2-low" tumors, which exhibit a low level of HER2 expression (immunohistochemistry 1+ or 2+ without gene amplification), were conventionally considered not amenable to anti-HER2 targeting agents based on the results of a phase III trial of trastuzumab. However, this perspective is being challenged by the emergence of novel anti-HER2 antibody-drug conjugates, such as trastuzumab-deruxtecan. These innovative therapies have demonstrated remarkable efficacy against HER2-low breast cancer, shedding new light on a previously overlooked category of breast cancer. Such promising results highlight the need for in-depth investigations of the biology and prognostic implications of HER2-low tumors. In this review, we comprehensively summarize the current evidence surrounding this topic and highlight areas that warrant further exploration and research in the future.

Insights Into the Emerging Entity of HER2-Low Breast Cancer

Human epidermal growth factor receptor 2 (HER2)-low breast cancer (BC) is a subtype of BC that has been recently recognized as a separate clinical entity with distinct clinical and molecular characteristics. It is defined by a low level of HER2 protein expression, which distinguishes it from other more aggressive BC subtypes. Early studies suggest that it may have a more favorable prognosis than HER2-positive BC, as it is less likely to spread to other parts of the body and may be more responsive to standard BC treatments such as chemotherapy, radiation therapy, and hormone therapy. Given the relative new emergence of HER2-low BC, there is still much to be learned about this subtype; ongoing research is focused on identifying the underlying genetic mutations that contribute to HER2-low BC as well as developing targeted therapies that can improve outcomes for patients with this disease. This review is aimed at summarizing the current clinical knowledge on HER2-low BC, with the aim of creating a better understanding of this entity and paving the way for potential interventions and a new standard of care.

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.

Effect of HER2-low expression on neoadjuvant efficacy in operable breast cancer

OBJECTIVE

To investigate the effects of HER2-low expression (HER2-low) and HER2-zero expression (HER2-0) on the pathological complete response (pCR) rate and survival of patients following neoadjuvant chemotherapy.

METHODS

Eighty-six patients were followed up. Patients were divided into HER2-0 (immunohistochemistry (IHC) score of 0 (IHC0)) and HER2-low (IHC1+ or IHC2+/in situ hybridization non-amplified (ISH-)) groups according to the IHC detection of puncture tissues. After neoadjuvant chemotherapy, the clinical characteristics, pCR rate and DFS were compared between the two groups.

RESULTS

There were 24 (27.9%) cases with HER2-0 and 62 (72.1%) cases with HER2-low. Hormone receptor-positive (HR+) patients accounted for 77.4% of the HER2-low group, which was higher than 70.8% in the HER2-0 group, and there was no significant difference between the two groups (p = 0.524). There were statistical differences in the pT and pN stages between HER2-low and HER2-0 subgroups in the triple-negative breast cancer (TNBC) group after neoadjuvant chemotherapy. The HER2-low subgroup had an earlier T stage (p = 0.009), and the ratio of N0 to N1 in the HER2-low and HER2-0 subgroups was 92.9% and 71.4%, respectively (p = 0.037). The Ki-67 index and median PR value were significantly lower in the HER2-low group after neoadjuvant chemotherapy (p = 0.002, p = 0.018). The HER2 IHC score was altered in the HER2-low group, and the HER-2 (2+) score changed significantly (p = 0.002). Seventy-eight patients with complete immunohistochemical data were analyzed. The discordance rate of the IHC score of HER2 after neoadjuvant chemotherapy was 38.5%, and eight patients with HER2-low showed HER2-0 status, with a discordance rate of 10.3%. After neoadjuvant chemotherapy, The pCR rate was significantly lower in the HER2-low group compared with that in the HER2-0 group (4.8% vs. 8.3%; p = 0.914), but the recurrence and metastasis rates were lower in the HER2-low group (9.7% vs. 20.8%; p = 0.165). There were no differences in DFS between the two groups at 6, 12, 24, and 36 months (p = 0.076; p = 0.518; p = 0.245; p = 0.406). The subgroup analysis demonstrated no significant difference in DFS between HER2-low and HER2-0 subgroups in the HR + and TNBC groups (p = 0.141, p = 0.637).

CONCLUSION

This retrospective study indicates that HER2-low has no significant effect on neoadjuvant efficacy in operable breast cancer. There were no statistical differences in clinical characteristics, pCR rate, and DFS between the HER2-low and the HER2-0 groups. There was no evidence that a HER2-low status constitutes a unique biological subtype, suggesting that more clinical data might be needed to verify these observations.

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.

Effect of HER2-low-positive status on neoadjuvant chemotherapy and survival outcome of breast cancer: a 10-year dual-center retrospective study

Various novel HER2-targeted antibody-conjugated drugs (ADCs) have shown satisfactory antitumor activity in HER2-low-positive breast cancer (BC). It is urgent to clarify whether HER2-low-positive tumors have unique biological behavior and should be considered a new molecular subtype. We screened eligible BC patients and collected relevant information at the First Hospital of Jilin University and the First Affiliated Hospital of Xi'an Jiaotong University from January 2010 to December 2020. A total of 1027 patients were included in our study cohort, and 66.0% (678/1027) had HER2-low-positive tumors. Compared to HER2-zero patients, HER2-low-positive patients tended to have more lymph node metastasis, a larger proportion of hormone receptor (HR)-positive tumors, and a lower proliferation rate (Ki-67). The pathologic complete response (pCR) rate of HER2-low-positive patients was lower than that of HER2-zero patients (19.3% vs 26.1%), especially in the HR-positive subgroup (12.00% vs 20.29%). However, multivariate logistic regression analysis showed that HER2 status was not an independent factor for predicting pCR. HER2-low-positive patients had a higher overall survival (OS) rate in the HR-positive subgroup. The Cox regression model analysis suggested that HER2-low-positive status did not statistically significantly affect the survival outcomes, regardless of disease-free survival (DFS) (P=0.308) or OS (P=0.066). In conclusion, HER2-low-positive tumors have unique clinical and pathological characteristics, with a lower pCR rate in the HR-positive subgroup and better survival in the HR-negative subgroup compared to HER2-zero tumors. However, the effect of HER2-low-positive status on pCR or survival outcomes was not statistically significant.

Low and Ultra-Low HER2 in Human Breast Cancer: An Effort to Define New Neoplastic Subtypes

HER2-low and ultra-low breast cancer (BC) have been recently proposed as new subcategories of HER2 BC, supporting a re-consideration of immunohistochemical negative scores of 0, 1+ and the 2+/in situ hybridization (ISH) negative phenotype. In the present review, we outline the criteria needed to exactly distinguish HER2-low and ultra-low BC. Recent clinical trials have demonstrated significant clinical benefits of novel HER2 directing antibody-drug conjugates (ADCs) in treating these groups of tumors. In particular, trastuzumab-deruxtecan (T-Dxd), a HER2-directing ADC, has been recently approved by the US Food and Drug Administration as the first targeted therapy to treat HER2-low BC. Furthermore, ongoing trials, such as the DESTINY-Breast06 trial, are currently evaluating ADCs in patients with HER2-ultra low BC. Finally, we hope that new guidelines may help to codify HER2-low and ultra-low BC, increasing our knowledge of tumor biology and improving a targetable new therapeutical treatment.

Comparison of the pCR Rate and DFS Among Breast Cancer Patients with Different Hormone Receptor and HER2 Statuses

Background

Recent studies have investigated the features of breast cancer (BC) with low human epidermal growth factor receptor 2 (HER2) expression or HER2-0 expression. However, the results were inconsistent. In this study, we investigated the differences in the pathological complete response (pCR) rate and disease-free survival (DFS) between HER2-low and HER2-0 BC patients and between subgroups.

Methods

HER2-negative BC patients who received neoadjuvant chemotherapy between January 2013 and December 2019 in our hospital were retrospectively reviewed. First, the pCR rate and DFS were compared between HER2-low and HER2-0 patients and among different hormone receptor (HR) and HER2 statuses. Subsequently, DFS was compared between different HER2 status populations with or without pCR. Finally, a Cox regression model was used to identify the prognostic factors.

Results

Overall, 693 patients were selected: 561 were HER2-low, and 132 were HER2-0. Between the two groups, there were significant differences in N stage (P = 0.008) and HR status (P = 0.007). No significant difference in the pCR rate (12.12% vs 14.39%, P = 0.468) or DFS was observed, independent of HR status. HR+/HER2-low patients had a significantly worse pCR rate (P < 0.001) and longer DFS (P < 0.001) than HR-/HER2-low or HER2-0 patients. In addition, a longer DFS was found in HER2-low patients versus HER2-0 patients among those who did not achieve pCR. Cox regression showed that N stage and HR status were prognostic factors in the overall and HER2-low populations, while no prognostic factor was found in the HER2-0 group.

Conclusion

This study suggested that HER2 status is not associated with the pCR rate or DFS. Longer DFS was found only among patients who did not achieve pCR in the HER2-low versus HER2-0 population. We speculated that the interaction of HR and HER2 might have played a crucial role in this process.

Prognostic effect of HER2 evolution from primary breast cancer to breast cancer metastases

Purpose

Therapeutic options for breast cancer (BC) treatment are constantly evolving. The Human Epidermal Growth Factor 2 (HER2)-low BC entity is a new subgroup, representing about 55% of all BC patients. New antibody–drug conjugates demonstrated promising results for this BC subgroup. Currently, there is limited information about the conversion of HER2 subtypes between primary tumor and recurrent disease.

Methods

This retrospective study included women with BC at the University Medical Centre Wuerzburg from 1998 to 2021. Data were retrieved from patients' records. HER2 evolution from primary diagnosis to the first relapse and the development of secondary metastases was investigated.

Results

In the HR-positive subgroup without HER2 overexpression, HER2-low expression in primary BC was 56.7 vs. 14.6% in the triple-negative subgroup (p < 0.000). In the cohort of the first relapse, HER2-low represented 64.1% of HR-positive vs. 48.2% of the triple-negative cohort (p = 0.03). In patients with secondary metastases, HER2-low was 75.6% vs. 50% in the triple negative subgroup (p = 0.10). The subgroup of HER2-positive breast cancer patients numerically increased in the course of disease; the HER2-negative overall cohort decreased. A loss of HER2 expression from primary BC to the first relapse correlated with a better OS (p = 0.018). No clinicopathological or therapeutic features could be identified as potential risk factors for HER2 conversion.

Conclusion

HER2 expression is rising during the progression of BC disease. In view of upcoming therapeutical options, the re-analysis of newly developed metastasis will become increasingly important.

Moving HER2-low breast cancer predictive and prognostic data from clinical trials into the real world

Background: Previous data, mostly from clinical trials, reported that HER2-low status is associated with low pathological complete response (pCR), and favourable prognosis. Since these findings suggest the existence of an additional breast cancer subtype, we questioned if the predictive/prognostic value of HER2-low was also relevant in the real world.

Methods: Data from non-metastatic breast cancer patients treated with neoadjuvant chemotherapy and surgery (2009–2020) were retrieved from our institutional prospectively-maintained registry. Univariable and multivariable logistic models were implemented to study the association between pCR and baseline HER2 status. Univariable analysis of disease-free survival (DFS) was performed through Kaplan-Meier survival curves and log-rank tests.

Results: Starting from a total of 790 consecutive cases, we identified 444 newly-diagnosed breast cancer patients featuring HER2 immunohistochemistry (IHC) 0 (HER2-0, n = 109), and 1 + or IHC 2+/in situ hybridization negative (HER2-low, n = 335) receiving anthracycline and taxane-based regimens in 88.9% of cases. Most of the patients were diagnosed with stage II (67.3%) and there was no difference of disease presentation according to HER2-status. pCR was attained by 71 (16.0%) patients and was significantly associated with increased DFS (p = 0.031). Compared to HER2-0, HER2-low cases were more likely hormone receptor-positive (81.2% vs. 43.1%, p < 0.001), well-differentiated (47.5% vs. 26.6%, p = 0.001), less proliferative (21.5% vs. 8.3%, p = 0.001) and less responsive to treatment (pCR 11.6% vs. 29.4%, p < 0.0001). There was no difference in DFS according to HER2 status, though hormone-receptor (HR) negative/HER2-low cases tended to have a worse prognosis compared to HR-negative/HER2-0. By pCR achievement, 3-years DFS was 87.5.% (75.1–100%) vs. 71.6% (65.9–77.8%) (p = 0.161) in HER2-low and 89.1% (75.8–100%) vs. 72.1% (59.7–87.0%) (p = 0.092) in HER2-0.

Conclusion: Our real-world data show that HER2-low breast cancer patients represent roughly a half of the cases treated with neoadjuvant therapy, and have poor treatment response. In absence of pCR, HER2-low breast cancer patients have a dismal prognosis, especially when primary tumor hormone receptor status is negative. Studies are therefore needed to define the biology of these tumors for new therapeutic targets and to incorporate HER2-targeting agents in early-stage treatment.