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

Efficacy and Safety of Cyclin-Dependent Kinase 4/6 Inhibitors in Patients with Breast Cancer: A Systematic Review and Meta-analysis of Randomized Controlled Trials and Real-World Studies

BACKGROUND

The efficacy and safety of cyclin-dependent kinase (CDK)4/6 inhibitors in patients with breast cancer have been investigated by large-scale trials sponsored by drug companies. A lack of real-world evidence may lead to biases.

OBJECTIVE

We systematically reviewed the large-scale clinical trials and real-world data to investigate the efficacy and safety of CDK4/6 inhibitors in patients with breast cancer.

PATIENTS AND METHODS

We searched PubMed, Embase, and Cochrane Library from the inception of each database to January 2024. We included both prospective and retrospective studies reporting the survival outcomes or adverse effects of CDK4/6 inhibitors in patients with breast cancer.

RESULTS

We included 41 prospective trials and 80 retrospective studies involving a total of 69,535 patients. Our meta-analysis of double-arm studies revealed that all types of CDK4/6 inhibitors significantly improved overall survival and progression-free survival. The pooled estimates of the 1-year overall survival (OS) rates and 1-year progression-free survival (PFS) rates in single-arm real-world studies were 74.8% and 49.4% for abemaciclib, 84.1% and 55.7% for palbociclib, and 93.4% and 62.2% for ribobiclib, respectively. In terms of adverse effects, Asian patients were significantly more likely to experience neutropenia and increased alanine aminotransferase, whereas Western patients were significantly more likely to have grade 3 or 4 adverse effects and constipation.

CONCLUSIONS

CDK4/6 inhibitors can improve OS and PFS in patients with advanced breast cancer. The incidence of adverse effects may differ with drugs and with ethnicity. On the basis of our findings, clinicians can select suitable CDK4/6 inhibitors for patients by conducting thorough clinical evaluations.

Large Unstained Cells (LUC): A Novel Predictor of CDK4/6 Inhibitor Outcomes in HR+ HER2-Negative Metastatic Breast Cancer

Background: Although CDK4/6 inhibitors combined with endocrine therapies have improved outcomes in HR+ HER2-negative metastatic breast cancer, predictive biomarkers for treatment response and adverse effects remain limited. This study assessed the prognostic and predictive value of large unstained cells (LUC), a subset of white blood cells that may reflect immune status or treatment response. Methods: A retrospective analysis of 210 patients with HR+ HER2-negative metastatic breast cancer treated with CDK 4/6 inhibitors between 2021 and 2024 was conducted. Clinical data, including demographics, tumor characteristics, and treatment regimens, were analyzed. Based on LUC levels, progression-free survival (PFS), overall survival (OS), and adverse events were evaluated. Results: The cohort had a median age of 57, of which 78% were postmenopausal. Common metastatic sites included bone (67%) and liver (24%). At a median follow-up of 18.5 months, the PFS and OS rates were 65% and 83%. Patients with low LUC levels had significantly shorter PFS (OR: 1.91; p = 0.014) and OS (OR: 2.39; p = 0.012), while high LUC levels correlated with a lower incidence of grade 3 neutropenia (OR: 0.49; p = 0.017). Liver metastasis and prior treatments were also linked to shorter survival. Conclusions: LUC levels emerge as a promising biomarker for predicting survival outcomes and the risk of neutropenia in HR+ HER2-negative metastatic breast cancer patients treated with CDK 4/6 inhibitors and endocrine therapy, showing their potential to guide personalized treatment approaches.

First-line carboplatin-based chemotherapy may be beneficial for HER2-low advanced breast cancer: A retrospective analysis

For patients with human epidermal growth factor receptor 2 (HER2)-low advanced breast cancer who had failed to meet with anthracycline or taxane, the application of HER2-targeted antibody-drug conjugates as second-line therapy could improve patients' outcomes, but it is unclear whether carboplatin-based first-line therapy will benefit these patients. This retrospective study was designed to explore whether carboplatin based first-line treatment could improve outcomes in HER2-low advanced breast cancer, and to analyze potential factors affecting efficacy and prognosis. 103 patients with HER2-negative metastatic breast cancer were treated with carboplatin based first-line therapy. The differences in progression-free survival (PFS), objective response rate (ORR), and adverse events were analyzed in different HER2 expression subgroups. The risk ratio (HR) and 95% confidence interval (CI) for PFS were estimated using Cox proportional risk models. The ORR for the whole group was 42.72% and the median PFS (mPFS) was 7.93 months (m). The ORR of HER2-low patients was significantly higher than HER2-zero patients (56.4% vs 27.1%, P = .003), and HER2-zero was an independent risk factor of ORR (OR 3.478, 95%CI 1.516-7.977, P = .003), especially in the HR-negative subgroup. The mPFS was significantly longer in patients with low neutrophil-to-lymphocyte ratio (NLR) scores than those with high NLR scores (P < .001). Multivariate analysis showed that young breast cancer (age < 40) (P = .006) and high NLR values (P = .001) were prognostic risk factors affecting mPFS. The main grade 3 to 4 adverse reactions were neutropenia (15.53%), anemia (15.53%), and leukopenia (11.65%). The first-line carboplatin-based chemotherapy is quite active and tolerable in patients with HER2-low advanced breast cancer, that higher response rates can be achieved. In cases where CDK4/6 inhibitors are inappropriate for use due to resistance to endocrine therapy or the urgent need for short-term clinical response, chemotherapy remains important. When it is necessary to consider the accessibility of antibody-drug conjugates and the economics of patients, carboplatin-based chemotherapy may be provided to HER2-low patients as a more convenient, cost-effective and efficient option on the front line. Forecasting the efficacy and prognosis via inflammatory index such as NLR before the commencement of the treatment could enhance the precision and efficiency of carboplatin-based regimens.

A therapeutic algorithm guiding subsequent therapy selection after CDK4/6 inhibitors' failure: A review of current and investigational treatment for HR+/Her2- breast cancer

The first-line combination therapies utilizing cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) with endocrine therapy (ET) have significantly impacted the course of hormone receptor positive (HR+)/Human Epidermal Growth Factor Receptor 2 negative (HER2-) advanced breast cancer (ABC). However, resistance often emerges, leading to a molecularly different disease. Estrogen receptor one (ESR1) gene mutations, driving resistance to aromatase inhibitors (AIs), may guide the use of fulvestrant or emerging oral selective estrogen receptor degraders (SERDs) like elacestrant. The dynamic nature of ESR1 mutations suggests potential guidance for continuing CDK4/6i therapy beyond progression. Targeting mutations like breast cancer gene 1 and 2 (BRCA 1/2) with Poly (ADP-ribose) polymerase (PARP) inhibitors or the PI3K/AKT/mTOR pathway provides therapeutic options. The advent of antibody-drug conjugates (ADCs) like trastuzumab deruxtecan (T-DXd) and novel agents targeting Trophoblast cell surface antigen-2 (Trop-2) introduces further complexity, underscoring the need for early intervention targeting specific genomic alterations in metastatic BC.

Timing of Dose Reductions and Survival Outcomes in Metastatic Breast Cancer Patients Treated with Cyclin-Dependent Kinase 4/6 Inhibitors

BACKGROUND/OBJECTIVES

Dose reductions in CDK4/6 inhibitors, such as ribociclib and palbociclib, are often necessary due to treatment-related toxicities in patients with advanced breast cancer. This study aims to evaluate the impact of the timing of dose reductions on progression-free survival (PFS) and overall survival (OS) in a real-world cohort.

METHODS

This single-center, retrospective study included patients treated with ribociclib or palbociclib between 2019 and 2023 at a cancer center in Turkey. Dose reductions due to drug-related toxicities were recorded, and survival outcomes were analyzed. Patients were categorized based on the timing of dose reductions: within the first 3 months (early) and after 3 months (late).

RESULTS

Among 392 patients (mean age 57.13 years), 16.8% had dose reductions within 3 months, 21.7% had late dose reductions, and 61.5% had no dose reductions. The mPFS was 14.26 months for early dose reductions, 33.12 months for late dose reductions, and 20.6 months for no dose reductions (p < 0.001). The mOS was 37.12 months for early dose reductions, not reached for late dose reductions, and 57.76 months for no dose reductions (p < 0.001). Hematological toxicity, primarily neutropenia, was the most common cause of dose reductions. The ECOG performance status, line of therapy, and CDK4/6 inhibitor type were also significant predictors of PFS and OS.

CONCLUSIONS

Early dose reductions in CDK4/6 inhibitors negatively affect PFS and OS, highlighting the importance of maintaining treatment intensity in the first 3 months. However, late dose reductions do not negatively affect progression-free survival (PFS) or overall survival (OS), with late dose reductions associated with better outcomes. Prospective studies in larger patient populations will further clarify our knowledge on this subject.

Prognosis in HR-positive metastatic breast cancer with HER2-low versus HER2-zero treated with CDK4/6 inhibitor and endocrine therapy: a meta-analysis

Background

The combination of CDK4/6 inhibitors (CDK4/6i) and endocrine therapy (ET) is currently the standard first-line treatment for patients with metastatic hormone receptor positive (HR+), and HER2-negative (HER2-) breast cancer. However, the impact of HER2 status on the prognosis of patients receiving CDK4/6i and ET remains unclear. The meta-analysis was conducted to evaluate different outcomes between HER2-low and HER2-zero patients in advanced HR+ breast cancer receiving CDK4/6i and ET.

Methods

A systematic search was performed in PubMed and EMBASE databases for relevant published literature. Objective response rate (ORR), overall survival (OS), and progression-free survival (PFS) were pooled by fixed or random effects models.

Results

Overall, 12 studies with 3567 patients were eligible for analysis. The pooled analysis suggested that no significant differences were observed in terms of ORR and OS between HER2-low and HER2-zero patients who underwent CDK4/6i and ET. Similarly, no significant difference in PFS was found between HER2-low and HER2-zero patients who underwent post-line CDK4/6i and ET or first-line Palbociclib and ET. However, in patients who received mixed-line (not a single treatment line) or first-line CDK4/6i and ET, the PFS was significantly shorter in the HER2-low subgroup than in the HER2-zero subgroup (mixed-line: HR = 1.36; 95% CI = 1.11-1.65; P = 0.002; first-line: HR = 1.14; 95% CI = 1.01-1.28; P = 0.04). A similar phenomenon was observed in patients who received mixed-line or post-line Palbociclib and ET (mixed-line: HR = 1.60; 95% CI = 1.09-2.34; P = 0.02; post-line: HR = 1.43; 95% CI = 1.03-2.00; P = 0.03).

Conclusion

These results indicated that HER2-low status did not have a significant association with ORR and OS, but it may have a worse impact on PFS in patients who received mixed-line or first-line CDK4/6i and ET, as well as mixed-line or post-line palbociclib plus ET.

The impact of human epidermal growth factor receptor-2 (low) status on the efficacy of first line cyclin-dependent kinase 4/6 inhibitors in advanced breast cancer

The fact that the human epidermal growth factor receptor 2 (HER2)-low group, historically classified as HER2 negative in breast cancer histology, benefited from HER2-targeted treatments similarly to the HER2-positive group indicates that this group has a distinct histology from the HER2-0 group. The effectiveness of cyclin-dependent kinase 4/6 inhibitors, which are the standard first-line treatment for hormone receptor-positive, HER2-negative advanced breast cancer, in this newly defined histological subgroup remains a topic of debate. In our study, we examined the impact of HER2 status on the efficacy of CDK4/6 inhibitors. Our study is a retrospective, multicenter, real-world data analysis. One hundred sixty patients were included in the study. The relationship between HER2 status and other clinical-pathological features, as well as progression-free survival, was examined. Median follow-up was 20.33 ± 0.98 months. The mPFS could not be reached. All patients exhibited positive estrogen receptor expression. Among the patients, 111 (69.4%) were categorized as HER2-0, and 49 (30.6%) as HER2-low. The 24-month progression-free survival rates were similar between HER2-0 and HER2-low patients (60.6% vs 65.3%, hormone receptor: 1.18, CI: 0.67-2.20, P = .554). We established that the mPFS achieved with cyclin-dependent kinase 4/6 inhibitors as a first-line therapy for patients with advanced breast cancer is unaffected by HER2 status.

Relationship between HER2-low status and efficacy of CDK4/6 inhibitors in advanced breast cancer: a real-world study

AIMS AND OBJECTIVES

Human epidermal growth factor receptor 2 (HER2)-low breast cancer (BC) is a new entity considered a biologically distinct subtype from HER2-zero BC. However, the importance of HER2 low expression on the activity of cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) remains unclear.

METHODS/MATERIALS

We conducted a single-center retrospective study including hormone receptor-positive (HR +) /HER2- metastatic BC (mBC) patients treated with CDK4/6i plus endocrine treatment (ET) as first-line therapy. Clinical outcomes were analyzed according to HER2 expression.

RESULTS

258 women were analyzed with a median follow-up of 25.4 months; 39.9% had HER2 low, and 60.1% had HER2 zero BC. Median progression-free survival (mPFS) in the HER2-low group was 27.6 months compared with 44.3 months in the HER2-zero group (p = 0.341). In patients receiving ribociclib, the mPFS in the HER2-low group was 24.2 months compared with 53.1 months in the HER2-zero group (multivariate-adjusted HR: 1.981, 95 Cl 1.094-3.586; p = 0.024). The survival probabilities at 24, 36 and 48 months for the HER2 low and HER2 zero groups were 82%, 69%, 69% and 83%, 75% and 69%, respectively (p = 0.336). Objective response rate (p = 0.179) and disease control rate (p = 0.338) did not significantly differ between HER-2-low and HER-2-zero groups.

CONCLUSIONS

The mPFS in the Her2-zero group was almost twice that of the Her2-low group, but the difference was not statistically significant. mPFS was significantly longer in the HER2-zero group compared to the HER2-low group in patients receiving ribociclib. More prospective studies are needed to understand the actual consequences of this biomarker.

The effects of low HER2 expression on survival in patients with metastatic breast cancer treated with CDK 4/6 inhibitors: a multicenter retrospective study

PURPOSE

Endocrine therapy (ET) in combination with CDK 4/6 inhibitors (CDK 4/6i) is the standard treatment modality for hormone receptor (HR)-positive and HER2-negative metastatic breast cancer (mBC). There is uncertainty about the prognostic and predictive value of HER2-low status and whether HER2-low BC is an individual biologic subtype. In this study, we aimed to investigate the prognostic effect of HER2 expression status on survival in mBC patients treated with first-line ET plus CDK 4/6i.

METHODS

This multicenter retrospective study included patients with HR + /HER2-negative mBC cancer who were treated with first-line CDK 4/6i in combination with ET from January 2016 to March 2023. Patients were divided into two groups (HER2-low and zero), and survival and safety analyses were performed.

RESULTS

A total of 201 patients were included in this study; of these, 73 (36.3%) had HER2-low disease and 128 (63.7%) had HER2-zero. There were 135 patients (67.2%) treated with ribociclib and 66 (32.8%) with palbociclib. Most of the patients (75.1%) received aromatase inhibitors as combination-endocrine therapy. Baseline characteristics were similar between the two groups. The median follow-up was 19.1 months (range: 2.5-78.4). The most common side effect was neutropenia (22.4%). The frequency of grade 3-4 toxicity was similar between the HER2-zero and low patients (32% vs 31.5%; p = 0.939). Visceral metastases were present in 44.8% of patients. Between the HER2-low and zero groups, median PFS (25.2 vs 22.6 months, p = 0.972) and OS (not reached vs 37.5 months, p = 0.707) showed no statistically significant differences.

CONCLUSION

The prognostic value of HER2-low status remains controversial. Our study showed no significant effect of HER2 low expression on survival in patients receiving CDK 4/6i plus ET.

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.