Prognostic Factors in Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative (HR+/HER2-) Advanced Breast Cancer: A Systematic Literature Review

Survival Following CDK4/6 Inhibitor Therapy for Hormone Receptor-Positive, ERBB2-Negative Metastatic Breast Cancer

Importance

Endocrine therapy (ET) combined with cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) agents is the standard first-line treatment for patients with hormone receptor-positive, ERBB2 (formerly HER2 or HER2/neu)-negative metastatic breast cancer. However, optimal therapy after tumor progression to ET plus CDK4/6i remains unclear.

Objective

To evaluate progression-free survival (PFS) and overall survival (OS) in the clinical practice setting in patients with hormone receptor-positive, ERBB2-negative metastatic breast cancer following progression with ET plus CDK4/6i.

Design, Setting, and Participants

The multicenter retrospective cohort study included 506 patients diagnosed with hormone receptor-positive, ERBB2-negative metastatic breast cancer between April 22, 2015, and January 31, 2023, and who received ET-based or chemotherapy (CT)-based treatment following progression during ET plus CDK4/6i. Outcomes were analyzed based on treatment type, clinicopathologic features, and the duration of prior CDK4/6i therapy.

Main Outcomes and Measures

The primary end point was PFS in the clinical practice setting, defined as the time between the initiation of the first systemic treatment on tumor progression to ET plus CDK4/6i treatment and the detection of disease progression or patient death from any cause. The secondary end point was OS in the clinical practice setting, defined as the time interval between tumor progression during ET plus CDK4/6i treatment and patient death from any cause.

Results

In 506 women (median age at diagnosis, 52.4 [IQR, 44.6-62.8] years) diagnosed with hormone receptor-positive, ERBB2-negative metastatic breast cancer progressing during ET plus CDK4/6i, independent factors associated with poorer PFS outcomes were visceral metastases (hazard ratio [HR], 1.45; 95% CI, 1.17-1.80; P = .008) and de novo metastatic disease (HR, 1.25; 95% CI, 1.01-1.54; P = .04). A longer duration of CDK4/6i therapy (OS HR, 0.55; 95% CI, 0.41-0.73; P < .001) and an older age (PFS HR, 0.99; 95% CI 0.98-1.00; P = .03) were associated with better outcomes. Compared with oral CT, both intravenous CT- and ET-based treatments were associated with shorter PFS (intravenous CT: hazard ratio [HR], 1.45; 95% CI, 1.11-1.89; P = .006; everolimus plus exemestane: HR, 1.38; 95% CI, 1.06-1.78; P = .02; ET only: HR, 1.38; 95% CI, 1.05-1.89; P = .02). A duration of CDK4/6i treatment exceeding 12 months was associated with longer OS (HR, 0.55; 95% CI, 0.41-0.73; P < .001). Among patients with visceral metastases, intravenous CT was associated with shorter OS compared with oral CT (HR, 1.52; 95% CI, 1.03-2.24; P = .04).

Conclusions and Relevance

In this cohort study, the duration of tumor control achieved with CDK4/6i-based therapy and the presence of visceral metastases emerged as key factors that may affect treatment decision. Oral CT may offer potential benefits for specific patient subgroups.

Efficacy and Safety of Abemaciclib in Combination With Endocrine Therapy for HR+/HER2- Advanced or Metastatic Breast Cancer: A Systematic Review and Meta-Analysis

OBJECTIVES

Breast cancer, particularly the hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) subtype, remains a major global health concern. Abemaciclib, a CDK4/6 inhibitor, has shown promising results in treating advanced cases. This study comprehensively assesses the efficacy and safety of abemaciclib in combination with endocrine therapy for HR+/HER2- advanced or metastatic breast cancer.

METHODS

Following PRISMA guidelines, a systematic review and meta-analysis was conducted. A thorough literature search was conducted on PubMed, EMBASE, Cochrane Library, and ClinicalTrials.gov til December 2023. Inclusion criteria encompassed randomized controlled trials and retrospective cohort studies reporting on abemaciclib in approved doses, either as monotherapy or in combination. Outcome assessments included progression-free survival (PFS), overall response rate (ORR), side effects/adverse effects (SE/AE), and overall survival (OS). Quality assessment utilized Cochrane's revised risk of bias tool and Newcastle-Ottawa scale.

RESULTS

Pooled results of 22 studies involving 14,010 patients revealed that abemaciclib significantly improved PFS (hazard ratio=0.53; 95% CI: 0.48-0.59; P =0.00; I 2 =0%), ORR (risk ratio=2.31; 95% CI: 1.93-2.75; P =0.00; I 2 =0%), and OS (risk ratio=0.76 (95% CI: 0.65-0.87; P =0.001; I 2 =0%). However, abemaciclib increased the risk of adverse events in the fulvestrant and nonsteroidal aromatase inhibitor (NSAI) combinations, respectively.

CONCLUSIONS

Abemaciclib, particularly in combination with fulvestrant, emerges as an effective therapeutic option for HR+/HER2- advanced or metastatic breast cancer, improving PFS and OS. The higher toxicity profile warrants cautious use, especially in treatment-naive patients.

Efficacy of Sacituzumab Govitecan in Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer: A Comprehensive Systematic Review and Meta-analysis

OBJECTIVES

Breast cancer is the most diagnosed cancer in women, with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) being the predominant subtype. Sacituzumab govitecan (SG), a novel antibody-drug conjugate, has emerged as a promising treatment for metastatic HR+/HER2- breast cancer. This systematic review and meta-analysis aimed to evaluate its efficacy and safety.

METHODS

Adhering to "Preferred Reporting Items for Systematic Reviews and Meta-Analyses" guidelines, a comprehensive search was conducted in PubMed, Scopus, and Cochrane databases up to December 2023. We included clinical trials and observational studies evaluating SG in patients with HR+/HER2- advanced breast cancer. The primary outcome was progression-free survival (PFS). In contrast, the secondary outcomes included overall survival, objective response rate, clinical benefit rate, duration of response (DOR), and adverse event profiles. Review Manager (Version 5.4) was used for the statistical analysis.

RESULTS

Nine studies met the inclusion criteria for systematic review; 2 were suitable for meta-analysis. The pooled analysis showed a hazard ratio of 0.53 (95% CI: 0.34-0.83; P = 0.005; I2 = 86%) for PFSl and a hazard ratio of 0.63 (95% CI: 0.36-1.11; P = 0.11; I2 = 92%) for overall survival. The pooled analysis of the duration of response showed significant results with a standard mean difference = 0.22 (95% CI: 0.03-0.42; P = 0.02; I2 = 61%).

CONCLUSION

SG demonstrates significant benefit in PFS and duration of response in patients of HR+/HER2- advanced breast cancer.

Effect of Cyclin-Dependent Kinase 4/6 Inhibitors on Circulating Cells in Patients with Metastatic Breast Cancer

The combination of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) with endocrine therapy (ET) is the standard-of-care for estrogen receptor (ER)-positive, HER2-negative (ER+/HER2- advanced/metastatic breast cancer (mBC). However, the impact of CDK4/6i on circulating immune cells and circulating tumor cells (CTCs) in patients receiving CDK4/6i and ET (CDK4/6i+ET) remains poorly understood. This was a prospective cohort study including 44 patients with ER+/HER2- mBC treated with CDK4/6i+ET in either first or second line. Peripheral blood samples were collected before (baseline) and 3 months (t2) after therapy. Immune cell's subsets were quantified by flow cytometry, and microfluidic-captured CTCs were counted and classified according to the expression of cytokeratin and/or vimentin. Patients were categorized according to response as responders (progression-free survival [PFS] ≥ 6.0 months; 79.1%) and non-responders (PFS < 6.0 months; 20.9%). CDK4/6i+ET resulted in significant changes in the hematological parameters, including decreased hemoglobin levels and increased mean corpuscular volume, as well as reductions in neutrophil, eosinophil, and basophil counts. Specific immune cell subsets, such as early-stage myeloid-derived suppressor cells, central memory CD4+ T cells, and Vδ2+ T cells expressing NKG2D, decreased 3 months after CDK4/6i+ET. Additionally, correlations between the presence of CTCs and immune cell populations were observed, highlighting the interplay between immune dysfunction and tumor dissemination. This study provides insights into the immunomodulatory effects of CDK4/6i+ET, underscoring the importance of considering immune dynamics in the management of ER+/HER2- mBC.

Do proton pump inhibitors affect the effectiveness of cyclin-dependent kinase 4/6 inhibitors in advanced HR positive, HER2 negative breast cancer? A meta-analysis

Background

The CDK 4/6 inhibitors, including palbociclib and ribociclib, are the standard first-line treatment for hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer. Proton pump inhibitors are one of the most globally prescribed types of medications as part of the treatment for gastroesophageal reflux and heartburn complaints. Medication interactions have been demonstrated, leading to a decrease in the effectiveness of chemotherapy drugs such as capecitabine and pazopanib. However, their role and interaction with targeted therapies such as CDK inhibitors are still poorly understood.

Methods

We searched PubMed, Embase and Web of Science databases for studies that investigated the use of PPI with CDK 4/6 inhibitors versus CDK4/6 alone for advanced or metastatic breast cancer. We systematically searched for the currently available CDK inhibitors: palbociclib, ribociclib and abemaciclib. We computed hazard ratios (HRs), with 95% confidence intervals (CIs). We used DerSimonian and Laird random-effect models for all endpoints. Heterogeneity was assessed using I2 statistics. R, version 4.2.3, was used for statistical analyses.

Results

A total of 2,737 patients with advanced breast cancer in 9 studies were included, with six studies described the status menopausal as 217 (7.9%) pre-menopause and 1851 (67.6%) post-menopause, for endocrine sensitivity only five studies described1489 (54.4%) patients were endocrine-sensitive and 498 (182%) endocrine-resistent, 910 (33.2%) patients used PPIs. The overall Progression-Free Survival was in favor of the PPI non-users (HR 2.0901; 95% CI 1.410-2.9498; p < 0.001). As well as the subgroup taking palbociclib, revealing statistical relevance for the PPI non-users (HR 2.2539; 95% CI 1.3213-3.8446; p = 0.003) and ribociclib subgroup with a slight decrease in hazard ratio (HR 1.74 95% CI 1.02-2.97; p = 0.04; I2 = 40%). In the multivariate analysis, there was no statistical signifance with ECOG (HR 0.9081; 95% CI 0.4978-16566; p 0.753) and Age (HR 1.2772; 95% CI 0.8790-1.8559; p = 0.199). Either, the univariate analysis did not show statistical significance.

Conclusion

Women with HR+ and HER2-advanced metastatic breast undergoing treatment with targeted therapies, specifically CDK 4/6 inhibitors, should be monitored for the use of proton pump inhibitors. Therefore, the use of PPIs should be discussed, weighing the advantages and disadvantages for specific cases. It should be individualized based on the necessity in clinical practice for these cases.

Systematic Review Registration

identifier CRD42023484755.

Association of Neutrophil-to-Lymphocyte Ratio and Absolute Lymphocyte Count With Clinical Outcomes in Advanced Breast Cancer in the MONARCH 2 Trial

BACKGROUND

Established prognostic factors for treatment response to cyclin-dependent kinases 4 and 6 inhibitors are currently lacking. We aimed to investigate the relationship of pretreatment neutrophil-to-lymphocyte ratio (NLR) and absolute lymphocyte count (ALC) to abemaciclib outcomes.

PATIENTS AND METHODS

This was a post hoc analysis of data from MONARCH 2, a phase III study of abemaciclib or placebo plus fulvestrant in hormone-receptor positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer that progressed on endocrine therapy. Patients were divided into high and low categories based on baseline NLR (cutoff: 2.5) and ALC (cutoff: 1.5 × 109/L). The association of baseline NLR and ALC with progression-free survival (PFS) and overall survival (OS) was explored using Cox models and Kaplan-Meier estimates. Tumor response and safety were also examined.

RESULTS

NLR and ALC data were available for 645 patients (abemaciclib: N = 426; placebo: N = 219). Low-baseline NLR or high-baseline ALC was consistently associated with positive PFS and OS trends; low-baseline NLR subgroups also showed trends for better response. The abemaciclib treatment effect against placebo was observed regardless of baseline NLR or ALC. Univariate analyses showed baseline NLR and ALC were prognostic of PFS and OS. Baseline NLR remained significant in the multivariate model (P < .0001). No unexpected differences in safety were observed by baseline NLR or ALC.

CONCLUSION

Baseline NLR was independently prognostic of PFS and OS. Low-baseline NLR was associated with numerically better efficacy outcomes, but the benefit of adding abemaciclib to fulvestrant was similar irrespective of baseline NLR status.

Precise subtyping reveals immune heterogeneity for hormone receptor-positive breast cancer

A significant proportion of breast cancer cases are characterized by hormone receptor positivity (HR+). Clinically, the heterogeneity of HR+ breast cancer leads to different therapeutic effects on endocrine. Therefore, definition of subgroups in HR+ breast cancer is important for effective treatment. Here, we have developed a CMBR method utilizing computational functional networks based on DNA methylation to identify conserved subgroups in HR+ breast cancer. Calculated by CMBR, HR+ breast cancer was divided into five subgroups, of which HR+/negative epidermal growth factor receptor-2 (Her2-) was divided into two subgroups, and HR+/positive epidermal growth factor receptor-2 (Her2+) was divided into three subgroups. These subgroups had heterogeneity in the immune microenvironment, tumor infiltrating lymphocyte patterns, somatic mutation patterns and drug sensitivity. Specifically, CMBR identified two subgroups with the "Hot" tumor phenotype. In addition, these conserved subgroups were broadly validated on external validation datasets. CMBR identified the molecular signature of HR+ breast cancer subgroups, providing valuable insights into personalized treatment strategies and management options.

Prediction of clinicopathological features, multi-omics events and prognosis based on digital pathology and deep learning in HR+/HER2- breast cancer

Background

Breast cancer has the highest incidence and mortality rates among women worldwide. Hormone receptor (HR)+/human epidermal growth factor receptor 2 (HER2)- breast cancer is the most common molecular subtype, accounting for 50-79% of breast cancers. Deep learning has been widely used in cancer image analysis, especially for predicting targets related to precise treatment and patient prognosis. However, studies focusing on therapeutic target and prognosis predicting in HR+/HER2- breast cancer are lacking.

Methods

This study retrospectively collected hematoxylin and eosin (H&E)-stained slides of HR+/HER2- breast cancer patients between January 2013 and December 2014 at Fudan University Shanghai Cancer Center (FUSCC) and scanned to generate whole-slide images (WSIs). Then, we built a deep-learning-based workflow to train and validate model to predict clinicopathological features, multi-omics molecular features and prognosis; the area under the curve (AUC) of the receiver operating characteristic (ROC) and the concordance index (C-index) of the test set were used to assess model effectiveness.

Results

A total of 421 HR+/HER2- breast cancer patients were included in our study. Regarding clinicopathological features, grade III could be predicted with an AUC of 0.90 [95% confidence interval (CI): 0.84-0.97]. Regarding somatic mutations, TP53 and GATA3 mutation could be predicted with AUCs of 0.68 (95% CI: 0.56-0.81) and 0.68 (95% CI: 0.47-0.89), respectively. Regarding gene set enrichment analysis (GSEA) pathways, the G2-M checkpoint pathway was predicted with an AUC of 0.79 (95% CI: 0.69-0.90). Regarding markers of immunotherapy response, intratumoral tumor-infiltrating lymphocytes (iTILs), stromal tumor-infiltrating lymphocytes (sTILs), CD8A, and PDCD1 were predicted with AUCs of 0.78 (95% CI: 0.55-1.00), 0.76 (95% CI: 0.65-0.87), 0.71 (95% CI: 0.60-0.82), and 0.74 (95% CI: 0.63-0.85), respectively. In addition, we found that the integration of clinical prognostic variables and deep features of images can improve the stratification of patient prognosis.

Conclusions

Using a deep-learning-based workflow, we developed models to predict the clinicopathological features, multi-omics features and prognosis of patients with HR+/HER2- breast cancer using pathological WSIs. This work may contribute to efficient patient stratification to promote the personalized management of HR+/HER2- breast cancer.

Risk of Recurrence in Patients with HER2+ Early-Stage Breast Cancer: Literature Analysis of Patient and Disease Characteristics

Human epidermal growth factor receptor 2 (HER2) overexpression occurs in 15% to 20% of patients with early-stage breast cancers (EBCs). Without HER2-targeted therapy, 30% to 50% of patients relapse within 10 years, many developing incurable metastatic disease. This literature review was designed to identify and validate patient- and disease-related factors associated with recurrence in patients with HER2+ EBC. Peer-reviewed primary research articles and congress abstracts were identified by searching MEDLINE. Articles published in English from 2019 to 2022 were included to identify contemporary treatment options. Results were analyzed for the relationship between risk factors and surrogates of HER2+ EBC recurrence to determine how identified risk factors affected HER2+ EBC recurrence. Sixty-one articles and 65 abstracts that assessed age at diagnosis, body mass index (BMI), tumor size at diagnosis, hormone receptor (HR) status, pathologic complete response (pCR) status, and biomarkers were analyzed. We confirmed the results of previously published reviews reporting residual cancer burden >0, non-pCR, and fewer tumor-infiltrating lymphocytes (TILs) as risk factors of recurrence. HR status remained an important risk factor for recurrence, with HER2+/HR+ disease more likely to recur. Two or more positive lymph nodes, higher BMI, larger primary tumor size, and low Ki67 were more commonly associated with HER2+ EBC recurrence. The identification of patient and disease factors frequently associated with HER2+ EBC recurrence in the literature provides insight into potential recurrence risk factors. Further investigation into the risk factors identified in this review could lead to improved treatments for patients at high risk for HER2+ EBC recurrence.

Pretreatment neutrophil to lymphocyte ratio as prognostic factor in metastatic breast cancer treated with cyclin dependent kinase 4/6 inhibitors

Background

Cyclin dependent kinase inhibitors (CdK4/6i) changed the course of hormone receptor positive (HR+) HER2 negative (HER2-) metastatic breast cancer (mBC). To date, no factors have been shown to predict response to CdK4/6i. Neutrophil-to-lymphocyte ratio (NLR), an indicator of the host systemic inflammatory response, is an independent prognostic factor for survival in cancers. We conducted this study to evaluate the impact of NLR on survival in mBC patients treated with first line CdK4/6i.

Methods

All mBC patients treated with first line CdK4/6i between November 2015 and December 2019 were retrospectively included. The biomarker threshold was defined using ROC curves. We analyzed progression free survival (PFS), overall survival (OS), 12-month PFS and response rate according to NLR in univariable and multivariable analysis.

Results

A total of 126 patients treated with palbociclib (n=101), ribociclib (n=18) or abemaciclib (n=7) were included, with a median follow-up of 33 months [range: 2.9-57]. Median age was 65 years [29-86], 40% patients had good performance status (ECOG-PS 0). Most patients (71%) were included at the metastatic relapse stage and 29% had only bone metastases. Median PFS and median OS were 27 and 51 months, respectively. High NLR (≥ 2.53) was significantly associated with worse PFS (Hazard Ratio (HR)=0.50, CI_95% = [0.32-0.79]) and worse OS (HR=0.45, [CI_95%: 0.23-0.87]). In multivariable analysis, NLR and ECOG PS were independently factors associated with PFS (p=0.016 and p=0.001, respectively).

Conclusion

High NLR was associated with worse PFS and OS in HR+ HER2- mBC patients treated with first line CdK4/6i. NLR is a reliable and inexpensive prognostic marker, easily accessible in routine clinical practice, which could help optimize the therapeutic strategy. These results need to be confirmed in larger prospective studies.

Real-world study of overall survival with palbociclib plus aromatase inhibitor in HR+/HER2- metastatic breast cancer

Data on real-world effectiveness of cyclin-dependent kinase 4/6 inhibitor combination therapy versus endocrine therapy alone are limited. The Flatiron Health Analytic Database was used to assess overall survival (OS) in patients with hormone receptor–positive/human epidermal growth factor receptor 2–negative (HR+/HER2−) metastatic breast cancer (MBC) treated with first-line palbociclib plus an aromatase inhibitor (AI) versus an AI alone in routine US clinical practice. In total, 2888 patients initiated treatment during February 3, 2015–March 31, 2020, with a potential ≥6-month follow-up (cutoff date, September 30, 2020). After stabilized inverse probability treatment weighting, median OS (95% CI) is significantly longer among palbociclib versus AI recipients (49.1 [45.2–57.7] versus 43.2 [37.6–48.0] months; hazard ratio, 0.76 [95% CI, 0.65–0.87]; P < 0.0001). Progression-free survival (95% CI) is 19.3 (17.5–20.7) versus 13.9 (12.5–15.2) months, respectively (hazard ratio, 0.70 [95% CI, 0.62–0.78]; P < 0.0001). These data support first-line palbociclib plus an AI treatment for HR+/HER2− MBC.

(Trial number NCT05361655).

Clever-1 positive macrophages in breast cancer

Purpose

Common Lymphatic Endothelial and Vascular Endothelial Receptor 1 (Clever-1) is expressed by a subset of immunosuppressive macrophages and targeting the receptor with therapeutic antibodies has been shown to activate T-cell-mediated anti-cancer immunity. The aim of this research was to study Clever-1 expression in breast cancer. Specifically, how Clever-1 + macrophages correlate with clinicopathologic factors, Tumor Infiltrating Lymphocytes (TILs) and prognosis.

Methods

Tissue microarray blocks were made from 373 primary breast cancer operation specimens. Hematoxylin and Eosin (H&E-staining) and immunohistochemical staining with Clever-1, CD3, CD4 and CD8 antibodies were performed. Differences in quantities of Clever-1 + macrophages and TILs were analyzed. Clever-1 + cell numbers were correlated with 25-year follow-up survival data and with breast cancer clinicopathologic parameters.

Results

Low numbers of intratumoral Clever-1 + cells were found to be an independent adverse prognostic sign. Increased numbers of Clever-1 + cells were found in high grade tumors and hormone receptor negative tumors. Tumors that had higher amounts of Clever-1 + cells also tended to have higher amounts of TILs.

Conclusion

The association of intratumoral Clever-1 + macrophages with better prognosis might stem from the function of Clever as a scavenger receptor that modulates tumor stroma. The association of Clever-1 + macrophages with high number of TILs and better prognosis indicates that immunosuppression by M2 macrophages is not necessarily dampening adaptive immune responses but instead keeping them in control to avoid excess inflammation.

Early stage breast cancer follow-up in real-world clinical practice: the added value of cell free circulating tumor DNA

Purpose

Physical examinations and annual mammography (minimal follow-up) are as effective as laboratory/imaging tests (intensive follow-up) in detecting breast cancer (BC) recurrence. This statement is now challenged by the availability of new diagnostic tools for asymptomatic cases. Herein, we analyzed current practices and circulating tumor DNA (ctDNA) in monitoring high-risk BC patients treated with curative intent in a comprehensive cancer center.

Patients and methods

Forty-two consecutive triple negative BC patients undergoing neoadjuvant therapy and surgery were prospectively enrolled. Data from plasma samples and surveillance procedures were analyzed to report the diagnostic pattern of relapsed cases, i.e., by symptoms, follow-up procedures and ctDNA.

Results

Besides minimal follow-up, 97% and 79% of patients had at least 1 non-recommended imaging and laboratory tests for surveillance purposes. During a median follow-up of 5.1(IQR, 4.1–5.9) years, 13 events occurred (1 contralateral BC, 1 loco-regional recurrence, 10 metastases, and 1 death). Five recurrent cases were diagnosed by intensive follow-up, 5 by symptoms, and 2 incidentally. ctDNA antedated disseminated disease in all evaluable cases excepted two with bone-only and single liver metastases. The mean time from ctDNA detection to suspicious findings at follow-up imaging was 3.81(SD, 2.68), and to definitive recurrence diagnosis 8(SD, 2.98) months. ctDNA was undetectable in the absence of disease and in two suspected cases not subsequently confirmed.

Conclusions

Some relapses are still symptomatic despite the extensive use of intensive follow-up. ctDNA is a specific test, sensitive enough to detect recurrence before other methods, suitable for clarifying equivocal imaging, and exploitable for salvage therapy in asymptomatic BC survivors.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00432-022-03990-7.

Transmembrane 4 L Six Family Member 1 Suppresses Hormone Receptor--Positive, HER2-Negative Breast Cancer Cell Proliferation

Background: The prognosis of breast cancer varies according to the molecular subtype. Transmembrane 4 L six family 1 (TM4SF1) exhibits different expression patterns among the molecular subtypes of breast cancer. However, the expression profile of TM4SF1 in hormone receptor HR⁺HER2^- breast cancer remains unclear.

Methods: TM4SF1 mRNA levels were examined in major subclasses of breast cancer by analyzing The Cancer Genome Atlas (TCGA) datasets. In addition, TM4SF1 protein and mRNA levels in HR⁺HER2^- breast cancer tissue samples were determined by immunohistochemistry and Western blot assay. The effect of TM4SF1 on cell proliferation was evaluated using MTT, colony formation, 3D organoid, and xenograft models, following the TM4SF1 overexpression or knockdown.

Results: TCGA database analysis demonstrated that TM4SF1 was downregulated in breast cancer compared with the healthy adjacent breast tissue. In addition, the expression of TM4SF1 in basal-like one and the mesenchymal TNBC tissue was higher than that of the healthy adjacent breast tissue. Other types, including the luminal androgen receptor–positive TNBC tissue, expressed lower levels of TM4SF1. Immunohistochemistry and real-time quantitative PCR assays demonstrated that the TM4SF1 protein and mRNA levels were downregulated in the HR⁺HER2^- breast cancer tissue compared with the healthy adjacent tissue. Moreover, the TM4SF1 overexpression reduced the viability of MCF-7 and ZR-75-1 breast cancer cells, whilst reducing the number of colonies and 3D-organoids formed by these cell lines. By contrast, TM4SF1 knockdown led to an increased MCF-7 cell proliferation. However, in the TNBC cell line, MDA-MB-231, TM4SF1 silencing reduced cell proliferation. In vivo, the TM4SF1 overexpression inhibited MCF-7 xenograft growth in a nude mouse model, which was associated with the downregulation of the Ki-67 expression, apoptosis induction, and inhibition of the mTOR pathway.

Conclusion: TM4SF1 is downregulated in HR + HER2-breast cancer, and the overexpression of TM4SF1 suppresses cell proliferation in this cancer subtype.