CDK4/6 inhibition in early and metastatic breast cancer: A review

Breast cancer (BC) is responsible for 14% of cancer-related deaths in women [1]. Cyclin-dependent kinase (CDK) 4/6 inhibitors are a new class of selective drugs, offering an effective and tolerable treatment. CDK4/6 inhibitors induce cell cycle arrest in the G1 phase, and may thereby prevent tumour progression. Three CDK4/6 inhibitors have been tested in clinical BC trials: palbociclib, ribociclib, and abemaciclib. The Food and Drug Administration (FDA) and European Commission (EMA) have approved palbociclib for the treatment of patients HR+ HER2- locally advanced or metastatic BC (aBC) in combination with an aromatase inhibitor as initial therapy in postmenopausal women or in combination with fulvestrant in women who have received prior endocrine therapy. Ribociclib has been approved by the FDA in combination with an aromatase inhibitor as initial therapy for postmenopausal women with HR+ HER2- aBC. Moreover, CDK4/6 inhibitors have shown promising results in the (neo)adjuvant setting. In this review, the principal completed and ongoing clinical trials in aBC are reviewed for both the metastatic as (neo)adjuvant setting. Tables will provide a complete overview of the ongoing clinical trials. At last, the future perspectives of these CDK4/6 inhibitors are discussed.     

CDK4/6 Inhibition as a therapeutic strategy in breast cancer: palbociclib,ribociclib, and abemaciclib

With 40,920 American women expected to die from breast cancer in 2018 and global health estimates that more than 508,000 women died in 2011 from this disease, the identification of novel therapeutic strategies for the treatment of breast cancer cannot be ignored. A breakthrough class of cancer drugs that has emerged in recent years and has had an impact in the treatment of breast cancer are the cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, with palbociclib the first in class to have received regulatory approval for breast cancer. In this article we will compare and contrast three CDK4/6 inhibitors - palbociclib, ribociclib and abemaciclib - that have received regulatory approval for the treatment of metastatic breast cancer. Ribociclib and abemaciclib developed after the success of palbociclib represent examples of "me-too" therapies increasingly being deployed in oncology.     

Fatigue,alopecia and stomatitis among patients with breast cancer receiving cyclin-dependent kinase 4 and 6 inhibitors: a systematic review and meta-analysis

Background: Cyclin-dependent kinase (CDK) inhibitors emerge as efficacious agents in hormone positive metastatic breast cancer with more acceptable toxicity profiles than cytotoxic chemotherapy. However, some adverse effects such as fatigue, alopecia and stomatitis, vastly concern patients.

Methods: The search was conducted in PubMed, American Society of Clinical Oncology meeting library, European Society for Medical Oncology meeting abstract, and the San Antonio meeting abstract databases. We identified phase 2 or 3 trials recruiting patients with breast cancer, randomized to receive hormonal treatment plus either CDK4/6 inhibitors or placebo. We considered studies providing incidence of fatigue, alopecia and stomatitis relevant.

Results: One thousand records were screened. 34 studies were considered relevant. Four studies were found to be eligible for meta-analysis with a total of 2007 patients. The relative risk for all grade fatigue was 1.34 [95% CI: 1.17–1.54, p < 0.0001], for all grade alopecia was 2.14 [95% CI: 1.23–3.73, p = 0.007], and for all grade stomatitis 4.87 [95% CI: 2.11–11.24, p = 0.0002]. In addition, the relative risk for high grade fatigue was 2.40 [95% CI: 1.10–5.26, p = 0.03].

Conclusion: CDK4/6 inhibitors were associated with an increased risk of fatigue, alopecia and stomatitis. Further studies with self-reported questionnaires may elucidate the impact of the increased risk of these selected adverse effects on the patients’ quality of life.     

Arthralgia induced by endocrine therapy with or without cyclin-dependent kinase 4/6 inhibitors in breast cancer: A systematic review and meta-analysis

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) have been approved for breast cancer (BC) treatment. Several trials suggested that arthralgia was reduced in patients treated with ET plus CDK4/6i compared with that in those with ET-alone. We aimed to compare arthralgia rates in BC patients treated with/without CDK4/6i. We reviewed randomized controlled phase II/III trials investigating CDK4/6i with ET in hormone receptor-positive and epidermal growth factor 2-negative BC. Publications were retrieved from PubMed from January 2014 to April 2021. We compared arthralgia rates between patients who were administered ET plus CDK4/6i (CDK4/6i group) and those treated with ET-alone (control group). We reviewed 12 trials that reported data on adverse effects for arthralgia. These trials included 17,440 patients (9255 in the CDK4/6i group and 8185 in the control group). The arthralgia rate in the CDK4/6i group was significantly lower than that in the control group (27.6% vs. 34.8%, p < .001), especially in early BC (28.8% vs. 37.3%, p < .001). These suggested that the arthralgia rate in patients treated with ET plus CDK4/6i was lower than that in patients treated with ET-alone and that CDK4/6i may decrease the arthralgia rate in BC patients treated with ET, especially in early BC.     

CDK4/6抑制剂在激素受体阳性进展期乳腺癌治疗中的研究进展

内分泌治疗因其兼具良好的疗效及安全性,是激素受体阳性进展期乳腺癌患者的重要治疗手段。近年来内分泌领域进展迅速,很多新型药物相继出现,其中包括多种可以逆转或延迟内分泌耐药的周期蛋白依赖性激酶(cyclin-dependent kinase,CDK)4/6抑制剂。CDK4/6抑制剂联合内分泌治疗可为激素受体阳性进展期乳腺癌患者带来生存获益、延迟至化疗时间,正逐渐改变国内外激素受体阳性进展期乳腺癌的治疗模式。本文将就CDK4/6抑制剂在激素受体阳性进展期乳腺癌中的治疗进展进行综述。     

Molecular mechanisms of resistance to CDK4/6 inhibitors in breast cancer: A review

Deregulation of the cyclin D-CDK4/6-INK4-RB pathway leading to uncontrolled cell proliferation, is frequently observed in breast cancer. Currently, three selective CDK4/6 inhibitors have been FDA approved: palbociclib, ribociclib and abemaciclib. Despite promising clinical outcomes, intrinsic or acquired resistance to CDK4/6 inhibitors has limited the success of these treatments; therefore, the development of various strategies to overcome this resistance is of great importance. We highlight the various mechanisms that are directly or indirectly responsible for resistance to CDK4/6 inhibitors, categorizing them into two broad groups; cell cycle-specific mechanisms and cell cycle-nonspecific mechanisms. Elucidation of the diverse mechanisms through which resistance to CDK4/6 inhibitors occurs, may aid in the design of novel therapeutic strategies to improve patient outcomes. This review summarizes the currently available knowledge regarding mechanisms of resistance to CDK4/6 inhibitors, and possible therapeutic strategies that may overcome this resistance as well.     

CDK4/6抑制剂联合mTOR抑制剂在乳腺癌中的作用机制

CDK-RB-E2F通路和PI3K-AKT-mTOR通路对乳腺癌耐药机制起到了关键作用。通过对两个通路的研究发现,在治疗激素受体阳性的乳腺癌时,CDK4/6抑制剂与内分泌药物联合使用可以提高患者的生存率,mTOR抑制剂也显示出抗肿瘤的实力。最近的研究表明,mTOR抑制剂和CDK4/6抑制剂联合使用可以进一步抑制CDK-RB-E2F通路激活,协同控制肿瘤细胞增殖。同时发现CDK4/6抑制剂耐药患者的CDK-RB-E2F通路重新激活,仍对mTOR抑制剂敏感。还有研究表明CDK4/6抑制剂和mTOR抑制剂可以通过自噬作用协同控制肿瘤的发生。本文针对两药联合在乳腺癌中的作用机制进行综述。     

Drug-drug interactions in breast cancer patients treated with CDK4/6 inhibitors

CDK4/6 inhibitors are a new class of anticancer drugs used for the treatment of women with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced or metastatic breast cancer with disease progression following endocrine therapy. Polypharmacy is a well-known problem in advanced cancer causing potential drug-drug interactions (DDIs), which, in turn, may limit the therapeutic value of CDK4/6 inhibitors. Therefore, understanding the mechanisms underlying potential DDIs in patients taking CDK4/6 inhibitors may be useful in decision-making processes and represent an important step towards treatment personalization. The present review is aimed at describing the potential DDIs that might occur in breast cancer patients receiving CDK4/6 inhibitors based on direct evidence from the literature and mechanistic considerations tailored on specific class of drugs used in combination.     

CDK4/6抑制剂治疗三阴性乳腺癌的研究进展

细胞周期的调控机制在肿瘤的发生、发展中发挥着重要作用。多项研究表明,在雌激素受体阳性、人类表皮生长因子受体阴性的乳腺癌患者中,细胞周期蛋白依赖性激酶4/6（cyclin-dependent kinase 4/6,CDK4/6）抑制剂具有较好的疗效,然而其在三阴性乳腺癌患者中的疗效仍需进一步探讨。Cyclin D-CDK4/6-INK4-Rb-E2F信号通路因具有调控细胞周期检查点的作用,被认为是乳腺癌潜在的治疗靶点。寻找三阴性乳腺癌与CDK4/6抑制剂关联的生物标志物,探究合理的药物配伍,筛选能从中获益的靶向人群,对临床工作具有重要意义。对CDK4/6抑制剂在三阴性乳腺癌的研究进展进行综述,探讨其应用前景及优化手段。     

CDK4/6抑制剂在乳腺癌治疗中的研究进展

细胞增殖、生长和分裂等过程受到细胞周期的严格调控,其调控机制在肿瘤的发生发展中发挥重要作用。近年来,多项研究显示,细胞周期蛋白依赖性激酶4和6（CDK4/6）抑制剂对于雌激素受体阳性或人类表皮生长因子受体阳性的乳腺癌患者具有较好的疗效,然而其在三阴性乳腺癌患者中的作用仍存在争议,故探究相关分子标志物以进一步筛选最能从该治疗中获益的乳腺癌人群对临床具有重要意义。此外视网膜母细胞瘤基因（Rb）也在乳腺癌中扮演关键角色,而cyclin D-CDK4/6-Rb信号通路因具有调控细胞周期限制点的作用,被认为是乳腺癌潜在的治疗靶点。本文将对CDK4/6抑制剂在乳腺癌治疗中的研究进展作一综述。     

Mechanisms of therapeutic CDK4/6 inhibition in breast cancer

Cyclin dependent kinase (CDK) 4/6 inhibitors have advanced the treatment of metastatic breast cancer by targeting the cell cycle machinery, interrupting intracellular and mitogenic hormone signals that stimulate proliferation of malignant cells. Preclinical evidence demonstrated that derangements of cyclin D1, CDK4/6, and retinoblastoma expression are common in breast cancer, and suggested a therapeutic benefit from interrupting this axis required for cell cycle progression. Studies of cell lines and animal models of breast cancer have demonstrated the complex interplay between the cell cycle and estrogen receptor and human epidermal growth receptor 2 signaling, which informs our understanding of synergistic use of CDK4/6 inhibitors with endocrine therapy, as well as mechanisms of resistance to endocrine therapy. Interestingly, estrogen receptor activity leads to upregulation of cyclin D1 expression, but the estrogen receptor is also in turn activated by cyclin D1, independent of estrogen binding. Early CDK inhibitors were nonspecific and limited by systemic toxicities, while the current generation of CDK4/6 inhibitors have shown promise in the treatment of hormone receptor-positive breast cancer. Preclinical investigations of the three CDK4/6 inhibitors approved by the US Food and Drug Administration (palbociclib, ribociclib, and abemaciclib) lend further insight into their mechanism of action, which will hopefully inform the future use and refinement of these therapies. Finally, we summarize evidence for additional novel CDK4/6 inhibitors currently in development.     

Outcomes and toxicity of concurrent CDK4/6 inhibitor and locoregional radiotherapy for patients with de novo metastatic breast cancer

The objective of the present study was to assess the outcomes and toxicity of patients treated with concurrent administration of CDK4/6 inhibitors (CDK4/6i) and locoregional radiation therapy (RT), including the breast with a boost or the thoracic wall after mastectomy and the regional lymph node areas. We retrospectively analyzed data from 27 patients with hormone receptor-positive, HER2-negative de novo metastatic breast cancer treated with CDK4/6i and concomitant locoregional RT in 2017/2022. Survival rates were calculated by Kaplan-Meier method. Prognostic factors were tested with log-rank test. CDK4/6i was used as the first systemic metastatic treatment for all the patients, and the median overall treatment time was 26 months. The median time from initiation of CDK4/6i to the start of RT was 10 months (IQR: 7-14 months). The median duration of concomitant CDK4/6i and RT administration was 21 days (IQR: 14.5-23 days). After a median follow-up of 19 months (IQR: 14-36 months), 1 patient died, 11/27 had distant metastases and 1 patient had local recurrence, respectively. The 1- and 3-years progression-free survival (PFS) were 61.4% (95% CI: 45.1%-83.7%) and 53.7% (35.8%-80.5%), respectively. The acute toxicities most observed during RT were neutropenia (44%) and dermatitis (37%). Dermatitis was significantly more frequent in patients with large target volumes (CTV > 911 cc and PTV > 1285 cc). CDK4/6i had to be discontinued in five patients during RT (due to toxicity in three cases and disease progression in two cases). One patient has developed grade 2 late pulmonary fibrosis. Finally, our study demonstrated that concurrent administration of locoregional RT and CDK4/6i did not induce severe late toxicity for most patients.     

Therapy after cyclin-dependent kinase inhibition in metastatic hormone receptor-positive breast cancer: Resistance mechanisms and novel treatment strategies

Endocrine therapy has been the standard of care for patients with metastatic hormone receptor (HR)-positive, HER2-negative breast cancer since the 1970s, improving survival while avoiding the toxicities associated with cytotoxic chemotherapy. However, all HR-positive tumors ultimately develop resistance to endocrine therapy. Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors have more recently become an important component of the management of this breast cancer subtype, significantly delaying time to the disease progression and improving survival when combined with endocrine therapy. However, as with endocrine therapy alone, treatment resistance remains a universal phenomenon. As more women receive CDK4/6 inhibitors as part of their treatment, the management of de novo and acquired resistance to combined CDK4/CDK6 inhibitor plus endocrine therapy regimens has emerged as an important clinical challenge. Several resistance mechanisms have been described, including alterations in the CDK4/6/cyclin D complex or its major effector retinoblastoma protein (pRb), bypass signaling through other cyclin/CDK complexes and activation of upstream signaling pathways, in particular the PI3K/mTOR pathway, but robust biomarkers to predict resistance remain elusive, and the role for continuing CDK4/6 inhibitors after progression remains under investigation. Novel strategies being evaluated in clinical trials include the continuation of CDK4/6 inhibitors through progression, as well as triplet therapy combinations with PI3K inhibitors or immune checkpoint inhibitors.     

CDK4/6抑制剂治疗乳腺癌的研究进展

对于HR+/HER-2-乳腺癌患者来说,内分泌治疗扮演着非常重要的角色.长久以来,医学工作者对于此类患者的内分泌耐药机制以及相关治疗方法的讨论也层出不穷.近年来,CDK4/6抑制剂为HR+患者的带来了福音,CDK4/6抑制剂单药治疗与联合内分泌治疗已经用于晚期乳腺癌的治疗.除了内分泌治疗之外,CDK4/6抑制剂还可以与...     

CDK4/6 Inhibitors as Upfront Treatment in a Patient with Breast Cancer Presenting with a Clinical Critic Situation: A Case Report and Review of the Literature

CDK4/6 inhibitors have revolutionized the treatment algorithm of luminal metastatic breast cancer, becoming the recommended first-line therapy in association with endocrine therapy. However, due to its theoretically greater and more rapid tumor shrinkage, the upfront use of chemotherapy is considered in some clinical situations like visceral crisis. At the state of the art level, a paucity of data is available about the use of CDK4/6 inhibitors in patients presenting with visceral crisis or with life-threatening conditions since this population was historically excluded from clinical trials. In addition, data regarding direct comparison between combinations of chemotherapy and CDK4/6 inhibitors in terms of efficacy, rapidity of responses and long-term outcomes are lacking. We report the case of a 68-year-old woman with luminal metastatic breast cancer presenting at diagnosis with a critical and potentially life-threatening condition. The patient was treated with first-line Abemaciclib plus letrozole and achieved a rapid partial response with sudden clinical stabilization. Although the patient did not technically present with a visceral crisis, this case presentation also endorsed the upfront use of CDK4/6 inhibitor combinations in critical clinical situations in the absence of severe organ dysfunction and after multidisciplinary discussion.     

Ribociclib,a CDK 4/6 inhibitor,plus endocrine therapy in Asian women with advanced breast cancer

The ongoing, Phase Ib MONALEESASIA study is evaluating the efficacy and safety of ribociclib plus endocrine therapy in Asian patients with hormone receptor‐positive, human epidermal growth factor receptor 2‐negative advanced breast cancer. Eligible patients from Japan, Hong Kong, and Singapore were enrolled in this 2‐phase study consisting of a dose‐escalation phase to determine the maximum‐tolerated dose and the recommended Phase II dose of ribociclib plus letrozole, and a dose‐expansion phase to evaluate safety and tolerability of ribociclib plus letrozole, fulvestrant, or tamoxifen. An exploratory biomarker analysis evaluating expression of target genes was also conducted. In the dose‐escalation phase, the maximum‐tolerated/recommended Phase II doses of ribociclib were lower in Japanese patients (300 mg) than in Asian non‐Japanese patients (600 mg). Ribociclib plus endocrine therapy at the recommended Phase II dose had a manageable safety profile, with neutropenia and elevated liver transaminases being the most common adverse events leading to dose modifications or discontinuations, and it demonstrated evidence of clinical activity in both Japanese and Asian non‐Japanese patients. Preliminary efficacy in Asian populations is similar to that observed in White populations studied in previous ribociclib (MONALEESA) trials. Biomarker analysis demonstrated suppression of pharmacodynamic biomarker gene expression, indicating inhibition of target genes by ribociclib combined with endocrine therapy. Results from the ongoing study support the use of ribociclib in combination with letrozole in Asian non‐Japanese patients at the same dose (600 mg) as White patients. In Japanese patients, a lower dose of ribociclib (300 mg) should be considered. Clinicaltrials.gov: NCT02333370.     

HMGB1 is a key factor for tamoxifen resistance and has the potential to predict the efficacy of CDK4/6 inhibitors in breast cancer

Breast cancer is the leading cause of cancer death in women. Hormone-receptor-positive breast cancer (HR + BC) is the most common pathological type of breast cancer, of which the main treatment method is endocrine therapy. Unfortunately, primary or acquired drug resistance greatly limits its efficacy. In recent years, the newly launched CDK4/6 inhibitors could effectively reverse endocrine resistance in breast cancer. However, considering their expensive price and side effects, it is particularly important to find out effective biomarkers and screen sensitive patients. Here, we found through bioinformatics analysis that high mobility group box 1 (HMGB1) expression increased in endocrine-resistant HR + BC. In clinical specimens, the higher expression of HMGB1 was associated with shorter progression-free survival (PFS) for HR + BC patients with endocrine therapy after surgery. For endocrine-resistant breast cancer, compared with HMGB1-negative patients, HMGB1-positive patients who received CDK4/6 inhibitors treatment benefited more in PFS. Moreover, we demonstrated that HMGB1 promoted tamoxifen resistance by combining with the Toll-like receptor 4 (TLR4) and activating nuclear factor kappa B (NF-κB) pathway. CDK4/6 inhibitors could downregulate the expression of HMGB1 and suppress the TLR4-NF-κB pathway, and in turn reverse tamoxifen resistance. These results illuminated the critical role of HMGB1 in the process of tamoxifen resistance, explained the mechanism of CDK4/6 inhibitors reversing tamoxifen resistance, and suggested the feasibility of HMGB1 as a potential biomarker for screening sensitive patients receiving CDK4/6 inhibitors.     

The implementation of CDK 4/6 inhibitors and its impact on treatment choices in HR+/HER2− advanced breast cancer patients: A study of the Dutch SONABRE Registry

In August 2017, cyclin-dependent kinase 4/6 (CDK4/6) inhibitors combined with endocrine therapy have been reimbursed in the Netherlands for patients with hormone receptor positive (HR+), HER2 negative (HER2?) advanced breast cancer (ABC). This study evaluates the implementation of CDK4/6 inhibitors and changes in treatment choices in the Netherlands. All patients diagnosed with HR+/HER2? ABC in 2009 to 2018 in seven hospitals were selected from the Southeast Netherlands Advanced Breast cancer (SONABRE) registry. The 2-year cumulative use of CDK4/6 inhibitors since reimbursement date (August 2017) was assessed using competing-risk methodology in two cohorts. The first cohort included patients with ABC diagnosis between August 2017 and December 2018. The second cohort included patients with ABC diagnosis between 2009 and August 2017, and still alive on August 1, 2017. In addition, treatment choices in the first three lines of therapy in calendar years 2009 to 2018 were evaluated for the total study population. Among patients diagnosed since August 2017 (n = 214), 50% (95% confidence interval [CI] = 43-57) received CDK4/6 inhibitors within 2 years beyond diagnosis. Of eligible patients diagnosed before August 2017 (n = 417), 31% (95% CI = 27-36) received CDK4/6 inhibitors within 2 years following reimbursement. Another 20% of both cohorts are still CDK4/6 inhibitor naïve and on first-line therapy. The use of chemotherapy decreased in first two lines of therapy between 2009 and 2018 (first-line: 29%-13%; second-line: 26%-19%). The implementation rate of CDK4/6 inhibitors since reimbursement is currently 50% within 2 years beyond diagnosis and is expected to increase further. The implementation of targeted therapy decreased the use of chemotherapy as first-line therapy.     

CDK4/6抑制剂在乳腺癌治疗中的研究进展

CDK4/6抑制剂与内分泌治疗的组合策略被越来越多地应用于晚期乳腺癌患者的治疗中.然而,CDK4/6抑制剂不仅仅用于ER阳性、HER2阴性晚期乳腺癌患者的治疗中,其研究应用也扩展到了其他的乳腺癌类型中.本文旨在阐述CDK4/6抑制剂的耐药机制和进展后的后续治疗,以及其在三阴性乳腺癌、HER2阳性乳腺癌、肿瘤免疫和生活质...