UNASSIGNED: Cyclin-dependent protein kinase 4/6 (CDK4/6) is a class of serine/threonine protein kinases that plays a key role in the regulation of the cell cycle. CDK4/6 is highly expressed in cancers such as breast cancer, melanoma, and non-small cell lung cancer (NSCLC). Currently, a variety of CDK4/6 inhibitors have been developed, aiming to develop effective inhibitors to solve CDK4/6 resistance and toxicity.
UNASSIGNED: This article searches patents through Espacenet and reviews the development of widely studied CDK inhibitors and FDA-approved CDK4/6 inhibitors, as well as the latest progress of patented inhibitors with good inhibitory activity against CDK4/6 from 2020 to now.
UNASSIGNED: CDK4/6 is highly expressed in many tumors and has become an important anti-tumor target. Among the patents from 2020 to the present, many inhibitors have good kinase inhibitory effects on CDK4/6 and also show great development potential in anti-tumor. However, there is still an urgent need to develop novel CDK4/6 inhibitors that address challenges such as drug resistance, toxicity, and selectivity.

BACKGROUND: Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) are currently recommended by the National Comprehensive Cancer Network (NCCN) guidelines and the European Society for Medical Oncology (ESMO) guidelines as the first-line (1 L) treatment for patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative, locally advanced/metastatic breast cancer (HR+/HER2- LABC/mBC). Although there are many treatment options, there is no clear standard of care for patients following 1 L CDK4/6i. Understanding the real-world effectiveness of subsequent therapies may help to identify an unmet need in this patient population. This systematic literature review qualitatively synthesized effectiveness and safety outcomes for treatments received in the real-world setting after 1 L CDK4/6i therapy in patients with HR+/ HER2- LABC/mBC.
METHODS: MEDLINE®, Embase, and Cochrane were searched using the Ovid® platform for real-world evidence studies published between 2015 and 2022. Grey literature was searched to identify relevant conference abstracts published from 2019 to 2022. The review was conducted in accordance with PRISMA guidelines (PROSPERO registration: CRD42023383914). Data were qualitatively synthesized and weighted average median real-world progression-free survival (rwPFS) was calculated for NCCN/ESMO-recommended post-1 L CDK4/6i treatment regimens.
RESULTS: Twenty records (9 full-text articles and 11 conference abstracts) encompassing 18 unique studies met the eligibility criteria and reported outcomes for second-line (2 L) treatments after 1 L CDK4/6i; no studies reported disaggregated outcomes in the third-line setting or beyond. Sixteen studies included NCCN/ESMO guideline-recommended treatments with the majority evaluating endocrine-based therapy; five studies on single-agent ET, six studies on mammalian target of rapamycin inhibitors (mTORi) ± ET, and three studies with a mix of ET and/or mTORi. Chemotherapy outcomes were reported in 11 studies. The most assessed outcome was median rwPFS; the weighted average median rwPFS was calculated as 3.9 months (3.3-6.0 months) for single-agent ET, 3.6 months (2.5-4.9 months) for mTORi ± ET, 3.7 months for a mix of ET and/or mTORi (3.0-4.0 months), and 6.1 months (3.7-9.7 months) for chemotherapy. Very few studies reported other effectiveness outcomes and only two studies reported safety outcomes. Most studies had heterogeneity in patient- and disease-related characteristics.
CONCLUSIONS: The real-world effectiveness of current 2 L treatments post-1 L CDK4/6i are suboptimal, highlighting an unmet need for this patient population.

BACKGROUND: The use of Cyclin-Dependent kinase 4 and 6 (CDK4/6) inhibitors has profoundly changed the challenge of endocrine therapy (ET) resistance in hormone receptor-positive (HR+)/HER2-negative (HER2-) breast cancer. However, there is currently no comprehensive evaluation of the evidence for the efficacy of CDK4/6 inhibitors. We conducted an umbrella review to explore the impact of CDK4/6 inhibitor combined with ET on breast cancer by summarizing and assessing the meta-analysis (MA) and systematic review (SR) evidence.
METHODS: Cochrane, PubMed, Embase, and Web of Science databases were searched from inception to August 1st, 2022. Eligible studies were assessed for methodological quality, report quality, and evidence quality using the AMSTAR-2 scale, PRISMA 2020, and GRADE grading systems, respectively. We summarized all efficacy outcomes of CDK4/6 inhibitors for breast cancer and reported them in narrative form.
RESULTS: Our study included 24 MAs and SRs. The strongest evidence demonstrated that CDK4/6 inhibitor combined with ET significantly improved progression-free survival (PFS), overall survival (OS) in advanced breast cancer (ABC). A large body of moderate to high evidence showed a significant association between combination therapy and objective response rate (ORR), and clinical benefit response (CBR) benefit in ABC. Low evidence suggested some degree of benefit from combination therapy in second progression-free survival (PFS2) and time to subsequent chemotherapy (TTC) outcomes in ABC and invasive disease-free survival (IDFS) outcomes in early breast cancer.
CONCLUSIONS: Based on current evidence, CDK4/6 inhibitors combined with ET have great confidence in improving PFS, OS, ORR, and CBR outcomes in patients with ABC, which provides more rational and valid evidence-based medicine for CDK4/6 inhibitor promotion and clinical decision support.

UNASSIGNED: The combination of cyclin-dependent kinase 4/6 (CDK4/6) inhibitors and standard endocrine therapy (ET) in the adjuvant treatment of hormone receptor (HR)-positive/HER2-negative breast cancer (BC) has yielded conflicting results. We performed a pooled analysis of the adjuvant efficacy of CDK4/6 inhibitors by including data from the NATALEE trial, the most recent trial on this topic.
UNASSIGNED: We searched major databases and congress proceedings until 7 June 2023 to identify randomized controlled trials (RCT) comparing adjuvant CDK4/6 inhibitor plus ET combination versus ET in HR-positive/HER2-negative early-stage BC.
UNASSIGNED: Four RCTs involving a total of 17,749 patients were included. According to the pooled analysis of these four studies, significant improvement in invasive disease-free survival (iDFS) was observed with the addition of CDK4/6 inhibitors to standard ET (HzR: 0.81, 95% CI 0.67-0.97). IDFS benefit was irrespective from menopausal status, Ki-67 index, tumor grade, and previous chemotherapy. CDK4/6 inhibitors plus ET had a significant improvement in iDFS in stage 3 whereas there was a trend toward better iDFS in stage 2 (HzR for stage 3: 0.67, 95% CI 0.58-0.78; HzR for stage 2: 0.74, 95% CI 0.55-1.01).
UNASSIGNED: Addition of CDK4/6 inhibitors to standard ET in the adjuvant treatment of HR-positive/HER2-negative early-stage BC improves iDFS.

Combination therapy with cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i: palbociclib, ribociclib, abemaciclib) and endocrine therapy (ET) has been a major advance for the treatment of hormone receptor-positive (HR+), ERBB2 (formerly HER2)-negative (ERBB2-) advanced or metastatic breast cancer.
Randomized phase 3 studies demonstrated that the addition of CDK4/6i reduced the hazard risk of disease progression by approximately half compared with hormonal monotherapy (an aromatase inhibitor, tamoxifen, or fulvestrant) in the first-line (1L) and/or second-line (2L) setting. Hence, the US Food and Drug Administration and European Medicines Agency approved 3 CDK4/6i, in both 1L and 2L settings. However, differences among the CDK4/6i regarding mechanisms of action, adverse effect profiles, and overall survival (OS) are emerging. Both abemaciclib and ribociclib have demonstrated efficacy in high-risk HR+ early breast cancer. While ET with or without CDK4/6i is accepted as standard treatment for persons with advanced HR+ ERBB2- metastatic breast cancer, several key issues remain. First, why are there discordances in OS in the metastatic setting and efficacy differences in the adjuvant setting? Additionally, apart from HR status, there are few biomarkers predictive of response to CDK4/6i plus ET, and these are not used routinely. Despite the clear OS advantage noted in the 1L and 2L metastatic setting with some CDK4/6i, a subset of patients with highly endocrine-sensitive disease do well with ET alone. Therefore, an unanswered question is whether some patients can postpone CDK4/6i until the 2L setting, particularly if financial toxicity is a concern. Finally, given the lack of endocrine responsiveness following progression on some CDK4/6i, strategies to optimally sequence treatment are needed.
Future research should focus on defining the role of each CDK4/6i in HR+ breast cancer and developing a biomarker-directed integration of these agents.

The cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) have become the standard of care for hormone receptor-positive (HR + ) and human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer, improving survival outcomes compared to endocrine therapy alone. Abemaciclib and ribociclib, in combination with endocrine therapy, have demonstrated significant benefits in invasive disease-free survival for high-risk HR+/HER2- early breast cancer patients. Each CDK4/6i-palbociclib, ribociclib, and abemaciclib-exhibits distinct toxicity profiles. Radiation therapy (RT) can be delivered with a palliative or ablative intent, particularly using stereotactic body radiation therapy for oligometastatic or oligoprogressive disease. However, pivotal randomized trials lack information on concomitant CDK4/6i and RT, and existing preclinical and clinical data on the potential combined toxicities are limited and conflicting. As part of a broader effort to establish international consensus recommendations for integrating RT and targeted agents in breast cancer treatment, we conducted a systematic review and meta-analysis to evaluate the safety profile of combining CDK4/6i with palliative and ablative RT in both metastatic and early breast cancer settings.

BACKGROUND: Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have an extremely important impact on the treatment of hormone-sensitive breast cancer (BC) and have radically changed the first-line treatment for metastatic disease with increased rates of treatment response, overall survival (OS), and progression-free survival (PFS). We performed a pooled analysis of randomized trials to validate or refute the hypothesis that there is a significant survival benefit of adding anti-CDK4/6 inhibitors to standard endocrine therapy (ET) in older patients with advanced BC.
METHODS: We selected only English-language phase II/III randomized controlled trials that compared ET alone with ET with anti-CDK4/6 inhibitors in the treatment of advanced BC, with subgroups reporting the outcomes of elderly patients (usually at least 65 years). The primary endpoint was OS.
RESULTS: The review process led to the inclusion of 12 articles and two meeting abstracts, including a total of 10 trials. The addition of CDK4/6 inhibitors to ET (letrozole or fulvestrant) significantly reduced mortality risk by 20% in younger patients (fixed-effect model; HR 0.80; 95% CI 0.72-0.9; p < 0.01) and 21% in older BC patients (HR 0.79; 95% CI 0.69-0.91; p < 0.01). No OS data were available for patients ≥70 years.
CONCLUSIONS: This large, pooled analysis is the first to demonstrate that CDK4/6 inhibitors confer OS and PFS benefits in elderly patients (those aged ≥65 years) with advanced ER + BC and to indicate that it should be discussed with and offered to all patients after geriatric assessment and according to the toxicity profile.

Recent studies have demonstrated that the combination of Cyclin-Dependent Kinase 4/6 Inhibitor (CDK4/6i) and endocrine therapy (ET) is more effective than ET alone and significantly improves progression-free survival (PFS) and overall survival (OS) in patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor-2 negative (HER2-) breast cancer (BC). Palbociclib is the first CDK4/6i approved for use, and its clinical advantages have been shown. However, 30% of patients will continue to develop secondary drug resistance. Therefore, exploring the parameters that can predict the efficacy of Palbociclib and developing a clinical prediction model is essential for evaluating the prognosis of patients.

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) are the preferred regimen for patients with hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced or metastatic breast cancer. However, the optimal treatment sequencing for CDK4/6i with other available therapeutic options is unclear. We conducted a targeted literature review to identify the current evidence on CDK4/6i treatment patterns in patients with breast cancer. The search was initially conducted in October 2021 and subsequently updated in October 2022. Biomedical databases and gray literature were searched, and bibliographies of included reviews were screened for relevant studies. The search identified ten reviews published since 2021 and 87 clinical trials or observational studies published since 2015. The included reviews discussed CDK4/6i usage with or without endocrine therapy (ET) in first-line and second-line treatment for patients with HR+/HER2- advanced or metastatic breast cancer, followed by ET, chemotherapy, or targeted therapy with ET. Clinical studies reported similar treatment sequences consisting of ET, chemotherapy, or targeted therapy with ET prior to CDK4/6i with ET, followed by ET monotherapy, chemotherapy, targeted therapy with ET, or continued CDK4/6i with ET. Current evidence suggests CDK4/6i are effective for HR+/HER2- advanced or metastatic breast cancer in earlier lines of therapy. Efficacy of CDK4/6i as measured by progression-free survival and overall survival was similar within a line of therapy regardless of the type of prior therapy. Survival on different post-CDK4/6i treatments was also similar within the same line of therapy. Additional research is needed to investigate the optimal place in therapy of CDK4/6i and the sequencing of treatments following progression on CDK4/6i.

BACKGROUND: In previous studies on the application of cyclin-dependent kinase 4/6 (CDK4/6) inhibitors combined with endocrine therapy in advanced breast cancer, the outcomes of overall survival (OS) were inconsistent. This systematic review and meta-analysis aimed to further evaluate the clinical efficacy and safety of CDK4/6 inhibitors combined with endocrine therapy on patients with hormone receptor (HR)-positive and human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer.
METHODS: Randomized controlled trials (RCTs) comparing CDK4/6 inhibitors plus endocrine therapy and endocrine therapy alone in patients with HR-positive and HER2-negative advanced breast cancer were searched in the databases of PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure (CNKI), WANFANG and China Science and Technology Journal Database (VIP) up to November 2022. Hazard ratios (HRs) and confidence intervals (CI) of OS, progression-free survival (PFS), the time from randomization to the first recorded disease progression while the patient was receiving next-line therapy or death from any cause (PFS2), time to first subsequent chemotherapy after discontinuation (TTC), and objective response rate (ORR), clinical benefit rate (CBR), safety indicators were extracted. Stata 14.0 software was used for meta analysis and the Cochrane risk-of-bias tool 2.0 was used to evaluate the bias risk.
RESULTS: A total of 9 RCTs with 4,920 participants were included. The addition of CDK4/6 inhibitors to endocrine therapy significantly prolonged OS (HR 0.76; 95% CI: 0.69-0.84; P<0.001), regardless of the application in first-line and second-line treatment, compared with endocrine therapy alone. Similar benefit was observed in PFS (HR 0.56; 95% CI: 0.52-0.60; P<0.001). Moreover, the CDK4/6 inhibitors group improved results of ORR [relative risk (RR) 1.43; 95% CI: 1.27-1.62; P<0.001], CBR (RR 1.24; 95% CI: 1.08-1.41; P<0.01 and RR 1.11; 95% CI: 1.06-1.18; P<0.001), PFS2 (HR 0.68; 95% CI: 0.60-0.76; P<0.001) and TTC (HR 0.65; 95% CI: 0.58-0.72; P<0.001). One of the included RCTs had performance bias. Publication bias was not significant.
CONCLUSIONS: CDK4/6 inhibitors combined with endocrine therapy effectively prolong OS, PFS, PFS2, and TTC, and also improve ORR and CBR in patients with HR-positive, HER2-negative advanced breast cancer, and the safety was within the controllable range.