Central nervous system-specific efficacy of CDK4/6 inhibitors in randomized controlled trials for metastatic breast cancer

Recommendations for cyclin‑dependent kinase 4/6 inhibitor treatments in the context of co‑morbidity and drug interactions (Review)

Breast cancer is most frequently diagnosed among women aged 65-74 years and the prevalence of comorbidities in elderly patients with breast cancer is 32.2%. In addition, polypharmacy is quite common in these patients. Understanding the interaction between breast cancer treatment modalities and comorbidities is important, particularly in elderly patients, as comorbidities affect the choice of appropriate treatment and are independent risk factors for survival. A total of three oral cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i), palbociclib, ribociclib and abemaciclib, notably prolonged progression-free survival when combined with endocrine therapy (ET), compared with ET alone in patients with advanced breast cancer (ABC). The present review article therefore addressed the safety, tolerability and toxicity of CDK4/6i treatment in ABC management, compiled real-world data on how multiple clinical and pharmacological features may affect the choice of these drugs and provided practical recommendations for clinical approaches. Before starting treatment with CDK4/6i drugs, all ongoing medical conditions should be inventorized and re-graded, and examination should be performed for any additional disease that the patient may not be aware of. It is also important to obtain a detailed history of concomitant drugs, including prescription and over-the-counter drugs, vitamins, supplements and herbal products. In addition, patients should be advised to consult their oncologist before starting any new medication.

Targeting CDK6 in hormone receptor-positive breast cancer: inhibitor discovery for precision oncology through dynamics study

CDK6 is a critical protein involved in the regulation of the cell cycle, playing an important role in the progression from the G1 to S phase. In breast cancer, dysregulation of this protein is involved in tumour development and progression, particularly in hormone receptor-positive (HR+) breast cancers. The upregulation of CDK6 have been observed in a subset of breast cancers, leading to uncontrolled progression of the cell cycle and increased proliferation of cells. The purpose of this abstract is to provide an outline of CDK6's role. In breast cancer and the therapeutic strategies targeting CDK6 using specific selected inhibitors. To discover viable therapeutic candidates after competitive inhibition of CDK6 with a small molecular drug complex, high throughput screening and docking studies were used. Further, we carried the compounds based on ADMET properties and prediction of activity spectra for substances analysis. Finally, two different compounds were selected to carry out MD simulations. CDK6-IMPHY002642 and CDK6-IMPHY005260 are the two compounds that were identified. Overall, our results suggest that the CDK6-IMPHY002642 and CDK6-IMPHY005260 complex was relatively stable during the simulation. The compounds that have been found can also be further examined as potential therapeutic possibilities. The combined findings suggest that CDK6, together with their genetic changes, can be investigated in therapeutic interventions for precision oncology, leveraging early diagnostics and target-driven therapy.Communicated by Ramaswamy H. Sarma.

New strategies for the treatment of breast cancer with leptomeningeal metastasis

PURPOSE OF REVIEW

Leptomeningeal metastasis is a complication of metastatic breast cancer that has a rising incidence likely due to the increased availability of novel systemic therapies, which have improved survival with better extracranial disease control but with limited intracranial efficacy. A poor prognosis of less than 6 months has historically been associated with leptomeningeal metastasis and it is often an exclusion factor for enrollment in clinical trials. There are limited evidence-based data supporting use of therapeutics in leptomeningeal metastasis patients and recommendations are largely derived from retrospective reports and small prospective studies. However, in recent years, there has been a surge in effective modern therapeutics with promising intracranial activity.

RECENT FINDINGS

The study aims to review the most recent updates in the management of leptomeningeal metastasis in breast cancer. We discuss the effectiveness and limitations of intrathecal administration, predictive biomarkers in the cerebrospinal fluid, proton radiation therapy and promising new systemic therapies such as antibody drug conjugates.

SUMMARY

Ongoing development of clinical trials that allow inclusion of leptomeningeal metastasis are essential for establishing efficacy potential and discovering new treatment options in this population of great unmet need.

TME-targeted approaches of brain metastases and its clinical therapeutic evidence

The tumor microenvironment (TME), which includes both cellular and non-cellular elements, is now recognized as one of the major regulators of the development of primary tumors, the metastasis of which occurs to specific organs, and the response to therapy. Development of immunotherapy and targeted therapies have increased knowledge of cancer-related inflammation Since the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCB) limit immune cells from entering from the periphery, it has long been considered an immunological refuge. Thus, tumor cells that make their way "to the brain were believed to be protected from the body's normal mechanisms of monitoring and eliminating them. In this process, the microenvironment and tumor cells at different stages interact and depend on each other to form the basis of the evolution of tumor brain metastases. This paper focuses on the pathogenesis, microenvironmental changes, and new treatment methods of different types of brain metastases. Through the systematic review and summary from macro to micro, the occurrence and development rules and key driving factors of the disease are revealed, and the clinical precision medicine of brain metastases is comprehensively promoted. Recent research has shed light on the potential of TME-targeted and potential treatments for treating Brain metastases, and we'll use that knowledge to discuss the advantages and disadvantages of these approaches.

Rational design of poly-L-glutamic acid-palbociclib conjugates for pediatric glioma treatment

Brain tumors represent the second most common cause of pediatric cancer death, with malignant gliomas accounting for ∼75% of pediatric deaths. Palbociclib, a selective cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, has shown promise in phase I clinical trials of pediatric patients with progressive/refractory brain tumors using the oral administration route; however, pharmacokinetic limitations and toxicity issues remain. We synthesized a family of well-defined linear and star-shaped polyglutamate (PGA)-palbociclib conjugates using redox-sensitive self-immolative linkers to overcome limitations associated with free palbociclib. Exhaustive characterization of this conjugate family provided evidence for a transition towards the formation of more organized conformational structures upon increased drug loading. We evaluated the activity of conjugates in patient-derived glioblastoma and diffuse intrinsic pontine glioma cells, which display differing reducing environments due to differential glutathione expression levels. We discovered that microenvironmental parameters and the identified conformational changes determined palbociclib release kinetics and therapeutic output; furthermore, we identified a star-shaped PGA-palbociclib conjugate with low drug loading as an optimal therapeutic approach in diffuse intrinsic pontine glioma cells.

Neurologic complications of breast cancer

Breast cancer is a heterogeneous disease with unique neurologic complications that can arise from central nervous system (CNS) involvement or secondary to treatments themselves. As progress is made, with more targeted therapies and combinations available, particularly in the realm of human epidermal growth factor receptor 2 (HER2)-positive disease, the role of these new agents in patients with CNS disease is gradually evolving, although intracranial efficacy itself is lagging. At the same time, both systemic and local standard therapies pose clinical challenges regarding neurologic complications, such as peripheral neuropathy and cognitive changes. The development of new agents, such as immunotherapy, and new strategies, such as incorporating systemic therapies into local therapy, unveil new presentations of neurological complications.

Pyrotinib-based treatments in HER2-positive breast cancer patients with brain metastases

OBJECTIVES

Extensive application of anti-HER2 targeted therapy improves significantly the HER2-positive advanced breast cancer (BC) prognosis, however, it is still difficult to treat brain metastasis. In current study, we explored effective approaches via combining pyrotinib to treat brain metastasis in patients with HER2-positive advanced BC based upon clinical data.

MATERIALS AND METHODS

Current study included 61 HER2-positive BC patients with brain metastases (BM) who were treated by pyrotinib-based regimens. The systemic regimens included pyrotinib combined with capecitabine, pyrotinib combined with nab-paclitaxel, and pyrotinib combined with vinorelbine. Patients' progression-free survival (PFS), overall survival (OS), clinical benefit rate (CBR) and objective response rate (ORR), as well as drug-related adverse events (AEs) in regard of each combination regimen were analyzed.

RESULTS

Pyrotinib-based systemic therapy resulted in 8.6 months median PFS (mPFS) and 18.0 months median OS (mOS) among the BM patients. Regarding different regimens, the combination of pyrotinib with nab-paclitaxel was superior to the combination with capecitabine and vinorelbine with respect to PFS and OS. The central nervous system (CNS) ORR did not showcase significant difference among 3 regimens, however, nab-paclitaxel combined regimen obtained the best peripheral ORR (84.6%) (p ≤ .05).

CONCLUSIONS

Pyrotinib-based combination therapy is safe for HER2-positive brain metastasis treatment. Compared with vinorelbine or capecitabine, pyrotinib combined with nab-paclitaxel is more effective with less toxicity, which is the preferable regimen for HER2-positive brain metastasis.KEY MESSAGESPresent investigation investigated effective methods through combining pyrotinib to treat brain metastasis with HER2-positive advanced brain cancer. The outcomes verified that pyrotinib-based combination therapy was safe and efficient to treat HER2-positive brain metastasis. Therefore, it is effective to treat brain metastasis applying anti-HER2 targeted therapies although pyrotinib showcases efficiency regarding its treatments for the metastasis.

Clinicopathologic and genomic characterizations of brain metastases using a comprehensive genomic panel

Central nervous system (CNS) metastasis is the most common brain tumor type in adults. Compared to their primary tumors, these metastases undergo a variety of genetic changes to be able to survive and thrive in the complex tissue microenvironment of the brain. In clinical settings, the majority of traditional chemotherapies have shown limited efficacy against CNS metastases. However, the discovery of potential driver mutations, and the development of drugs specifically targeting affected signaling pathways, could change the treatment landscape of CNS metastasis. Genetic studies of brain tumors have so far focused mainly on common cancers in western populations. In this study, we performed Next Generation Sequencing (NGS) on 50 pairs of primary tumors, including but not limited to colorectal, breast, renal and thyroid tumors, along with their brain metastatic tumor tissue counterparts, from three different local tertiary centers in Saudi Arabia. We identified potentially clinically relevant mutations in brain metastases that were not detected in corresponding primary tumors, including mutations in the PI3K, CDK, and MAPK pathways. These data highlight the differences between primary cancers and brain metastases and the importance of acquiring and analyzing brain metastatic samples for further clinical management.

A review on the role of cyclin dependent kinases in cancers

The Cyclin-dependent kinase (CDK) class of serine/threonine kinases has crucial roles in the regulation of cell cycle transition and is mainly involved in the pathogenesis of cancers. The expression of CDKs is controlled by a complex regulatory network comprised of genetic and epigenetic mechanisms, which are dysregulated during the progression of cancer. The abnormal activation of CDKs results in uncontrolled cancer cell proliferation and the induction of cancer stem cell characteristics. The levels of CDKs can be utilized to predict the prognosis and treatment response of cancer patients, and further understanding of the function and underlying mechanisms of CDKs in human tumors would pave the way for future cancer therapies that effectively target CDKs. Defects in the regulation of cell cycle and mutations in the genes coding cell-cycle regulatory proteins lead to unrestrained proliferation of cells leading to formation of tumors. A number of treatment modalities have been designed to combat dysregulation of cell cycle through affecting expression or activity of CDKs. However, effective application of these methods in the clinical settings requires recognition of the role of CDKs in the progression of each type of cancer, their partners, their interactions with signaling pathways and the effects of suppression of these kinases on malignant features. Thus, we designed this literature search to summarize these findings at cellular level, as well as in vivo and clinical levels.

A Phase I Dose-Escalation and Dose-Expansion Study of FCN-437c, a Novel CDK4/6 Inhibitor, in Patients with Advanced Solid Tumors

Simple Summary

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have provided clinical benefits for a subset of patients with advanced breast cancer; however, treatment resistance generally emerges over time in patients with breast cancer, and the efficacy of existing CDK4/6 inhibitors in patients with other cancers is modest. The aim of this study was to explore the safety and preliminary antitumor efficacy of a novel, orally available CDK4/6 inhibitor, FCN-437c, in patients with advanced solid tumors. The results demonstrated promising signs of durable tumor response and disease control in this patient population. The safety profile was consistent with that of approved CDK4/6 inhibitors, with no concerning signals in terms of pulmonary, cardiac, or thrombotic risk. The efficacy and safety of FCN-437c merit further study, and this novel agent holds promise as a new alternative treatment for patients with few options.

Abstract

A phase I study evaluated the safety, tolerability, and maximum-tolerated dose (MTD)/recommended phase II dose (RP2D) of FCN-437c, a novel, orally available cyclin-dependent kinase inhibitor (CDK4/6i), in participants with advanced/metastatic solid tumors (aSTs). FCN-437c was escalated from 50 mg (once daily [QD] on days 1–21 of 28-day cycles) to the MTD/RP2D. In the dose-expansion phase, patients with CDK4/6i-treated breast cancer, or KRAS-mutant (KRAS^mut) non-small-cell lung cancer (NSCLC) received the MTD. Twenty-two patients were enrolled. The most common tumors in the dose-escalation phase (n = 15) were breast, colorectal, and lung (each n = 4 [27.3%]). The dose-expansion phase included five (71.4%) patients with breast cancer and two (28.6%) with KRAS^mut NSCLC. Twenty (90.9%) participants experienced FCN-437c–related adverse events. Dose-limiting toxicities occurred in two (33.3%) participants (200-mg dose, dose-escalation phase): grade 3 neutropenia and grade 4 neutrophil count decreased. Due to toxicities reported at 150 mg QD, the MTD was de-escalated to 100 mg QD. One (4.5%) participant (KRAS^mut NSCLC, 100-mg dose) achieved a partial response lasting 724+ days, and five (22.7%) had stable disease lasting 56+ days. In conclusion, FCN-437c was well tolerated with encouraging signs of antitumor activity and disease control. Further exploration of FCN-437c in aSTs is warranted.

Radiotherapy for Leptomeningeal Carcinomatosis in Breast Cancer Patients: A Narrative Review

Simple Summary

Leptomeningeal carcinomatosis (LC) is a rare event in breast cancer (BC) patients that carries an abysmal prognosis. Little progress has been made in this field in the last few decades. Despite innovations in radiotherapy (RT), there is no univocal evidence of its impact on survival. Due to the rarity of the diagnosis, only a few prospective trials have evaluated the role of RT for LC in BC. Nonetheless, most BC patients with LC currently receive RT, depending on local protocols and individual convictions. This review presents the current knowledge on the indications and feasibility of RT for LC in BC, focusing on new technologies and perspectives.

Abstract

Leptomeningeal carcinomatosis (LC), defined as the infiltration of the leptomeninges by cancer cells, is a rare oncological event with the most common etiology being breast cancer (BC), lung cancer, and melanoma. Despite innovations in radiotherapy (RT), firm evidence of its impact on survival is lacking, and concerns are related to its possible neurotoxicity. Owing to a paucity of data, the optimal treatment strategy for LC remains unknown. This review discusses current approaches, indications, and contraindications for various forms of RT for LC in BC. A separate section is dedicated to new RT techniques, such as proton therapy. We also summarize ongoing clinical trials evaluating the role of RT in patients with LC.

Ribociclib plus letrozole in subgroups of special clinical interest with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer: Subgroup analysis of the phase IIIb CompLEEment-1 trial

Background

The phase IIIb CompLEEment-1 study evaluated ribociclib plus letrozole in patients with hormone receptor–positive (HR+), human epidermal growth factor receptor 2–negative (HER2–) advanced breast cancer (ABC). Outcomes were investigated in the following subgroups: central nervous system (CNS) metastases, prior chemotherapy for advanced disease, Eastern Cooperative Oncology Group (ECOG) performance status (PS) 2, and visceral metastases plus prior chemotherapy for advanced disease or ECOG PS 2.

Patients and methods

Patients with HR+, HER2– ABC without prior hormonal treatment for advanced disease received oral ribociclib (600 mg once daily, 3 weeks on/1 week off) plus letrozole (2.5 mg once daily, continuous). Primary endpoint was safety/tolerability, assessed via occurrence of adverse events (AEs); key secondary endpoints included time to progression (TTP), overall response rate, and clinical benefit rate.

Results

51 patients had CNS metastases, 194 received prior chemotherapy for advanced disease, 112 had ECOG PS 2, 146 had visceral metastases plus prior chemotherapy, and 77 had visceral metastases plus ECOG PS 2. Safety results were consistent with those in the overall CompLEEment-1 population; no new safety concerns were identified. The AE profile was manageable with low rates of discontinuations due to AEs. TTP in patients with CNS metastases was consistent with the overall study population and shorter for other patient subgroups. Each patient subgroup achieved meaningful clinical benefit from treatment, consistent with the overall population.

Conclusion

These findings confirm the clinical benefit of ribociclib plus endocrine therapy in high-risk patient subgroups of clinical interest commonly underrepresented in clinical trials.

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CompLEEment-1 evaluated ribociclib plus letrozole in patients with HR+, HER2– ABC.

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Outcomes were evaluated in 5 patient subgroups with traditionally poor prognosis.

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The AE profile was manageable; there were low rates of discontinuations due to AEs.

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Patients in each subgroup achieved meaningful clinical benefit from treatment.

Intracranial Metastatic Disease: Present Challenges, Future Opportunities

Intracranial metastatic disease (IMD) is a prevalent complication of cancer that significantly limits patient survival and quality of life. Over the past half-century, our understanding of the epidemiology and pathogenesis of IMD has improved and enabled the development of surveillance and treatment algorithms based on prognostic factors and tumor biomolecular characteristics. In addition to advances in surgical resection and radiation therapy, the treatment of IMD has evolved to include monoclonal antibodies and small molecule antagonists of tumor-promoting proteins or endogenous immune checkpoint inhibitors. Moreover, improvements in the sensitivity and specificity of imaging as well as the development of new serological assays to detect brain metastases promise to revolutionize IMD diagnosis. In this review, we will explore current treatment principles in patients with IMD, including the emerging role of targeted and immunotherapy in select primary cancers, and discuss potential areas for further investigation.

Mechanisms of Cell Cycle Arrest and Apoptosis in Glioblastoma

Cells of glioblastoma, the most frequent primary malignant brain tumor, are characterized by their rapid growth and infiltration of adjacent healthy brain parenchyma, which reflects their aggressive biological behavior. In order to maintain their excessive proliferation and invasion, glioblastomas exploit the innate biological capacities of the patients suffering from this tumor. The pathways involved in cell cycle regulation and apoptosis are the mechanisms most commonly affected. The following work reviews the regulatory pathways of cell growth in general as well as the dysregulated cell cycle and apoptosis relevant mechanisms observed in glioblastomas. We then describe the molecular targeting of the current established adjuvant therapy and present ongoing trials or completed studies on specific promising therapeutic agents that induce cell cycle arrest and apoptosis of glioblastoma cells.

A Need for More Molecular Profiling in Brain Metastases

As local disease control improves, the public health impact of brain metastases (BrM) continues to grow. Molecular features are frequently different between primary and metastatic tumors as a result of clonal evolution during neoplasm migration, selective pressures imposed by systemic treatments, and differences in the local microenvironment. However, biomarker information in BrM is not routinely obtained despite emerging evidence of its clinical value. We review evidence of discordance in clinically actionable biomarkers between primary tumors, extracranial metastases, and BrM. Although BrM biopsy/resection imposes clinical risks, these risks must be weighed against the potential benefits of assessing biomarkers in BrM. First, new treatment targets unique to a patient's BrM may be identified. Second, as BrM may occur late in a patient's disease course, resistance to initial targeted therapies and/or loss of previously identified biomarkers can occur by the time of occult BrM, rendering initial and other targeted therapies ineffective. Thus, current biomarker data can inform real-time treatment options. Third, biomarker information in BrM may provide useful prognostic information for patients. Appreciating the importance of biomarker analyses in BrM tissue, including how it may identify specific drivers of BrM, is critical for the development of more effective treatment strategies to improve outcomes for this growing patient population.

Advances in the management of breast cancer brain metastases

The development of breast cancer (BC) brain metastases (BrM) is a common complication of advanced disease, occurring in up to half of the patients with advanced disease depending on the subtype. The management of BCBrM requires complex multidisciplinary care including local therapy, surgical resection and/or radiotherapy, palliative care, and carefully selected systemic therapies. Significant progress has been made in the human epidermal growth factor receptor 2-positive (HER2+) BCBrM population due to novel brain penetrable systemic therapies. Increased inclusion of patients with BCBrM in clinical trials using brain-penetrant systemic therapies recently led to the first FDA approval of a HER2-directed therapy specifically in the BCBrM population in the last year. Advances for the treatment of HR+/HER2- and TNBC BCBrM subgroups continue to evolve. In this review, we will discuss the diagnosis and multidisciplinary care of BCBrM. We focus on recent advances in neurosurgery, radiation therapy, and systemic treatment therapies with intracranial activity. We also provide an overview of the current clinical trial landscape for patients with BCBrM.

A common goal to CARE: Cancer Advocates, Researchers, and Clinicians Explore current treatments and clinical trials for breast cancer brain metastases

Breast cancer is the most commonly diagnosed cancer in women worldwide. Approximately one-tenth of all patients with advanced breast cancer develop brain metastases resulting in an overall survival rate of fewer than 2 years. The challenges lie in developing new approaches to treat, monitor, and prevent breast cancer brain metastasis (BCBM). This review will provide an overview of BCBM from the integrated perspective of clinicians, researchers, and patient advocates. We will summarize the current management of BCBM, including diagnosis, treatment, and monitoring. We will highlight ongoing translational research for BCBM, including clinical trials and improved detection methods that can become the mainstay for BCBM treatment if they demonstrate efficacy. We will discuss preclinical BCBM research that focuses on the intrinsic properties of breast cancer cells and the influence of the brain microenvironment. Finally, we will spotlight emerging studies and future research needs to improve survival outcomes and preserve the quality of life for patients with BCBM.

Treatment Patterns and Outcomes of Women with Symptomatic and Asymptomatic Breast Cancer Brain Metastases: A Single-Center Retrospective Study

BACKGROUND

Breast cancer is the most common cancer among women worldwide and the second leading cause of brain metastases (BrM). We assessed the treatment patterns and outcomes of women treated for breast cancer BrM at our institution in the modern era of stereotactic radiosurgery (SRS).

MATERIALS AND METHODS

We conducted a retrospective analysis of women (≥18 years of age) with metastatic breast cancer who were treated with surgery, whole brain radiotherapy (WBRT), or SRS to the brain at the Sunnybrook Odette Cancer Centre, Toronto, Canada, between 2008 and 2018. Patients with a history of other malignancies and those with an uncertain date of diagnosis of BrM were excluded. Descriptive statistics were generated and survival analyses were performed with subgroup analyses by breast cancer subtype.

RESULTS

Among 683 eligible patients, 153 (22.4%) had triple-negative breast cancer, 188 (27.5%) had HER2+, 246 (36.0%) had hormone receptor (HR)+/HER2-, and 61 (13.3%) had breast cancer of an unknown subtype. The majority of patients received first-line WBRT (n = 459, 67.2%) or SRS (n = 126, 18.4%). The median brain-specific progression-free survival and median overall survival (OS) were 4.1 months (interquartile range [IQR] 1.0-9.6 months) and 5.1 months (IQR 2.0-11.7 months) in the overall patent population, respectively. Age >60 years, presence of neurological symptoms at BrM diagnosis, first-line WBRT, and HER2- subtype were independently prognostic for shorter OS.

CONCLUSION

Despite the use of SRS, outcomes among patients with breast cancer BrM remain poor. Strategies for early detection of BrM and central nervous system-active systemic therapies warrant further investigation.

IMPLICATIONS FOR PRACTICE

Although triple-negative breast cancer and HER2+ breast cancer have a predilection for metastasis to the central nervous system (CNS), patients with hormone receptor-positive/HER2- breast cancer represent a high proportion of patients with breast cancer brain metastases (BrM). Hence, clinical trials should include patients with BrM and evaluate CNS-specific activity of novel systemic therapies when feasible, irrespective of breast cancer subtype. In addition, given that symptomatic BrM are associated with shorter survival, this study suggests that screening programs for the early detection and treatment of breast cancer BrM warrant further investigation in an era of minimally toxic stereotactic radiosurgery.

Leptomeningeal Metastases from Solid Tumors: Recent Advances in Diagnosis and Molecular Approaches

Leptomeningeal metastases (LM) from solid tumors represent an unmet need of increasing importance due to an early use of MRI for diagnosis and improvement of outcome of some molecular subgroups following targeted agents and immunotherapy. In this review, we first discussed factors limiting the efficacy of targeted agents in LM, such as the molecular divergence between primary tumors and CNS lesions and CNS barriers at the level of the normal brain, brain tumors and CSF. Further, we reviewed pathogenesis and experimental models and modalities, such as MRI (with RANO and ESO/ESMO criteria), CSF cytology and liquid biopsy, to improve diagnosis and monitoring following therapy. Efficacy and limitations of targeted therapies for LM from EGFR-mutant and ALK-rearranged NSCLC, HER2-positive breast cancer and BRAF-mutated melanomas are reported, including the use of intrathecal administration or modification of traditional cytotoxic compounds. The efficacy of checkpoint inhibitors in LM from non-druggable tumors, in particular triple-negative breast cancer, is discussed. Last, we focused on some recent techniques to improve drug delivery.

The incidence of brain metastases among patients with metastatic breast cancer: a systematic review and meta-analysis

BACKGROUND

Patients with metastatic breast cancer (MBC) are living longer, but the development of brain metastases often limits their survival. We conducted a systematic review and meta-analysis to determine the incidence of brain metastases in this patient population.

METHODS

Articles published from January 2000 to January 2020 were compiled from four databases using search terms related to breast cancer, brain metastasis, and incidence. The overall and per patient-year incidence of brain metastases were extracted from studies including patients with human epidermal growth factor receptor-2 positive (HER2+), triple negative, and hormone receptor (HR)+/hormone receptor negative (HER2-) MBC; pooled overall estimates for incidence were calculated using random effects models.

RESULTS

937 articles were compiled, and 25 were included in the meta-analysis. Incidence of brain metastases in patients with HER2+ MBC, triple negative MBC, and HR+/HER2- MBC was reported in 17, 6, and 4 studies, respectively. The pooled cumulative incidence of brain metastases was 31% for the HER2+ subgroup (median follow-up: 30.7 months, IQR: 24.0-34.0), 32% for the triple negative subgroup (median follow-up: 32.8 months, IQR: 18.5-40.6), and 15% among patients with HR+/HER2- MBC (median follow-up: 33.0 months, IQR: 31.9-36.2). The corresponding incidences per patient-year were 0.13 (95% CI: 0.10-0.16) for the HER2+ subgroup, 0.13 (95%CI: 0.09-0.20) for the triple negative subgroup, and only 0.05 (95%CI: 0.03-0.08) for patients with HR+/HER2- MBC.

CONCLUSION

There is a high incidence of brain metastases among patients with HER2+ and triple negative MBC. The utility of a brain metastases screening program warrants investigation in these populations.

A phase I trial of the CDK 4/6 inhibitor palbociclib in pediatric patients with progressive brain tumors: A Pediatric Brain Tumor Consortium study (PBTC-042)

BACKGROUND

Disruption of cell-cycle regulators is a potential therapeutic target for brain tumors in children and adolescents. The aim of this study was to determine the maximum tolerated dose (MTD) and describe toxicities related to palbociclib, a selective cyclin-dependent kinase 4/6 (CDK4/6) inhibitor in pediatric patients with progressive/refractory brain tumors with intact retinoblastoma protein.

METHODS

Palbociclib was administered orally starting at 50 mg/m² daily for the first 21 days of a 28-day course. Dose escalation was according to the Rolling-6 statistical design in less heavily (stratum I) and heavily pretreated (stratum II) patients, and MTD was determined separately for each group. Pharmacokinetic studies were performed during the first course, and pharmacodynamic studies were conducted to evaluate relationships between drug levels and toxicities.

RESULTS

A total of 21 patients were enrolled on stratum I and 14 patients on stratum II. The MTD for both strata was 75 mg/m² . Palbociclib absorption (mean T_max between 4.9 and 6.6 h) and elimination (mean half-life between 11.3 and 19.5 h) were assessed. The most common toxicity was myelosuppression. Higher palbociclib exposure was associated with grade 3/4 neutropenia and leukopenia. Dose limiting toxicities included grade 4 neutropenia and grade 3 thrombocytopenia and dehydration. No patients had an objective response to palbociclib therapy.

CONCLUSIONS

Palbociclib was safely administered to children and adolescents at a dosage of 75 mg/m² for 21 consecutive days followed by seven days of rest in both strata. Future studies will establish its optimal utilization in pediatric patients with brain tumors.

Molecular Mechanisms of Treatment Resistance in Glioblastoma

Glioblastoma is the most common malignant primary brain tumor in adults and is almost invariably fatal. Despite our growing understanding of the various mechanisms underlying treatment failure, the standard-of-care therapy has not changed over the last two decades, signifying a great unmet need. The challenges of treating glioblastoma are many and include inadequate drug or agent delivery across the blood-brain barrier, abundant intra- and intertumoral heterogeneity, redundant signaling pathways, and an immunosuppressive microenvironment. Here, we review the innate and adaptive molecular mechanisms underlying glioblastoma's treatment resistance, emphasizing the intrinsic challenges therapeutic interventions must overcome-namely, the blood-brain barrier, tumoral heterogeneity, and microenvironment-and the mechanisms of resistance to conventional treatments, targeted therapy, and immunotherapy.

Complete response of leptomeningeal carcinomatosis secondary to breast cancer

Leptomeningeal carcinomatosis (LC) is an unmet medical need associated with death in 4–6 weeks without treatment, delayed by 4 months in some patients with favorable prognosis and aggressive multimodal therapy. Unfortunately, most clinical trials excluded patients with LC, and the best management remains unknown.

Here we present the first report of a LC secondary to HR positive breast cancer with a complete response to CDK4/6 inhibitors abemaciclib, letrozole and hippocampal-avoidance whole-brain radiotherapy.

Management of Brain and Leptomeningeal Metastases from Breast Cancer

The management of breast cancer (BC) has rapidly evolved in the last 20 years. The improvement of systemic therapy allows a remarkable control of extracranial disease. However, brain (BM) and leptomeningeal metastases (LM) are frequent complications of advanced BC and represent a challenging issue for clinicians. Some prognostic scales designed for metastatic BC have been employed to select fit patients for adequate therapy and enrollment in clinical trials. Different systemic drugs, such as targeted therapies with either monoclonal antibodies or small tyrosine kinase molecules, or modified chemotherapeutic agents are under investigation. Major aims are to improve the penetration of active drugs through the blood-brain barrier (BBB) or brain-tumor barrier (BTB), and establish the best sequence and timing of radiotherapy and systemic therapy to avoid neurocognitive impairment. Moreover, pharmacologic prevention is a new concept driven by the efficacy of targeted agents on macrometastases from specific molecular subgroups. This review aims to provide an overview of the clinical and molecular factors involved in the selection of patients for local and/or systemic therapy, as well as the results of clinical trials on advanced BC. Moreover, insight on promising therapeutic options and potential directions of future therapeutic targets against BBB and microenvironment are discussed.

Characterization of the Synergistic Inhibition of IK(erg) and IK(DR) by Ribociclib, a Cyclin-Dependent Kinase 4/6 Inhibitor

Ribociclib (RIB, LE011, Kisqali^®), an orally administered inhibitor of cyclin-dependent kinase-4/6 (CDK-4/6) complex, is clinically effective for the treatment of several malignancies, including advanced breast cancer. However, information regarding the effects of RIB on membrane ion currents is limited. In this study, the addition of RIB to pituitary tumor (GH₃) cells decreased the peak amplitude of erg-mediated K⁺ current (I_K(erg)), which was accompanied by a slowed deactivation rate of the current. The IC₅₀ value for RIB-perturbed inhibition of deactivating I_K(erg) in these cells was 2.7 μM. In continued presence of μM RIB, neither the subsequent addition of 17β-estradiol (30 μM), phorbol 12-myristate 13-acetate (10 μM), or transforming growth factor-β (1 μM) counteracted the inhibition of deactivating I_K(erg). Its presence affected the decrease in the degree of voltage-dependent hysteresis for I_K(erg) elicitation by long-duration triangular ramp voltage commands. The presence of RIB differentially inhibited the peak or sustained component of delayed rectifier K⁺ current (I_K(DR)) with an effective IC₅₀ of 28.7 or 11.4 μM, respectively, while it concentration-dependently decreased the amplitude of M-type K⁺ current with IC₅₀ of 13.3 μM. Upon 10-s long membrane depolarization, RIB elicited a decrease in the I_K(DR) amplitude, which was concomitant with an accelerated inactivation time course. However, the inability of RIB (10 μM) to modify the magnitude of the hyperpolarization-activated cation current was disclosed. The mean current–voltage relationship of I_K(erg) present in HL-1 atrial cardiomyocytes was inhibited in the presence of RIB (10 μM). Collectively, the hyperpolarization-activated cation current was observed. RIB-mediated perturbations in ionic currents presented herein are upstream of its suppressive action on cytosolic CDK-4/6 activities and partly participates in its modulatory effects on the functional activities of pituitary tumor cells (e.g., GH₃ cells) or cardiac myocytes (e.g., HL-1 cells).

Advances in cyclin-dependent kinase inhibitors for the treatment of melanoma

Introduction: Despite the recent advances in the treatment of malignant melanoma with immunotherapy and BRAF/MEK targeted agents, advanced disease still beholds a poor prognosis for a significant proportion of patients. Cyclin-dependent kinase (CDK) inhibitors have been investigated as novel melanoma therapeutics throughout a range of phase 1 and 2 trials, as single agents and in combination with established treatments. Areas covered: This article summarizes the rationale for, and development of CDK inhibitors in melanoma, with their evolution from pan-CDK inhibitors to highly specific agents, throughout clinical trials and finally their potential future use. Expert opinion: Whilst CDK inhibitors have been practice changing in breast cancer management, their efficacy is yet to be proven in melanoma. Combination with BRAF/MEK inhibitors has been hindered by dose-limiting toxicities, but their role may yet to be found within the spectrum of biomarker-derived personalized melanoma management. The effect that CDK inhibitors can have as an adjunct to immunotherapy also remains to be seen.

Evolving treatment strategies of brain metastases from breast cancer: current status and future direction

Remarkable progress in breast cancer treatment has improved patient survival, resulting in an increased incidence of brain metastasis (BM). Current treatment options for BM are limited and are generally used for palliative purposes. Historically, local treatment, consisting of radiotherapy and surgery, is the standard of care due to delivery limitations of systemic treatments through the blood-brain barrier. However, as novel biological mechanisms for tumors and BM have been discovered, several innovative systemic agents, such as small-molecular-targeted therapy and immunotherapy, have begun to change the treatment paradigm. In addition, efforts to maximize antitumor effects have been attempted using combination therapy, informed by tumor biology. In this comprehensive review, we will highlight various clinical trials investigating the treatment of BM in breast cancer patients, discuss presently available treatment options, and suggest potential directions of future therapeutic targets.

Abemaciclib: safety and effectiveness of a unique cyclin-dependent kinase inhibitor

INTRODUCTION

The discovery and the clinical availability of novel cyclin-dependent kinases 4 and 6 inhibitors have profoundly changed the therapeutic scenario of metastatic hormone receptor-positive breast carcinoma. Among these inhibitors, abemaciclib can induce potent and sustained cell cycle arrest and immune system stimulation.

AREAS COVERED

This review summarizes the safety profile and clinical efficacy data on abemaciclib alone or in combination with aromatase inhibitors or fulvestrant in metastatic hormone receptor-positive breast carcinoma. The management of patients treated with abemaciclib is the object of this paper.

EXPERT OPINION

As shown in phase 2 and 3 clinical trials on efficacy and tolerability, abemaciclib is a potentially convenient, safe, and effective agent for the treatment of patients with advanced hormone receptor-positive patients. Orally administered abemaciclib in combination with aromatase inhibitors or fulvestrant has the potential to allow significant improvement in survival outcomes, quality of life, response rate, and duration of response even in poor prognosis subgroups. Adequate patients' information, clinical selection, and prompt, proactive management of side effects are mandatory.