UNASSIGNED: Advanced or metastatic breast cancer (MBC) is associated with poor prognosis and presents many challenges in medical management and treatment decisions. Anticancer drugs that act on cell cycle mechanisms have shown great potential in preclinical studies. In clinical trials, abemaciclib, a reversible ATP-competitive cyclin-dependent kinase 4/6 (CDK4/6) inhibitor developed by Eli Lilly and Company, combined with endocrine therapy (ET) were associated with superior outcomes compared with ET alone in patients with advanced or metastatic hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer, representing a new standard-of-care in this population. Abemaciclib has been approved by the U.S. Food and Drug Administration (FDA) for use in HR+/HER2- MBC. In China, abemaciclib was also approved by the National Medical Products Administration (NMPA) based on findings from the MONARCH plus trial. Recently, abemaciclib have been approved as the first and only CDK4/6 inhibitor by FDA and NMPA for use in HR+/HER2-, node-positive, early breast cancer (EBC) at high risk of recurrence and Ki-67 score ≥20%. Further trials of abemaciclib are ongoing. This is an overview of the clinical development of abemaciclib in breast cancer.
UNASSIGNED: We reviewed English publications in PubMed related to CDK4/6 inhibitors from 2011 to 2021.
UNASSIGNED: In this review, we summarized the mechanism, results of preclinical and clinical studies of abemaciclib, describing current indications for treatment, ongoing clinical trials, safety and tolerability, and future perspectives.
UNASSIGNED: Abemaciclib is a unique CDK4/6 inhibitor with distinctive characteristics and promising data, which bring benefit to HR+, HER2- breast cancer patients.

Estrogen affects cyclin signaling which results in proliferation of breast cancer cells. Breast cancers expressing hormone receptors (known as hormone receptor-positive or HR+ breast cancers) are characterized by dysregulation of cyclin-dependent kinase 4 and 6 (CDK4/6) activity due to overexpression and amplification of genes associated with the cell cycle. Inhibition of CDK4/6, in combination with endocrine therapy (ET), have shown significant clinical efficacy in treating HR+, human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer, leading to global approval of this combination. Abemaciclib is a CDK4/6 inhibitor with higher potency and inhibits a wider range of CDKs compared with other CDK4/6 inhibitors. The MonarchE study is a global, open-label, randomized phase III study of the efficacy of 2-year abemaciclib treatment, together with standard adjuvant ET, in patients who underwent surgery for early-stage HR+, HER2- breast cancer with anatomical or pathological high-risk recurrence features. Preplanned interim analysis of the MonarchE study showed significantly improved invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) with the use of abemaciclib-ET combination therapy in comparison with ET alone. This review focuses on the emerging results and limitations of the MonarchE study in determining the way forward from the CDK4/6-ET combination treatment in HR+, HER2- early-stage breast cancer.

Abemaciclib (ABE) in combination with endocrine therapy represents the mainstay treatment for either endocrine-resistant metastatic or high-risk early-stage HR+/HER2- breast cancer patients. Hence, an adequate knowledge of this agent pharmacodynamic, pharmacokinetic, and of its drug-drug interactions (DDIs) is crucial for an optimal patients management. Additionally, ABE interference with food and complementary/alternative medicines should be taken into account in the clinical practice. Several online tools allow to freely check DDIs and can be easily consulted before prescribing ABE. According to one of this instruments, ABE display the lowest number of interactions among the available cyclin-dependent kinase 4/6 inhibitors. Still, clinicians should be aware that online tools cannot replace the technical datasheet of the drug as well as a comprehensive clinical assessment for each patient. Here we critically review the main pharmacological features of ABE, then focusing on its potential interactions with drugs, food, and alternative medicine, in order to provide a guide for its optimal use in the treatment of HR+/HER2- breast cancer patients.
Pharmacological features and drug interactions of abemaciclib Why was the review done? Abemaciclib, paired with hormone therapy, is a key treatment for breast cancer patients whose cancer cells respond to hormones but not to a protein called HER2. Understanding how this medication functions in the body, how it interacts with other drugs, and how the body processes it is crucial for providing optimal care. What did the authors do? The authors looked for published evidence about the way abemaciclib works into the body and about how it interacts with other drugs (including alternative medicines) or food. Then they summarized these findings. What did the authors find? Abemaciclib absorption, distribution, metabolism and excretion is well known and it is here described. What people eat and any alternative medications they take can affect how abemaciclib works. Online tools are available for doctors to check potential interactions between abemaciclib and other drugs a patient might be using. It’s advisable for doctors to consult abemaciclib data sheet and use online tools before prescribing the drug. Notably, compared to similar treatments, abemaciclib has fewer interactions with other drugs. What does the review mean? This review delves into how abemaciclib works in the body and explore its potential interactions with other drugs, food, and alternative medicines. This information will aid doctors in using abemaciclib effectively for treating breast cancer patients.

Breast cancer is a significant global health concern, contributing to substantial morbidity and mortality among women. Hormone receptor-positive (HR+)/HER2-negative (HER2-) breast cancer constitutes a considerable proportion of cases, and significant advancements have been made in its management. CDK4/6 inhibitors (CDK4/6is) are a new targeted therapy that has demonstrated efficacy in adjuvant, advanced and metastatic settings. The propensity of lobular breast carcinomas for estrogen-rich sites, such as periocular tissues and orbital fat, may explain their tendency for orbital metastases. Current treatment strategies for these cases are predominantly palliative, and the prognosis remains poor. This article presents a unique case of a 51-year-old female with progressive right periorbital edema, pain, and limited ocular motility. An imaging work-up showed bilateral intra and extraconal orbital infiltration, which was biopsied. The histopathologic analysis disclosed mild chronic inflammatory infiltrate with thickened fibrous tissue and moderately differentiated lobular carcinoma cells, positive for GATA3 and CK7 markers, with 100% of tumor nuclei expressing estrogen receptors (ER+). A systemic evaluation showed a multicentric nodular formation in both breasts. Further diagnostic assessments unveiled an HR+/HER2- bilateral lobular breast carcinoma with synchronous bilateral orbital metastases. Systemic treatment was initiated with abemaciclib 150mg twice daily and letrozole 2.5mg once a day. However, this regimen was interrupted due to toxicity. After two weeks, treatment was resumed with a reduced abemaciclib dose (100mg twice daily) alongside letrozole, with a reasonable tolerance. Nearly two years after the initial diagnosis of inoperable metastatic cancer, the patient remains on the same systemic treatment regimen with no signs of invasive disease. This case report is the first of a patient presenting with bilateral orbital metastases from bilateral lobular breast cancer, showing an impressive and sustained response to a first-line treatment regimen combining abemaciclib and letrozole. A literature review on bilateral orbital metastases from breast cancer is also presented.

OBJECTIVE: Cutaneous adverse effects from cyclin-dependent 4 and 6 kinase inhibitors (CDK4/6i) used in metastatic breast cancer are prevalent and well described. Vitiligo-like lesions have been reported and are rare. They can negatively impact patients\' quality of life and may be associated with survival benefits. We describe the clinical characteristics of vitiligo-like lesions in an international cohort of patients treated with CDK4/6i to help improve recognition and management.
METHODS: Retrospective review of patients diagnosed with vitiligo-like lesions from CDK4/6i from five academic institutions in the USA and Europe was performed. Ten patients were included in the study.
RESULTS: Median age of our patients was 55 (range 37-86). Median progression-free survival was 24 months in 5 patients. The median time to rash was 10 months. Sun-exposed areas such as the arms and face were the most affected areas. Multiple skin-directed therapies such as topicals, laser, and phototherapy were trialed with minor success. Mild repigmentation was seen in one patient treated with ruxolitinib cream. CDK4/6 treatment was discontinued due to the vitiligo-like lesions in one patient.
CONCLUSIONS: Clinical characteristics are similar to previously reported findings in case reports and series. We add topical ruxolitinib as a potential treatment option for these patients and include data regarding progression-free survival that should continue to be collected. No definitive conclusions can be made regarding survival benefits from our cohort. Clinicians should refer these patients to dermatologists to aid with management.

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6is) have transformed the treatment of hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer over the last decade. These inhibitors are currently established as first- and second-line systemic treatment choices for both endocrine-sensitive and -resistant breast cancer populations alongside endocrine therapy (ET) or monotherapy. Data on targeted therapy continue to mature, and the number of publications has been constantly rising. Although these drugs have been demonstrated to prolong overall survival (as well as progression-free survival (PFS) in breast cancer patients), changing the paradigm of all current knowledge, they also cause important adverse events (AEs). This review provides the latest summary and update on the safety profile of the three CDK4/6 inhibitors, as it appears from all major phase II and III randomized clinical trials regarding palbociclib, ribociclib, and abemaciclib, including the most relevant 15 clinical trials.

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors and endocrine therapy are the gold standards for systemic therapy for patients with hormone-positive (HR+)/human epidermal growth factor receptor-2-negative (HER2-) metastatic breast cancer. Following progression, no prospective randomized data exist to help guide second-line treatment. Moreover, there is a scarcity of data on rechallenge treatment strategies with another CDK4/6 inhibitor after prior limiting toxicity. We report a real-world experience of rechallenging with abemaciclib after the prior reaction of grade 4 liver toxicity to ribociclib, with high transaminases values of more than 27 times the upper limit of normal (ULN) and unexpected grade 3 neutropenia and diarrhea after a few months of abemaciclib. After two years of treatment, the patient had stable oncological disease, with normal complete blood count, hepatic enzymes, and a very good performance status. We believe that our clinical case, along with others gathered from all around the world, will help with the consolidation of an unmet clinical need to readjust the treatment after experiencing toxicity to CDK4/6 inhibitors.

There is uncertainty regarding the usefulness of CDK4/6-inhibitor-based therapy for hormone receptor positive (HR+), human epidermal grow factor receptor 2 negative (HER2-), metastatic breast cancer (MBC), when CDK4/6 inhibitor treatment had previously failed. Furthermore, a biomarker for abemaciclib resistance has not been identified. Herein, we reported outcomes for an HR+/HER2- MBC patient diagnosed with multiple myeloma and treated with abemaciclib and exemestane, who had cancer progression after treatment with palbociclib and fulvestrant. Thalidomide was used in conjunction with all treatments. The patient had a good response to abemaciclib and exemestane, with progression-free survival much longer than previously reported. PIK3CA and TP53 mutations were identified after cancer progression following abemaciclib treatment. It is unclear whether thalidomide increased the effectiveness of abemaciclib. Whether benefit can be derived by the use of PI3K inhibitors, after cancer progression, requires further investigation, and this may be best accomplished by the use of next-generation sequencing.

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.

Cystic brain metastases (CBM) in patients with breast cancer are rare. They have a worse prognosis than solid brain metastases, and they are less sensitive to radiotherapy. We report a case of hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer with CBM. The patient underwent treatment with docetaxel combined with capecitabine for 5 months, followed by anastrozole maintenance therapy for 10 months, and palbociclib combined with exemestane for 22 months. CBM emerged and bone metastases increased in number. A missense mutation in PIK3CA (exon 10, c.1633G>A [p.Glu545Lys]) was detected by whole-exome next-generation sequencing from peripheral blood samples. After whole-brain radiotherapy (40 Gy/20 fx) combined with 3 months of treatment with everolimus and fulvestrant, CBM demonstrated partial remission (PR), but extracranial bone metastases continued to increase in number. Thus, the patient underwent fourth-line treatment with abemaciclib (100 mg bid) combined with fulvestrant (500 mg). Three months later, CBM significantly demonstrated PR and extracranial bone metastases were stable. At present, the patient has above 9 months of progression-free survival time without obvious adverse effects. This is the first report of abemaciclib combined with fulvestrant in the treatment of CBM in a patient with HR+/HER2- breast cancer.