Primary and acquired endocrine resistance remains a major issue in the treatment of hormone receptor positive breast cancer. Acquired resistance often results from estrogen receptor 1 (ESR1) mutations leading to estrogen independent estrogen receptor activation. Selective estrogen receptor degraders (SERDs) induce degradation of this receptor, thereby overcoming this resistance. The intramuscular administration and modest efficacy of fulvestrant, the first SERD, triggered development of oral, more potent SERDs. This narrative review gives an overview of the current evidence regarding this new drug class.
Medline/PubMed and Embase database were screened using a systematic search strategy. We assessed the San Antonio Breast Cancer Symposium abstract reports, the European Society of Medical Oncology (ESMO) and American Society of Clinical Oncology (ASCO) meeting resources by applying the following terms: ‘SERD’, ‘giredestrant’, ‘elacestrant’, ‘imlunestrant’, ‘amcenestrant’, ‘camizestrant’ and ‘rintodestrant’. ClinicalTrials.gov was consulted to include ongoing trials.
The search retrieved 1191 articles. After screening, 108 articles were retained. In the phase 3 EMERALD trial, elacestrant demonstrated benefit in progression free survival (PFS) in second line metastatic disease in postmenopausal women or men, leading to Food and Drug Administration (FDA) and European Medicines Agency (EMA) approval for the ESR1 mutated population. This PFS advantage was more pronounced among patients who had priorly received at least 12 months of a cyclin-dependent kinases 4/6 inhibitor (CDK4/6i). In the phase 2 SERENA-2 trial, camizestrant improved PFS as second line treatment. However, trials of giredestrant and amcenestrant failed to show PFS benefit in second line metastatic setting. In the preoperative setting, several oral SERDs resulted in a significant reduction of tumoral proliferation. Furthermore, many trials are still in progress.
Oral SERDs constitute an exciting new drug class. Ongoing and future research will further refine the role of these drugs next to standard endocrine treatments and targeted therapies.
With the advancements in conventional treatment modalities such as radiation, chemotherapy, and surgery, as well as the emergence of immunotherapy, the overall cure rate for solid tumor malignancies has experienced a significant increase. However, it is unfortunate that exposure to cancer treatments can have detrimental effects on the function of osteoblasts and osteoclasts, disturbing bone metabolic homeostasis in patients, as well as causing damage to bone marrow cells and other bone tissues. Consequently, certain tumor treatment options may pose a risk for subsequent bone diseases. Common bone disorders associated with cancer treatment include osteonecrosis, bone loss, and secondary bone tumors. (1)Cancer treatment-related osteonecrosis is primarily linked to the use of radiation therapy and certain chemicals, such as bisphosphonates, denosumab, antiangiogenic agents, and immunomodulators. It has been observed that high-dose radiation therapy is more likely to result in osteonecrosis. (2)Chemicals and hormones, particularly sex hormones, glucocorticoids, and thyroid hormones or thyrotropic hormones, are among the factors that can contribute to cancer treatment-related bone loss. (3)Secondary bone tumors differ from metastases originating from primary tumors, and radiotherapy plays a significant role in their development, while chemotherapy may also exert some influence. Radiogenic secondary bone tumors are predominantly malignant, with osteosarcoma being the most common type. Chemotherapy may be a risk factor for the relatively rare occurrence of secondary Ewing sarcoma of the bone. These treatment-related bone disorders have a considerable adverse impact on the prognosis of cancer patients. Hence, it is imperative to prioritize the bone health of patients undergoing cancer treatment and give it further attention.
Recently, cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have emerged as a novel treatment strategy for breast cancer. However, increasing reports of CDK4/6i-associated venous thromboembolism (VTE) have garnered attention. This study assessed CDK4/6i-associated VTE in breast cancer, and examined the effect of CDK4/6i on platelet/coagulation function for the first time in vitro.
PubMed and Embase databases were searched for studies published from the establishment of the database to December 31, 2022 for randomized controlled trials (RCTs) and real-world studies of CDK4/6i in patients with breast cancer, and the data obtained from the included studies were used for meta-analysis. A disproportionality analysis by extracting adverse drug reaction signals of CDK4/6i-associated VTE from the FDA Adverse Event Reporting System (FAERS) database was also conducted. Additionally, the in vitro effect of CDK4/6i on platelet function was assessed based on platelet aggregation tests and flow cytometry, and coagulation function was assessed based on the blood clotting function test.
A total of 16,903 patients in 13 RCTs and 6,490 patients in 9 real-world studies were included in the meta-analysis. In RCTs, VTE occurred in 193 (2.1 %) and 55 (0.7 %) patients in the CDK4/6i and control groups, respectively. In real-world studies, the aggregate incidence rate of VTE was 4.2 % (95 % CI: 2.1, 6.3). The meta-analysis of RCTs revealed that abemaciclib (Odds ratio [OR]: 4.40 [95 % CI: 2.74,7.05], p < 0.001) and palbociclib (OR: 2.35 [95 % CI: 1.34, 4.12], p < 0.01) significantly increased the risk of VTE in patients with breast cancer compared to placebo. FAERS database analysis revealed that abemaciclib (reporting odds ratio [ROR]: 1.63 [95 % CI: 1.36, 1.97]; IC025: 0.67) and ribociclib (ROR: 1.17 [95 % CI: 1.0, 1.39]; IC025: 0.18) demonstrated a significantly increased signal of VTE. Similarly, findings from in vitro experiments demonstrated that abemaciclib enhanced agonist-induced platelet activation, especially when collagen was used as the inducer, and this effect became more prominent with increasing its concentration.
Use of abemaciclib may increase the risk of VTE in patients with breast cancer, which may be partially attributed to the effect of abemaciclib on platelet function. Close monitoring of VTE occurrence is highly recommended while using abemaciclib, especially in patients at a high risk of VTE.