Cyclin-dependent kinase 4/6 inhibitors, which act by inhibiting progression from the G1 to S phases of the cell cycle, include palbociclib, ribociclib, abemaciclib, and trilaciclib. Palbociclib and ribociclib are currently food and drug administration-approved for use in combination with aromatase inhibitors in postmenopausal women with metastatic hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer. Palbociclib is also food and drug administration-approved for use in combination with fulvestrant in hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer progressing after endocrine therapy. Abemaciclib is the newest cyclin-dependent kinase 4/6 inhibitor to gain Food and Drug Administration (FDA) approval, specifically as monotherapy for hormone receptor-positive, human epidermal growth factor receptor 2-negative metastatic breast cancer previously treated with chemotherapy and endocrine therapy. Abemaciclib also shares a similar indication with palbociclib for use in combination with fulvestrant in hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer progressing after endocrine therapy. Trilaciclib use remains largely investigational at this time. However, despite FDA-approval for only metastatic hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer, all four cyclin-dependent kinase 4/6 inhibitors have shown promise in hematologic malignancies and non-breast solid tumors. Although further research is needed, cyclin-dependent kinase 4/6 inhibitors represent intriguing developments in the treatment of various malignancies, including those with such poor prognoses as glioblastoma multiforme, mantle cell lymphoma, and metastatic melanoma. We discuss the approved indications, current research, and areas of future exploration for palbociclib, ribociclib, abemaciclib, and trilaciclib.

Dasatinib is a dual Src/Abl tyrosine kinase inhibitor approved for frontline and second line treatment of chronic phase chronic myelogenous leukemia. Pulmonary arterial hypertension is defined by an increase in mean pulmonary arterial pressure >25 mmHg at rest. Dasatinib-induced pulmonary hypertension has been reported in less than 1% of patients on chronic dasatinib treatment for chronic myelogenous leukemia. The pulmonary arterial hypertension from dasatinib may be categorized as either group 1 (drug-induced) or group 5 based on various mechanisms that may be involved including the pathogenesis of the disease process of chronic myelogenous leukemia. There have been reports of dasatinib-induced pulmonary arterial hypertension being reversible. We report a case of pulmonary arterial hypertension in a 46-year-old female patient with chronic phase chronic myelogenous leukemia on dasatinib treatment for over 10 years. She had significant improvement in symptoms after discontinuation of dasatinib and initiation of vasodilators. Several clinical questions arise once patients experience significant adverse effects as discussed in our case.

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