Abemaciclib

Abemaciclib is an orally administered cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor used in the treatment of selected hormone receptor-positive (HR-positive), human epidermal growth factor receptor 2-negative (HER2-negative) breast cancers. CDK4 and CDK6 are proteins involved in regulating progression of cells through the cell cycle. By inhibiting these kinases, abemaciclib reduces retinoblastoma protein phosphorylation and can limit progression from the G1 phase into the S phase of the cell cycle, thereby slowing the proliferation of cancer cells. Unlike some other CDK4/6 inhibitors, abemaciclib can be administered continuously on a twice-daily oral schedule. It may be used in combination with endocrine therapies such as an aromatase inhibitor, fulvestrant, or tamoxifen, and it also has an approved role as monotherapy in selected patients with advanced or metastatic disease. In high-risk HR-positive, HER2-negative, node-positive early breast cancer, abemaciclib combined with endocrine therapy can be used as adjuvant treatment to reduce the risk of recurrence. Its clinical development has been supported by major phase III programs including MONARCH 2, MONARCH 3, and monarchE.

Abemaciclib was developed as a selective oral inhibitor of CDK4 and CDK6 for hormone receptor-positive breast cancer. The U.S. Food and Drug Administration granted its initial approval in 2017 for certain patients with HR-positive, HER2-negative advanced or metastatic breast cancer. Subsequent FDA approvals expanded its use to combination therapy with endocrine treatment and to adjuvant treatment of adults with HR-positive, HER2-negative, node-positive early breast cancer at high risk of recurrence. The European Commission granted marketing authorization for Verzenios in 2018, with indications covering HR-positive, HER2-negative early and advanced or metastatic breast cancer. In India, CDSCO records document approval and additional indication information for abemaciclib tablets in 50 mg, 100 mg, 150 mg, and 200 mg strengths, including the high-risk early breast cancer indication. The major clinical development programs included MONARCH 1, MONARCH 2, MONARCH 3, and monarchE, which evaluated abemaciclib as monotherapy or in combination with endocrine therapy in different HR-positive, HER2-negative breast cancer settings.

Abemaciclib is indicated in combination with endocrine therapy for the adjuvant treatment of adults with HR-positive, HER2-negative, node-positive early breast cancer at high risk of recurrence. In advanced or metastatic breast cancer, it is used with an aromatase inhibitor as initial endocrine-based therapy and with fulvestrant in patients whose disease has progressed following endocrine therapy. It can also be used as monotherapy in adults with HR-positive, HER2-negative advanced or metastatic breast cancer whose disease has progressed following endocrine therapy and prior chemotherapy in the metastatic setting. For premenopausal or perimenopausal women and for men receiving abemaciclib with an aromatase inhibitor or fulvestrant, ovarian suppression with a gonadotropin-releasing hormone agonist is used according to clinical practice.

Abemaciclib is administered orally and may be taken with or without food. When used in combination with an aromatase inhibitor, fulvestrant, or tamoxifen, the standard starting dose is 150 mg twice daily. When used as monotherapy, the recommended starting dose is 200 mg twice daily. For high-risk early breast cancer, treatment is generally continued for two years, or until disease recurrence or unacceptable toxicity. In advanced or metastatic disease, treatment is generally continued until disease progression or unacceptable toxicity. Dose interruption or reduction may be required for adverse reactions. Tablets should be swallowed whole and should not be chewed, crushed, or split. In patients with severe hepatic impairment, dosing frequency requires adjustment.

Common adverse effects associated with abemaciclib include diarrhea, neutropenia, nausea, abdominal pain, infections, fatigue, anemia, leukopenia, decreased appetite, vomiting, headache, hair loss, and thrombocytopenia. Diarrhea is particularly common and often occurs early during treatment. Laboratory abnormalities involving blood-cell counts and liver enzymes may also occur. The frequency and severity of adverse effects can vary depending on whether abemaciclib is administered alone or with endocrine therapy. Management may include supportive treatment, laboratory monitoring, temporary treatment interruption, or dose reduction according to clinical severity and individual tolerability.

Important risks associated with abemaciclib include severe diarrhea, neutropenia, interstitial lung disease or pneumonitis, hepatotoxicity, venous thromboembolism, and embryo-fetal toxicity. Severe diarrhea may result in dehydration and infection and should be managed promptly with antidiarrheal treatment and adequate fluid intake. Neutropenia can occasionally become severe and has been associated with febrile neutropenia and serious infection. Interstitial lung disease or pneumonitis can be serious or fatal, requiring evaluation of new respiratory symptoms such as cough, dyspnea, or hypoxia. Liver enzyme elevations can require treatment interruption or dose modification. Venous thromboembolic events including deep vein thrombosis and pulmonary embolism have also been reported. Abemaciclib can cause fetal harm and therefore requires appropriate pregnancy precautions.

Patients receiving abemaciclib require monitoring of blood counts and liver function, particularly during the initial months of treatment. Strong CYP3A inhibitors can substantially increase abemaciclib exposure and should generally be avoided or require dose adjustment, while strong and moderate CYP3A inducers can decrease exposure and should generally be avoided. Patients should inform their healthcare provider about prescription medicines, over-the-counter medicines, and supplements before starting treatment. Particular attention should be given to patients with pre-existing hepatic impairment, a history or risk of venous thromboembolism, or respiratory symptoms that could complicate assessment for lung toxicity. Effective contraception should be used during treatment because of potential embryo-fetal toxicity, and breastfeeding is not recommended during treatment.

Before initiating abemaciclib, confirm HR-positive and HER2-negative disease status and assess the clinical setting and indication for treatment. Baseline complete blood counts and liver function tests should be obtained, followed by regular monitoring, particularly during the first four months. Patients should be counselled to begin appropriate antidiarrheal management at the first sign of loose stools, maintain adequate hydration, and promptly report fever or symptoms of infection. New or worsening cough, shortness of breath, chest symptoms, or unexplained hypoxia should be evaluated for possible interstitial lung disease or pneumonitis. Review concomitant medicines carefully for CYP3A interactions and adjust treatment when necessary. For patients receiving combination endocrine therapy, ensure that the appropriate endocrine treatment and ovarian suppression strategy are used according to menopausal status and the prescribed regimen.