Ribociclib

Ribociclib is an oral anticancer medicine belonging to the cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor class. It is used in combination with endocrine therapy for selected patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer. Ribociclib inhibits CDK4 and CDK6, proteins that help regulate the cell cycle. By reducing phosphorylation of the retinoblastoma protein, it can prevent susceptible cancer cells from progressing from the G1 phase to the S phase of the cell cycle, thereby limiting cell proliferation.

Ribociclib is administered as film-coated tablets taken by mouth. Depending on the clinical setting, it may be combined with an aromatase inhibitor, such as letrozole or anastrozole, or with fulvestrant. In appropriate premenopausal or perimenopausal patients, ovarian function suppression is also required when an aromatase inhibitor is used. Ribociclib has a role in adjuvant treatment of selected patients with early breast cancer at high risk of recurrence and in advanced or metastatic disease. Its use requires assessment of cardiac electrical activity, blood counts, liver function, and potential drug interactions. Dose interruptions or reductions may be necessary when adverse effects occur. Treatment selection and monitoring should be individualized by an oncology team.

Ribociclib was developed as a targeted therapy to inhibit CDK4/6-mediated cell-cycle progression in hormone receptor-positive breast cancer. The US Food and Drug Administration (FDA) first approved it on 13 March 2017 in combination with an aromatase inhibitor for initial endocrine-based treatment of postmenopausal women with HR-positive, HER2-negative advanced or metastatic breast cancer. The European Medicines Agency (EMA) subsequently authorized Kisqali in 2017. The MONALEESA clinical trial programme evaluated ribociclib in advanced breast cancer, including combinations with aromatase inhibitors and fulvestrant. On 17 September 2024, the FDA approved ribociclib with an aromatase inhibitor for adjuvant treatment of adults with HR-positive, HER2-negative stage II and III early breast cancer at high risk of recurrence, based on evidence from the NATALEE trial. Regulatory indications and prescribing requirements vary by jurisdiction. In India, the Central Drugs Standard Control Organisation (CDSCO) has published ribociclib prescribing information and regulatory records; the applicable local product information should be checked before prescribing.

Ribociclib is indicated in combination with endocrine therapy for selected adults with HR-positive, HER2-negative breast cancer. In early breast cancer, it is used with an aromatase inhibitor as adjuvant treatment for eligible patients at high risk of recurrence, following appropriate primary treatment. In advanced or metastatic disease, it may be combined with an aromatase inhibitor as initial endocrine-based therapy or with fulvestrant as initial endocrine-based treatment or after progression on endocrine therapy, according to the applicable label and clinical setting. It is not generally used as monotherapy for these indications. The choice of combination depends on menopausal status, previous endocrine treatment, disease stage, recurrence risk, comorbidities, and local approval criteria. In premenopausal or perimenopausal patients receiving an aromatase inhibitor, ovarian suppression is needed; this may also apply to men receiving an aromatase inhibitor. Treatment should be selected by an oncologist after confirming tumour receptor status and reviewing the patient's treatment history.

Ribociclib is taken orally once daily, with or without food, and tablets should be swallowed whole. For advanced or metastatic breast cancer, the usual adult starting dose in the US prescribing information is 600 mg once daily for 21 consecutive days, followed by 7 days without ribociclib in each 28-day cycle. For adjuvant treatment of eligible early breast cancer, the recommended starting dose is 400 mg once daily for 21 days followed by 7 days off. The accompanying endocrine therapy is administered according to its own prescribing information. Adjuvant treatment may continue for up to three years unless recurrence, unacceptable toxicity, or another clinical reason requires stopping; advanced or metastatic treatment generally continues until disease progression or unacceptable toxicity. Dose interruption or reduction may be needed for low blood counts, liver abnormalities, QT prolongation, or other adverse reactions. Patients should not take an extra tablet after a missed dose or vomiting. Dose adjustments may also be required for severe renal impairment, certain degrees of hepatic impairment, or interacting medicines. Prescribers should follow the locally approved product information, as dosing recommendations can vary by indication and jurisdiction.

Common adverse effects of ribociclib include neutropenia and other decreases in blood-cell counts, nausea, fatigue, diarrhoea, vomiting, headache, constipation, and hair thinning or hair loss. Abnormal liver function tests may occur, and some patients experience infections, reduced appetite, or skin-related symptoms. The frequency and severity of adverse effects depend on the treatment setting, dose, accompanying endocrine therapy, and individual health factors. Many toxicities can be managed with laboratory monitoring, supportive care, temporary treatment interruption, or dose reduction under medical supervision. Patients should report persistent fever, unusual bruising or bleeding, worsening fatigue, yellowing of the skin or eyes, or symptoms suggesting infection. They should not independently change or discontinue treatment without contacting their oncology team, except where emergency care is required.

Important risks associated with ribociclib include severe neutropenia and other bone marrow suppression, hepatotoxicity, and prolongation of the QT interval, which can increase the risk of potentially life-threatening cardiac arrhythmias. Rare but serious complications may include interstitial lung disease or pneumonitis and severe cutaneous adverse reactions. Ribociclib can cause fetal harm and should not be used during pregnancy unless specifically justified under applicable clinical guidance; pregnancy status and reproductive counselling should be addressed before treatment. The medicine is contraindicated in patients with certain serious cardiac conditions or significant baseline QT prolongation, according to the applicable product information. Treatment should be interrupted, reduced, or discontinued when indicated by the severity of toxicity and the prescribing guidelines. Fever, palpitations, fainting, breathing difficulties, extensive rash, or symptoms of liver injury require prompt medical assessment. Baseline and ongoing blood counts, liver function tests, electrolytes, and electrocardiograms are important to identify toxicity early and guide safe treatment decisions.

Before starting ribociclib, clinicians should assess the patient's complete blood count, liver function, serum electrolytes, cardiac history, and baseline electrocardiogram. Potassium, magnesium, calcium, and other relevant abnormalities should be corrected, particularly because ribociclib can prolong the QT interval. Concomitant medicines that prolong QT should generally be avoided, and strong CYP3A inhibitors or inducers require particular attention because they can substantially alter ribociclib exposure. Examples of potentially relevant medicines include certain azole antifungals, macrolide antibiotics, anticonvulsants, and other drugs affecting CYP3A; a pharmacist should review the complete medication list, including supplements and herbal products. Ribociclib may also increase exposure to some CYP3A substrates. Patients with hepatic impairment, significant cardiac disease, electrolyte disturbances, or severe renal impairment require additional assessment and potentially adjusted dosing. Pregnancy, breastfeeding, and fertility considerations should be discussed before treatment. Vaccination plans should be reviewed with the oncology team, with live vaccines generally avoided during significant immunosuppression. Classic enzyme-mediated interactions are clinically important with ribociclib, so medication reconciliation and monitoring should continue throughout therapy.

Confirm HR-positive and HER2-negative tumour status, disease stage, treatment intent, menopausal status, and the intended endocrine partner before prescribing ribociclib. Obtain baseline blood counts, liver function tests, electrolytes, and an ECG, and review cardiac history and all concomitant medicines for QT-prolonging effects and CYP3A interactions. Follow the applicable product information for the timing of repeat ECGs and laboratory tests, particularly during the first treatment cycles and after dose changes. Counsel patients to follow the prescribed 21-days-on, 7-days-off schedule, take tablets consistently, swallow them whole, and avoid doubling a missed or vomited dose. Explain symptoms that require urgent assessment, including fever, palpitations, fainting, jaundice, severe rash, and new or worsening respiratory symptoms. Reinforce adherence to the accompanying endocrine therapy and ovarian suppression where indicated. Check for treatment-related cytopenias, liver abnormalities, and QT prolongation before resuming therapy after an interruption. Pharmacists should verify dose modifications, formulation, adherence, and interaction management at each medication review. Coordination between oncology, pharmacy, nursing, and laboratory services supports timely intervention and safer long-term treatment.