Ribociclib (Kisqali)
Drug class: CDK4/6 inhibitor
Mechanism of Action
Ribociclib is an orally administered, highly selective small molecule inhibitor of cyclin dependent kinases 4 and 6 (CDK4/6). It is approved in combination with other agents for the treatment of HR positive, HER2 negative advanced or metastatic breast cancer (1).
Inside cells, CDK4/6 act as “ignition switches” for cell division. When bound to Cyclin D, they activate signaling that drives the cell cycle forward. In HR positive breast cancer, hormone signals overstimulate Cyclin D production, keeping CDK4/6 permanently active and forcing uncontrolled cell proliferation (1).
Normally, the retinoblastoma (Rb) protein restrains the transcription factor E2F, preventing premature DNA replication. Active CDK4/6 phosphorylate Rb, releasing E2F and allowing the cell to progress from the G1 phase to the S phase (DNA synthesis) (1).
Ribociclib binds directly to CDK4 and CDK6, blocking their activity. As a result, Rb remains bound to E2F, the cell cycle halts in the G1 phase, and cancer cells are unable to replicate their DNA or divide leading to tumor growth inhibition (1).
Approved Indications
HR+/HER2− advanced or metastatic breast cancer — in combination with an aromatase inhibitor as initial endocrine based therapy, in pre , peri , and postmenopausal women, and in men (1).
HR+/HER2− advanced or metastatic breast cancer — in combination with fulvestrant as initial endocrine based therapy, or after progression on prior endocrine therapy, in postmenopausal women and in men (1).
Adjuvant treatment of HR+/HER2− stage II and III early breast cancer at high risk of recurrence — in combination with an aromatase inhibitor (FDA approval, September 2024) (1,2).
Dosage and Administration
Advanced/Metastatic Breast Cancer: 600 mg (three 200 mg tablets) once daily for 21 consecutive days, followed by 7 days off, in 28‑day cycles. Administered with an aromatase inhibitor or fulvestrant, continued until disease progression or unacceptable toxicity (1).
Early Breast Cancer (Adjuvant): 400 mg (two 200 mg tablets) once daily for 21 consecutive days, followed by 7 days off, in 28‑day cycles. Administered with a non‑steroidal aromatase inhibitor, for up to 3 years or until recurrence or unacceptable toxicity (1).
Key clinical benefits
Survival benefit in advanced disease (3,4,5).
Prolonged progression-free survival (6,7).
Reduced risk of invasive recurrence (8,9).
Key clinical trials
MONALEESA‑2 Trial (First‑line, Postmenopausal, with Letrozole)
The MONALEESA‑2 trial evaluated ribociclib in combination with letrozole as first‑line therapy for postmenopausal women with HR+/HER2− advanced breast cancer. A total of 668 patients with no prior treatment for advanced disease were randomized to receive ribociclib 600 mg (administered three weeks on and one week off) plus letrozole, or placebo plus letrozole. The study demonstrated a significant improvement in median progression‑free survival, reaching 25.3 months compared to 16.0 months in the control arm (HR 0.57; 95% CI 0.46–0.70; P<0.001). At the protocol‑specified final analysis, median overall survival was 63.9 months versus 51.4 months (HR 0.76; 95% CI 0.63–0.93; P=0.004), translating to an approximate 12.5‑month gain and a 24% relative reduction in the risk of death. These results represent one of the longest overall survival outcomes reported in this setting, firmly establishing ribociclib plus letrozole as a standard first‑line option (3,6).
MONALEESA-3 (First/second line, Postmenopausal, with fulvestrant)
The MONALEESA‑3 trial evaluated ribociclib in combination with fulvestrant in postmenopausal women with HR+/HER2− advanced breast cancer, both in the first‑line and second‑line settings. Patients were randomized to receive ribociclib plus fulvestrant or placebo plus fulvestrant. Ribociclib significantly improved overall survival, with a hazard ratio of 0.72 (95% CI 0.57–0.92; P=0.0046), corresponding to an estimated 42‑month survival of 57.8% versus 45.9% in the control arm. Among first‑line patients, median progression‑free survival was 33.6 months compared to 19.2 months. These findings established the benefit of ribociclib with fulvestrant and supported its use after progression on prior endocrine therapy (4).
MONALEESA-7 (Pre/perimenopausal, with endocrine therapy plus goserelin)
The MONALEESA‑7 trial investigated ribociclib in pre‑ and perimenopausal women with HR+/HER2− advanced breast cancer. A total of 672 patients were randomized to receive ribociclib or placebo, added to endocrine therapy (either a non‑steroidal aromatase inhibitor or tamoxifen) plus goserelin. Ribociclib significantly improved median progression‑free survival, achieving 23.8 months compared to 13.0 months in the control arm (HR 0.55; 95% CI 0.44–0.69; P<0.0001). Overall survival was also prolonged, with a hazard ratio of 0.71 (95% CI 0.54–0.95; P=0.00973), marking the first CDK4/6 inhibitor trial to demonstrate a significant survival benefit and the first dedicated to younger, premenopausal patients (5,7).
NATALEE Adjuvant, early breast cancer, with an aromatase inhibitor)
The NATALEE trial assessed ribociclib in the adjuvant setting for early breast cancer. A total of 5,101 patients with HR+/HER2− stage II or III disease were randomized to receive ribociclib 400 mg (three weeks on, one week off) for three years in combination with a non‑steroidal aromatase inhibitor, or the aromatase inhibitor alone. Men and premenopausal women additionally received goserelin. At the final analysis, ribociclib significantly reduced invasive disease events, with a hazard ratio of 0.749 (95% CI 0.628–0.892; P=0.0012). The three‑year invasive disease‑free survival was 90.7% in the ribociclib arm compared to 87.6% in the control arm, confirming its benefit in high‑risk early breast cancer (8,9).
Common Adverse Events
Neutropenia and leukopenia (most common; dose-limiting) (1)
Nausea, vomiting, diarrhoea, constipation (1)
Fatigue and headache (1)
Alopecia (1)
Elevated liver transaminases (ALT/AST) (1)
QTc-interval prolongation (1)
Contraindications/Precautions
Hepatobiliary toxicity (1)
Interstitial lung disease / pneumonitis (1)
Severe cutaneous adverse reactions (1)
Embryo-fetal toxicity (1)
Special notes for the clinician
Hematologic Monitoring: Regular CBC required; neutropenia is the most common adverse event.
Hepatic Safety: Monitor liver function tests; dose adjustments may be needed for elevated transaminases.
Cardiac Considerations: Baseline and periodic ECG recommended; ribociclib can prolong QT interval.
Drug Interactions: Avoid strong CYP3A4 inhibitors/inducers; adjust dose if unavoidable.
Dosing Interruptions: Temporary dose holds or reductions may be required for toxicity management.
Patient Selection: Approved for HR+/HER2− breast cancer in combination with endocrine therapy; efficacy demonstrated across MONALEESA and NATALEE trials.
Special Populations: Use with caution in patients with hepatic impairment; not recommended in severe hepatic dysfunction.
Abbreviations
ABC: advanced breast cancer; AI: aromatase inhibitor; ALT/AST: alanine/aspartate aminotransferase; CBC: complete blood count; CDK: cyclin-dependent kinase; CI: confidence interval; eBC: early breast cancer; ECG: electrocardiogram; HER2: human epidermal gro wth factor receptor 2; HR: hazard ratio; HR+: hormone receptor–positive; iDFS: invasive disease-free survival; LFT: liver function test; LHRH: luteinizing hormone–releasing hormone; mBC: metastatic breast cancer; NSAI: non-steroidal aromatase inhibitor; OS: overall survival; PFS: progression-free survival; QTcF: Fridericia-corrected QT interval; Rb: retinoblastoma protein.
References
Novartis Pharmaceuticals Corporation. KISQALI® (ribociclib) tablets: US prescribing information. East Hanover (NJ): Novartis; 2024. Available at: https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/209935s030lbl.pdf Accessed on 11 September 2026.
US Food and Drug Administration. FDA approves ribociclib (Kisqali) with an aromatase inhibitor for early high-risk breast cancer. September 17, 2024. Available at: https://www.fda.gov/drugs/resources-information-approved-drugs/oncology-cancerhematologic-malignancies-approval-notifications Accessed on 11 September 2026.
Hortobagyi GN, Stemmer SM, Burris HA, et al. Overall survival with ribociclib plus letrozole in advanced breast cancer. N Engl J Med. 2022;386(10):942-950.
Slamon DJ, Neven P, Chia S, et al. Overall survival with ribociclib plus fulvestrant in advanced breast cancer. N Engl J Med. 2020;382(6):514-524.
Im SA, Lu YS, Bardia A, et al. Overall survival with ribociclib plus endocrine therapy in breast cancer. N Engl J Med. 2019;381(4):307-316.
Hortobagyi GN, Stemmer SM, Burris HA, et al. Ribociclib as f irst -line therapy for HR-positive, advanced breast cancer. N Engl J Med. 2016;375(18):1738-1748.
Tripathy D, Im SA, Colleoni M, et al. Ribociclib plus endocrine therapy for premenopausal women with hormone-receptor-positive, advanced breast cancer (MONALEESA-7): a randomised phase 3 trial. Lancet Oncol. 2018;19(7):904-915.
Slamon D, Lipatov O, Nowecki Z, et al. Ribociclib plus endocrine therapy in early breast cancer. N Engl J Med. 2024;390(12):1080-1091.
Hortobagyi GN, Stemmer SM, Saura C, et al. Adjuvant ribociclib plus endocrine therapy versus endocrine therapy alone in HR-positive/HER2-negative early breast cancer: f inal invasive disease-f ree survival results from NATALEE. Ann Oncol. 2025;36(2):149-157.
About the Author
Ms. Mohana Ragavi is an Optometrist and Public Health professional with a specialization in medical writing. Driven by a passion for research and evidence based communication, she has authored and published clinical articles, educational resources, and research papers. Her work reflects a commitment to making complex healthcare information approachable, engaging, and clinically precise, bridging the gap between science and audience understanding.
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