Kisqali (ribociclib) is a cancer medication used to treat hormone receptor-positive, HER2-negative breast cancer, the most common subtype of breast cancer. It is approved for both early-stage breast cancer with a high risk of recurrence and advanced or metastatic breast cancer that has spread beyond the breast. Kisqali works by blocking proteins that drive cancer cell division, and it is always taken alongside hormone therapy rather than on its own.
How Kisqali Works
Before a cell divides, it passes through a series of internal checkpoints. One critical checkpoint determines whether conditions are right for the cell to commit to copying its DNA. Two proteins, CDK4 and CDK6, act as gatekeepers at this step. When they’re activated, they trigger a chain reaction that gives the cell a green light to divide.
In hormone receptor-positive breast cancer, this signaling pathway is often overactive, meaning cancer cells keep getting the green light to multiply. Kisqali blocks CDK4 and CDK6 directly, stalling cancer cells before they can copy their DNA and split into two new cells. This doesn’t kill the cells outright but effectively puts them into a state of arrest, slowing or stopping tumor growth. Two other drugs on the market, palbociclib (Ibrance) and abemaciclib (Verzenio), target the same proteins, but Kisqali is the only one in its class that has demonstrated an overall survival benefit when combined with an aromatase inhibitor as a first-line treatment for postmenopausal women with metastatic disease.
Approved Uses in Breast Cancer
Advanced or Metastatic Breast Cancer
Kisqali’s longest-established use is for breast cancer that has spread to other parts of the body or can’t be removed with surgery. In this setting, it is paired with hormone-blocking therapy. For postmenopausal women, that typically means an aromatase inhibitor such as letrozole or anastrozole. In the MONALEESA-2 trial of 668 postmenopausal patients, adding Kisqali to letrozole produced a 12-month overall survival benefit compared to letrozole alone, with a 24% reduction in the risk of death.
For premenopausal and perimenopausal women, Kisqali is combined with an aromatase inhibitor plus a medication that suppresses ovarian hormone production (goserelin), since aromatase inhibitors alone don’t fully block estrogen in women who are still menstruating. The National Cancer Institute has described this combination as a standard treatment option for hormone receptor-positive, HER2-negative metastatic disease that isn’t immediately life-threatening.
Early-Stage Breast Cancer
Kisqali is also approved for early breast cancer that has a high risk of coming back after surgery. In this adjuvant setting, the goal is not to shrink an existing tumor but to reduce the chance of recurrence. It is taken alongside an aromatase inhibitor, and the dose is lower than what’s used for metastatic disease: 400 mg daily compared to 600 mg.
How Kisqali Is Taken
Kisqali comes as a tablet taken once a day, preferably in the morning, with or without food. The schedule follows a 28-day cycle: 21 days on the medication followed by 7 days off. This on-off pattern gives the body time to recover from side effects, particularly drops in white blood cell counts, before the next cycle begins.
Tablets should be swallowed whole. If you vomit after taking a dose or miss one entirely, you skip it and take the next dose at the usual time the following day. No doubling up.
Common Side Effects
The most frequently reported side effects, each occurring in more than 20% of patients, include low white blood cell counts (neutropenia and leukopenia), nausea, infections, fatigue, diarrhea, vomiting, hair thinning, headache, constipation, rash, and cough. Neutropenia is the most common and the reason for the week-off schedule and regular blood monitoring.
Kisqali can also affect heart rhythm by prolonging a specific electrical interval in the heartbeat called QTc. This doesn’t cause symptoms in most people, but in rare cases it can lead to dangerous heart rhythm changes. Because of this, you’ll have blood tests and heart rhythm monitoring (ECGs) before starting treatment, around day 14 of the first cycle, and at the beginning of the second cycle. Blood work continues every two weeks for the first two cycles, then at the start of each cycle after that. Electrolyte levels, particularly potassium and magnesium, are checked at the beginning of each cycle for the first six cycles since low levels can worsen heart rhythm issues.
Who Kisqali Is Not For
Kisqali targets a specific subtype of breast cancer: hormone receptor-positive, HER2-negative. It has no role in treating triple-negative breast cancer or HER2-positive breast cancer, which are driven by different biological pathways. It is also not used as a standalone treatment. Its mechanism of blocking CDK4/6 complements hormone therapy, so the two are always prescribed together.