What Is Ibrance, and Why Does It Matter?
Ibrance (palbociclib) is a targeted cancer pill for treating certain forms of breast cancer. The FDA has now approved its use combined with other targeted anti-human epidermal growth factor receptor 2 (HER2) therapies (trastuzumab, with or without pertuzumab) plus hormone (endocrine) therapy as an ongoing or “maintenance” option for adults with hormone receptor-positive (HR+) and HER2-positive (HER2+) breast cancer that is locally advanced or has spread (metastatic) after being brought under control with initial treatment.
About 10% of breast cancers are both HR+ and HER2+, also known as double-positive or triple-positive breast cancer. Resistance to combined anti-HER2 and hormone therapy, even after promising initial results, is one of the key challenges faced by many patients with HR+, HER2+ metastatic breast cancer. So having another option for maintenance therapy may be important for many affected individuals.
First approved in 2015, Ibrance is a pill that targets enzymes called cyclin-dependent kinases (CDK4 and CDK6) that promote growth and survival of cancer cells. By blocking them, Ibrance can slow cancer cell growth. The manufacturer reports that Ibrance is the first CDK4/6 inhibitor approved for HR+ metastatic breast cancer irrespective of HER2 status.
Trastuzumab and pertuzumab target the HER2 protein on cancer cells and help slow cancer growth. Trastuzumab may also make it easier for the immune system to attack the cancer cells. Adding hormone therapies lowers the levels of hormones, such as estrogen, or blocks their effects on cancer cells, helping slow or stop the growth of HR+ breast cancers.
This approval matters as it provides another way of combining a CDK4/6 inhibitor with standard anti‑HER2 and hormone therapies, helping keep patients’ cancer from progressing. It also offers another treatment option that can be used across a broader group of patients with HR+ metastatic breast cancer irrespective of HER2 status.
Why Was It Approved?
The FDA’s decision was based on data from a clinical study involving 518 adults with HR+, HER2+ metastatic or locally advanced breast cancer who did not show any evidence of cancer growth after an initial induction treatment with a taxane and trastuzumab, with or without pertuzumab. Following induction therapy, the patients were randomly assigned to take either Ibrance plus anti-HER2 therapy (trastuzumab or trastuzumab plus pertuzumab) and hormone therapy or only anti‑HER2 and hormone therapy without Ibrance. Treatment continued until the cancer worsened or side effects required stopping the therapy.
In the study, combining Ibrance with anti‑HER2 and hormone therapy led to a significantly longer time before the cancer spread again or worsened, compared to anti‑HER2 and hormone therapy alone. This improvement was statistically significant. The study also reported a 24% lower risk for cancer progression or death by adding Ibrance to anti‑HER2 and hormone therapy. The median time without cancer growth could not be estimated at the time of analysis because many results were still pending, and overall survival data were not yet completed. Ibrance’s safety and tolerability were in line with its known safety profile.
The most common side effects include low white blood cell, neutrophil, red blood cell, and platelet counts; nausea; diarrhea; infections; mouth sores; higher liver enzyme levels; low calcium or potassium levels; fatigue; weakness; headache; rash or itching; muscle spasms; and increases in creatinine or alkaline phosphatase levels. Important warnings include very low white cell counts (neutropenia) that may cause serious or life-threatening infections, lung inflammation (interstitial lung disease or pneumonitis), and harm to a fetus.
What Do I Need to Know?
Ibrance is available as tablets or capsules. The prescribed dose is taken by mouth once daily for 21 days in a row, followed by 7 days off, for a 28‑day cycle. You may take it with or without food at about the same time every day. Swallow tablets or capsules whole; do not chew, crush, open, or split them. If you vomit or miss a dose, do not take an extra tablet that day. Take your next dose at the regular time. Do not eat grapefruit or drink grapefruit juice while on this medicine.
Before starting Ibrance, tell your health care provider about all of your medical conditions and if you have an active infection or liver or kidney problems. If you are pre‑ or perimenopausal and your care team selects Ibrance, you should also receive another medicine called a luteinizing hormone‑releasing hormone agonist.
Inform your health care provider about all prescription and nonprescription medicines, vitamins, and herbal products you take to help avoid serious interactions. Avoid medicines that strongly inhibit or induce CYP3A enzymes as they can significantly affect how the medicine is broken down in the body. If a strong CYP3A inhibitor cannot be avoided, your health care provider may lower your Ibrance dose.
Let your health care provider know if you are pregnant or planning to get pregnant as Ibrance can harm a fetus. Use effective birth control during treatment and for three weeks after the last dose. Avoid breastfeed during treatment and for three weeks after the final dose. Ibrance may affect fertility in men and has the potential to damage genetic material (genotoxicity). Your health care provider may advise you to consider preserving sperm before starting treatment with Ibrance and your female partners to use effective birth control during the treatment and for three months after the last dose.
Your health care provider will check your blood counts before you start treatment, at the beginning of each cycle, and on day 15 of the first two cycles. Call your health care provider right away if you notice any signs or symptoms of infection such as fever and chills because low white cell counts can lead to serious infections. Contact health care services if you notice any new or worsening symptoms related to your lungs such as chest pain, cough with or without mucus, trouble breathing, or shortness of breath.