Who is this trial for?
This trial was for people treated for early breast cancer of the most common type — cancer that is driven by estrogen.
People in the trial had:
- HR-positive, HER2-negative breast cancer (explained below).
- Early-stage disease — stage II or III, including some with no cancer in the lymph nodes but other higher-risk features.
- Already had their main treatment (surgery, and chemo or radiation if needed) and were starting hormone therapy.
What kind of trial is this?
This trial looked at how to prevent the cancer coming back after the main treatment — by adding a medicine to standard hormone therapy.
Background: why researchers asked this question
For HR-positive breast cancer, hormone therapy (pills that block estrogen) after surgery is a cornerstone of treatment and clearly lowers the chance of the cancer returning. But it doesn't remove that risk entirely — and for this type of cancer, a return can happen many years later.
A newer kind of pill, a CDK4/6 inhibitor, was already a standard treatment for this cancer once it had spread. Researchers wanted to know: if you add one of these pills (ribociclib) to hormone therapy earlier, in the after-surgery setting, can you lower the chance of the cancer ever coming back?
The trial: what was tested and how
NATALEE enrolled 5,101 people with HR-positive, HER2-negative early breast cancer across 20 countries. Each person was assigned at random to one of two groups:
- Ribociclib + hormone therapy: the targeted pill for 3 years, plus standard hormone therapy.
- Hormone therapy alone: the current standard.
A lower dose of ribociclib was used than for advanced cancer, to make it easier to tolerate over three years. Researchers measured how many people stayed free of invasive cancer over time (called invasive disease-free survival).
A note before the results
The journey of early breast cancer can be a long and arduous one, particularly for healthy women who really haven't been sick before. Their normal lives get put on hold as they undergo surgery, then chemotherapy, and then radiation. Finally, after all that intense treatment, we prescribe estrogen blockers that they need to take for at least five years. Adding a second pill, for three years, with all its extra blood tests and clinic visits, is a real commitment.
The benefit here is meaningful but modest, and it matters most for people whose cancer carried more risk to begin with. The right answer depends on how much that extra margin is worth to you, and how well you tolerate the medicine.
Results: what they found
After about three years, adding ribociclib lowered the chance of the cancer returning, with a benefit seen across the different groups studied.
Ribociclib + hormone therapy vs hormone therapy alone
About 3 in 100 more people stayed free of invasive cancer with the added pill — a real but modest difference.
Adding ribociclib lowered the risk of the cancer coming back (or a new invasive cancer) by about a quarter.
Low white-blood-cell counts were common but usually manageable. Some people had changes in liver blood tests, so monitoring is needed. The lower dose used here was generally well tolerated.
It is still too early to know whether people simply live longer with the added pill — those results are not yet mature. The benefit so far is measured in fewer cancer returns, not yet in longer life.
The bottom line
For people with stage II or III HR-positive, HER2-negative early breast cancer, adding 3 years of ribociclib to hormone therapy modestly lowered the chance of the cancer coming back. It is now an option for many people in this group, especially those at higher risk of recurrence.
What this could mean for you
- The benefit is real but modest. About 3 in 100 more people stayed cancer-free at 3 years. Whether that's worth three years of an added medicine is a personal decision.
- It takes commitment. Three years of a daily pill means regular blood tests and monitoring for side effects.
- Long-term survival isn't yet known. The trial hasn't yet shown whether it helps people live longer overall.
Who should interpret this
These results describe a study group, not any one person. Your oncology team can weigh your cancer's risk level against the side effects and commitment. A note on the evidence: this trial was funded by the company that makes ribociclib, and people knew which treatment they were getting.
Questions & comments
Have a question about this trial? Ask below. Questions are read and answered by the site. We can't give personal medical advice, but we're glad to explain the research more clearly.