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Tucidinostat plus capecitabine shows 25.8% response in advanced HR-positive HER2-negative breast cancerNew Drug Combo Helps Breast Cancer After CDK4/6 Failure

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Key Takeaway
Consider this regimen as a potential option in this population, but note the exploratory and uncontrolled nature of the findings.

This was a phase 2, multicenter trial in 66 patients with HR-positive HER2-negative advanced breast cancer who had previously received CDK4/6 inhibitors. Patients received tucidinostat plus metronomic capecitabine together with either an aromatase inhibitor (Cohort 1) or fulvestrant (Cohort 2). The primary outcome was objective response rate.

The objective response rate was 25.8%, representing 17 partial responses. Median progression-free survival (PFS) for the overall population was 5.39 months (95% CI, 4.07-7.69). In Cohort 1, median PFS was 6.93 months (95% CI, 4.76-12.22), and in Cohort 2, it was 3.98 months (95% CI, 2.79-7.59). Exploratory analyses suggested longer median PFS with wild-type TP53 (7.64 months) versus mutated (3.55 months), and with CTC-negative status (7.59 months) versus CTC-positive (3.78 months).

Safety data showed that 93.9% of patients experienced at least one adverse event; the regimen was reported as well-tolerated. Serious adverse events and discontinuation rates were not reported.

Key limitations include the exploratory nature of the biomarker analyses and the lack of a comparator arm. The median follow-up was 13.88 months. Given the phase 2 design and small sample size, these results are preliminary and should not guide routine practice without further validation.

The Frustrating Reality

Imagine fighting a battle for years. You take the right medicines, you follow the plan, and you feel strong again. Then, the cancer finds a way around your defenses. It grows back. This is what happens for many women with advanced breast cancer.

First, doctors use a group of drugs called CDK4/6 inhibitors. They work well for a while. But eventually, the cancer stops responding. When this happens, options become very limited. Many patients feel like they have nowhere left to turn.

Doctors need new tools for these tough situations. Current choices often do not shrink tumors enough to help patients live longer or feel better. Finding a new way to stop the cancer is urgent. This new approach offers hope where there was little before.

The Surprising Shift

For years, scientists tried adding one drug to another. They tested many combinations. Most did not work as well as hoped. But here is the twist. A new mix of three things works differently. It combines a drug that stops cancer growth signals with a pill that blocks blood vessel formation. Then, it adds standard hormone therapy.

Think of a tumor like a city. It needs roads to get food and oxygen. It also needs specific keys to open its doors and grow.

The first drug, tucidinostat, acts like a wrench. It jams the gears that tell the cancer to grow. The second drug, capecitabine, acts like a roadblock. It stops the new roads from being built. The third part is hormone therapy. It removes the keys the cancer needs to survive.

When you use all three together, the cancer city starves and collapses. It is a multi-pronged attack that is hard for the cancer to ignore.

What The Study Tested

Researchers looked at 66 women with advanced breast cancer. All of them had already taken CDK4/6 inhibitors. Their cancer had grown again.

The women took the new drug mix plus hormone therapy. Some took one type of hormone medicine. Others took a different one, depending on what they had used before. The team watched them closely for over a year. They checked if the tumors got smaller and if the women felt better.

The results were encouraging. About one-quarter of the women saw their tumors shrink significantly. This is called an objective response. For those who responded, the cancer stayed under control for an average of five to seven months.

Not every woman responded. About 25% of patients saw their tumors get smaller. However, the drug combination was safe. Most side effects were mild and manageable. Patients could keep taking their other medicines while on this new plan.

But There Is A Catch

This is where things get interesting. The study found that not everyone benefited equally. Some genetic markers predicted who would do better.

Women whose tumors had a specific mutation called TP53 saw longer control of their cancer. Those without this mutation did not see the same benefit. Also, patients with fewer cancer cells floating in their blood did better than those with many.

This doesn't mean this treatment is available yet.

What Experts Say

The researchers say this combination is a strong option for patients who have no other choices. It fits into the bigger picture of personalized medicine. Doctors will likely use genetic tests to pick the right patients for this therapy. It is not a magic bullet, but it is a useful tool in the toolbox.

If you or a loved one has advanced breast cancer, talk to your doctor about all options. This new combination might be an option in the future. Right now, it is still being studied. It is not approved for general use yet.

Do not stop your current treatment without asking your doctor. Ask if clinical trials are available in your area. These trials give access to new medicines before they are widely used.

Limitations To Keep In Mind

This study had some limits. It only included 66 women. That is a small group. The results might look different in a much larger group of people. Also, the study was done in one region. Results might vary in other places. The cancer cells in different people react differently to drugs.

Scientists will now plan larger studies. They want to confirm these results with more patients. They will also look at how to use genetic tests to find the right patients quickly. If the larger studies succeed, regulators might approve this new combination for use. Until then, it remains a promising option for those in clinical trials.

Study Details

Study typePhase2
EvidenceLevel 3
Follow-up13.9 mo
PublishedApr 2026
View Original Abstract ↓
Treatment options for patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC) that progresses after CDK4/6 inhibitor (CDK4/6i) continue to evolve, and no single regimen has been established as the preferred standard of care. We conducted a phase 2 trial (SYSUCC-020, NCT05411380) to investigate the efficacy and safety of a novel combination of tucidinostat and metronomic capecitabine (mCAP) with endocrine therapy (ET) in patients following progression on CDK4/6i. This trial adopted a Simon two-stage design: eligible patients received tucidinostat plus metronomic capecitabine together with either an aromatase inhibitor (Cohort 1) or fulvestrant (Cohort 2), selected according to prior ET. Seventy-two female patients were screened and sixty-six patients were included in the efficacy and safety analyses. The median follow-up was 13.88 months (Interquartile range, 8.67-20.67) and the objective response rate was 25.8%, with 17 partial responses. The median progression-free survival (PFS) was 5.39 months (95% CI, 4.07-7.69), namely 6.93 months (95% CI, 4.76-12.22) in Cohort 1 and 3.98 months (95% CI, 2.79-7.59) in Cohort 2. Most patients (93.9%) experienced at least one adverse event. In addition, exploratory analyses of biomarkers indicated that the baseline TP53 mutation status (Wild type vs. mutated, 7.64 months vs. 3.55 months) and circulating tumor cell (CTC) status (CTC-negative vs. CTC-positive, 7.59 months vs. 3.78 months) were associated with the median PFS. Our study demonstrated that tucidinostat combined with mCAP and ET is efficacious and well-tolerated in patients with HR-positive HER2-negative ABC previously treated with CDK4/6i.
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