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AstraZeneca’s experimental pill, camizestrant, has demonstrated a significant breakthrough in the fight against advanced breast cancer, according to new clinical trial results unveiled at the American Society of Clinical Oncology (ASCO) annual meeting in Chicago. The study found that using a blood test to guide early intervention with camizestrant at the first signs of resistance to standard treatments reduced the risk of disease progression or death by 56% in women with hormone receptor-positive, HER2-negative breast cancer—the most common subtype of the disease.
How the Study Worked
For the first time, researchers employed a liquid biopsy—a blood test that detects tumor DNA—to identify when patients began developing resistance to conventional endocrine therapies, even before tumors were visible on imaging scans. This approach allowed doctors to switch treatments sooner, aiming to “stay ahead of the curve” and intervene before the disease could advance.
The international SERENA-6 Phase III trial enrolled 3,256 patients across 23 countries. Participants who switched early to camizestrant, combined with widely used CDK4/6 inhibitors, saw their cancer stabilize for a median of 16 months, compared to about nine months for those who continued on standard therapies.
Expert Reactions
Dr. Eleonora Teplinsky, a breast cancer specialist at Valley-Mount Sinai Comprehensive Cancer Care and an ASCO expert, emphasized the significance of early intervention:
“When patients progress on scans, we’re already behind. An early switch approach, before disease progression, allows doctors to essentially stay ahead of the curve,” she said.
Dr. Catherine Elliott, director of research at Cancer Research UK, hailed the findings as a “clear example of how blood tests are starting to transform cancer treatment,” noting that tracking tumor DNA in blood can help spot resistance and optimize therapy before cancer has a chance to grow.
Implications for Future Treatment
The results are being described as potentially “transformational,” marking the first pivotal trial to show the clinical value of monitoring circulating tumor DNA to detect and treat emerging resistance in first-line breast cancer therapy. Camizestrant is the first next-generation oral SERD (selective estrogen receptor degrader) and complete estrogen receptor antagonist to demonstrate consistent benefits in this setting.
While camizestrant is not yet approved by the U.S. Food and Drug Administration, experts believe these findings could pave the way for a new standard of care in managing advanced hormone receptor-positive, HER2-negative breast cancer.
Side Effects and Next Steps
The trial reported that only 1% of patients discontinued camizestrant due to side effects, suggesting the drug is generally well tolerated2. Further results and long-term follow-up data are expected as research continues.
Disclaimer:
This article is based on early-stage clinical trial results and expert commentary presented at the 2025 ASCO annual meeting. Camizestrant is not yet approved by regulatory authorities for general use. Patients should consult their healthcare providers before making any changes to their treatment plans. The findings discussed here may not apply to all individuals and further research is ongoing to confirm the benefits and safety of this approach.
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