CNIO researchers have identified a vulnerable stage in early brain metastases. Three drugs eliminated microscopic lesions in mice and human tissue before they became clinically detectable, opening a possible route to preventing recurrence.
Three drugs cleared microscopic brain metastases in laboratory models before clinical scans could detect them. The CNIO-led study found a short biological weakness that appears as tumour cells adapt to the brain. Published in Cancer Cell on 28 September 2026, the research points to a possible way to stop metastases before symptoms appear.
The vulnerable period starts after tumour cells travel from cancers such as those of the lung, breast or skin. Many do not survive in the brain. The cells that remain enter what researchers call a "proliferative pause". Their growth slows for a time, while molecular systems help them adjust to the new environment. Reports from MedicalXpress and other outlets describe this pause as a possible treatment window, not an established option for patients.
That pause is the target.
Two of the three drugs tested in the study are already approved for other medical indications. Their activity against early brain micrometastases was demonstrated in mouse models and assessed using human tumour material.
The CNIO team tested three drugs against molecules involved in that adjustment process. Micrometastases disappeared in mouse models. Manuel Valiente and Pedro García-Gómez led the work. It took more than six years and involved over 70 scientists from about 20 institutions in Spain, the United Kingdom, Germany, France and the United States.
The most dangerous stage may also be the hardest to see. RTVE and other Spanish outlets reported that the strategy is aimed at microscopic disease before it forms a metastasis that doctors can see on a scan. It is not designed to replace treatment for an established lesion.
Researchers first mapped molecular activity in early lesions that are too small for routine clinical detection. They then compared the mouse results with human tissue. PEACE provided some of the most useful material. The British repository contains tumour samples collected during autopsies. Those samples revealed micrometastases that had not been found during the patients' lives.
The evidence held up in human samples.
The study points to BCL2 inhibition as one possible way to interfere with the early adaptation of tumour cells in the brain. The implication is preventive: the aim would be to stop hidden micrometastases from progressing, not to replace treatment for an already visible brain metastasis.
After confirming the same mechanisms in the PEACE samples, the investigators turned to RENACER. Manuel Valiente created the Spanish consortium in 2021. Human brain-metastasis tissue collected during neurosurgery supported the effects seen in the experimental models. Mariam Jamal-Hanjani of the UCL Cancer Institute and principal investigator of PEACE said the findings could support new efforts to stop microscopic disease from progressing with targeted treatment.
Detection remains the immediate clinical problem. No diagnostic test can currently find these micrometastases at their earliest stage. There are also no biomarkers that show which patients carry them. A treatment for invisible disease therefore cannot yet be used as a routine preventive intervention.
The findings may also matter after surgery. Established brain metastases can send out invasive fronts by attaching to blood-vessel walls around the tumour. In human metastasis samples, the CNIO team found that the drugs used against the proliferative pause also slowed these fronts. That creates a research path towards lowering the risk of recurrence after an operation. The result builds on earlier research on the same hidden stage of the disease.
Valiente's group is now testing which combination of the three drugs brings the greatest therapeutic benefit. The researchers are also looking for biomarkers that could reveal lesions beyond the reach of current imaging. The longer-term goal is to reach clinical trials and test whether treatment can stop brain metastases from becoming clinically relevant. MedicalXpress and other reports stress that the evidence is still preclinical, even though the study used mouse models and human samples.
The collaboration includes the Centro Nacional de Análisis Genómico, the Instituto de Neurociencias CSIC-UMH, the Universidad de Cantabria, the Francis Crick Institute, University College London, the University of Oxford, the Universidad de Castilla-La Mancha, the NCI and UT Southwestern Medical Center, along with PEACE and RENACER. The evidence is not yet a treatment for patients. It points prevention research towards the short adaptation phase before a tumour becomes visible. Biomarkers and clinical testing will determine whether that idea can move forward.
