The CNIO Brain Metastasis Group identified a brief period when early brain metastases are unusually vulnerable. In a study published in Cancer Cell in 2025, three medicines destroyed micrometastases in tested models before they became visible, pointing to a potential treatment window before clinical tests can detect the lesions.
Many cancer cells die soon after reaching the brain because the new environment is hostile. Those that survive enter a temporary state researchers call a "proliferative pause": they stop acting aggressively and begin adapting to their surroundings.
Researchers examined the molecular activity of micrometastases that were still too small to detect and found mechanisms that helped the cells survive. When those mechanisms were blocked, the cells could not finish adapting to the brain and died in animal models. Led by Manuel Valiente and the CNIO Brain Metastasis Group, the work contributes to the study of early brain-metastasis seeding as a distinct area of research.
The experiments tested three medicines against molecular targets involved in the process. Two are already approved for other medical uses. All three worked in the tested models, destroying the micrometastases before they became visible metastases.
The project lasted six years. Valiente led the work as head of the CNIO Brain Metastasis Group. More than 70 researchers from around 20 institutions in Spain, the United Kingdom, Germany, France and the United States took part.
The findings appeared in Cancer Cell as part of a peer-reviewed research programme, giving the work a broader basis than a single isolated laboratory result.
Human samples were central to the validation work. The British PEACE consortium supplied samples from tumours and deceased patients, allowing researchers to examine metastases that had been too small to detect clinically.
The CNIO then used living samples from RENACER, the Spanish National Brain Metastasis Network created by Valiente in 2021. The team confirmed the therapeutic effect in those samples.
The same molecular pattern appeared at the advancing edge of established human metastases. Invasive cells spread by attaching themselves to the walls of blood vessels around the metastatic growth. The researchers say medicines that target the vulnerable pause can also restrain these invasive fronts.
For readers following medical developments from Spain, an earlier health report offers a separate example of research and policy affecting treatment access. The CNIO study has a different immediate result: experimental evidence, not a treatment already available to patients.
Manuel Valiente describes the discovery as the beginning of a race to prevent metastasis. Doctors cannot yet identify these micrometastases with available diagnostic tests, and no biomarkers can signal the risk.
The clinical value lies in this hidden interval. Recent neuro-oncology literature says brain metastases are often found only after they become clinically apparent. The earliest period of tumour-cell adaptation may offer the best chance to intervene.
The next steps are to determine which combination of the tested medicines offers the greatest therapeutic benefit and to develop biomarkers for the hidden disease. Clinical trials are the medium- to long-term objective, and the findings still need confirmation in independent patient cohorts.
This research has not produced a preventive treatment for routine care. It has identified a biological window in which metastatic cells can be attacked before symptoms appear, bringing the work closer to preventing brain metastasis and postoperative relapse. A clear gap remains between laboratory evidence and proven patient treatment.
