Blood biomarker offers window into Alzheimer’s drug response

The emergence of disease-modifying therapies for Alzheimer’s disease has transformed a field that for decades offered little more than symptomatic relief. Yet an important question remains: how can clinicians determine whether these treatments are having the desired biological effect in individual patients without repeatedly subjecting them to costly and resource-intensive brain scans?

Researchers at Korea University College of Medicine believe they may have found part of the answer. Their new study indicates that changes in a blood-based biomarker known as phosphorylated tau 217 (p-tau217) could provide a practical way to monitor patient response to lecanemab, an anti-amyloid therapy approved for early Alzheimer’s disease. The findings add to growing evidence that blood biomarkers may soon play a central role not only in diagnosing neurodegenerative diseases but also in guiding treatment decisions and monitoring therapeutic effectiveness.

A changing landscape for Alzheimer’s care

Alzheimer’s disease affects millions of people worldwide and remains the most common cause of dementia. The pathology is characterised by the accumulation of amyloid-beta plaques and tau protein tangles within the brain, leading to progressive cognitive decline.

Recent years have seen considerable attention focused on anti-amyloid monoclonal antibodies. One of the most significant developments has been the approval of Leqembi, a monoclonal antibody designed to remove amyloid-beta from the brain. Clinical trials have demonstrated that the therapy can modestly slow cognitive decline in people with early-stage Alzheimer’s disease.

However, demonstrating that amyloid is being removed is only part of the picture. Clinicians also need biomarkers that reflect broader disease activity and indicate whether biological changes are translating into improved patient outcomes. This is where p-tau217 has attracted increasing scientific interest.

Tau proteins normally help stabilise neuronal structures. In Alzheimer’s disease, however, tau undergoes abnormal chemical modifications and accumulates into neurofibrillary tangles, one of the hallmark pathological features of the condition. Among the various tau-related biomarkers now being studied, p-tau217 has emerged as one of the most promising. Numerous studies have shown that blood concentrations of p-tau217 correlate strongly with Alzheimer’s pathology and may help distinguish Alzheimer’s disease from other neurodegenerative disorders. Importantly, blood testing offers major practical advantages compared with positron emission tomography (PET) imaging or cerebrospinal fluid sampling. Blood collection is less invasive, cheaper, more widely available and can be repeated frequently.

The Korean researchers therefore sought to determine whether changes in p-tau217 levels could provide insight into how patients respond to lecanemab treatment in routine clinical practice.

Studying treatment response in the real world

The prospective study followed 153 patients receiving lecanemab for early Alzheimer’s disease. Unlike tightly controlled clinical trials, the research reflected real-world treatment conditions, potentially making the findings more relevant to routine healthcare settings. The investigators examined changes in blood p-tau217 concentrations over time and compared these changes with measures of cognitive function. The key observation was the speed with which the biomarker responded.

Within three months of initiating lecanemab therapy, patients showed significant reductions in circulating p-tau217 levels. Such rapid changes suggest that the biomarker is sensitive to biological alterations triggered by anti-amyloid treatment. More importantly, the degree of biomarker reduction appeared to matter. Patients experiencing larger declines in p-tau217 generally demonstrated more favourable cognitive trajectories than individuals showing smaller changes. In particular, greater reductions were associated with slower worsening on the Clinical Dementia Rating Scale-Sum of Boxes (CDR-SB), a widely used measure of cognitive and functional decline in Alzheimer’s disease. These findings provide evidence that biomarker changes may reflect meaningful clinical outcomes rather than merely biochemical fluctuations.

One of the most intriguing aspects of the study was the identification of different response patterns among patients. Researchers observed that participants did not display uniform biomarker trajectories. Instead, distinct patterns of p-tau217 reduction emerged, suggesting variability in biological response to the drug.

This observation reflects an increasingly recognised reality in neurodegenerative medicine: Alzheimer’s disease is not a single, homogeneous disorder. Genetic factors, vascular health, disease stage and underlying biology may all influence how an individual responds to treatment. The study also identified hypertension as a factor associated with a weaker p-tau217 response.

This finding is noteworthy because vascular risk factors have long been linked to cognitive decline and dementia progression. Hypertension can contribute to cerebrovascular damage and may interact with neurodegenerative processes in complex ways. While the study was not designed to establish causal mechanisms, the association highlights the importance of controlling cardiovascular risk factors in patients undergoing Alzheimer’s treatment.

Reducing dependence on brain scans

A major practical implication of the work concerns patient monitoring. Currently, evaluating the biological impact of anti-amyloid therapies often relies on PET imaging. While highly informative, PET scans are expensive, require specialised equipment, and remain inaccessible to many healthcare systems.

Repeated imaging also presents logistical challenges for patients and providers alike.

If future studies confirm the Korean findings, serial blood testing for p-tau217 could offer a more accessible alternative. Clinicians may eventually be able to track treatment response through routine blood sampling rather than repeated imaging sessions. This could significantly expand access to therapy monitoring, particularly in regions where advanced imaging infrastructure is limited. Such an approach would align with broader trends in precision medicine, where minimally invasive biomarkers are increasingly being used to guide treatment decisions and personalise patient care.

Despite the encouraging results, the researchers urge caution. The study provides evidence that p-tau217 may function as a useful pharmacodynamic biomarker, meaning it reflects biological changes resulting from treatment. However, the authors emphasise that larger and longer-term studies are still required before the biomarker can be routinely used to direct clinical management. Several important questions remain unanswered. Researchers must determine how biomarker changes evolve over extended treatment periods, whether specific thresholds predict meaningful clinical benefit, and how p-tau217 should be interpreted alongside other emerging biomarkers. Additional investigation will also be needed to understand why some patients exhibit stronger biomarker responses than others.