A Simple Blood Test Could Transform Breast Cancer Treatment Decisions

How ctDNA Monitoring Works

A New Way to Track Cancer Without Invasive Procedures

For patients with advanced breast cancer, understanding whether a treatment is working can

take time, often requiring scans and waiting weeks or months for visible changes. But what if

doctors could know much sooner, using just a blood test?

Researchers are now exploring a promising tool called circulating tumour DNA (ctDNA),

which consists of tiny fragments of DNA released into the bloodstream by cancer cells. By

analysing these fragments through a method known as a liquid biopsy, scientists can gain

real-time insight into how a cancer is behaving, without the need for repeated tissue biopsies

(1).

Recent findings suggest that this simple blood test could help predict how well patients

respond to treatment, potentially allowing doctors to make faster and more personalized

decisions.

Inside the Study: Tracking Cancer Through Blood

A major clinical study, known as the plasmaMATCH trial, investigated how ctDNA levels

relate to treatment outcomes in patients with advanced breast cancer. The study analysed

blood samples from 167 patients at two key time points: before treatment began and after

approximately four weeks of therapy (2).

Participants were divided into two groups. One group received targeted therapies based on

specific genetic mutations in their tumors, while the other group, patients with triple-negative

breast cancer, received a combination of newer drugs designed to interfere with cancer cell

repair mechanisms (2).

By comparing ctDNA levels with patient outcomes, researchers were able to assess whether

this biomarker could predict treatment success.

Why Starting Levels of ctDNA Matter

One of the study’s key findings was that ctDNA levels before treatment began were strongly

linked to outcomes.

Patients with lower ctDNA levels at the start of treatment tended to respond better and lived

longer without their cancer progressing. This effect was especially noticeable in patients with

triple-negative breast cancer, where those with low ctDNA levels had more than double the

time before their disease worsened compared to those with higher levels. In addition,

treatment response rates differed significantly. Around 40% of patients with low ctDNA

levels responded to therapy, compared to fewer than 10% of those with higher levels (2).

These results suggest that ctDNA may reflect how aggressive a cancer is, helping identify

which patients are more likely to benefit from treatment.

Early Changes Can Reveal If Treatment Is Working

Perhaps even more striking was what researchers discovered after just four weeks of

treatment.

Patients whose ctDNA levels dropped to undetectable levels showed dramatically better

outcomes. In some cases, their cancer remained controlled for nearly a year, compared to

only a few months for patients whose ctDNA remained detectable.

For example:

• In one group, patients with undetectable ctDNA had cancer control lasting about 10.6

months, compared to 3.5 months for others

• In another group, this difference was even larger, 12 months versus 4.3 months

Response rates also improved significantly, with up to 85.7% of patients responding to

treatment when ctDNA became undetectable (2).

These findings highlight ctDNA as a powerful early indicator of whether a therapy is

working, long before traditional scans can confirm it.

Why This Could Change Cancer Care

The implications of this research are significant.

Currently, doctors often need to wait for imaging results to determine whether a treatment is

effective. With ctDNA testing, they may be able to assess this within weeks. This could

allow:

• Faster switching to more effective treatments

• Reduced exposure to ineffective therapies

• More personalized treatment plans tailored to each patient

Because liquid biopsies are minimally invasive, they can also be performed more frequently,

giving clinicians a continuous view of how the disease is evolving (3).

Looking Ahead: From Research to Reality

While these findings are promising, further research is needed before ctDNA testing becomes

a routine part of cancer care. Larger clinical trials are already underway to validate these

results and determine how best to integrate this approach into treatment planning.

If successful, this strategy could represent a major shift toward more responsive and

individualized cancer treatment, where decisions are guided not just by scans, but by real-

time molecular changes in the blood.

Conclusion

A simple blood test measuring circulating tumour DNA has the potential to transform how

advanced breast cancer is treated. By predicting treatment response early and non-invasively, ctDNA could help doctors make faster, more informed decisions, ultimately improving outcomes and quality of life for patients.

References

(1) Nikanjam M, Liu S, Kurzrock R. Liquid biopsy: current technology and clinical

applications. J Hematol Oncol. 2022;15(1):131. doi:10.1186/s13045-022-01351-y

(2) Browne IM, Pascual J, Cutts RJ, Kingston B, Hrebien S, et al. The prognostic and

predictive impact of ctDNA levels in advanced breast cancer. Clin Cancer Res.

2026;32(1):148–158. doi:10.1158/1078-0432.CCR-24-0651

(3) Bartolomucci C, et al. Circulating tumor DNA to monitor treatment response in solid

tumors and advance precision oncology. Front Oncol. 2024;14:11930993.

doi:10.3389/fonc.2024.11930993

Image from: Ignatiadis M, Sledge GW, Jeffrey SS. Liquid biopsy enters the clinic:

implementation issues and future challenges. Nat Rev Clin Oncol. 2021;18(5):297–312.

doi:10.1038/s41571-020-00457-x