Biological changes in the blood can reveal signs of certain types of cancer several years before the disease is diagnosed. In a new study, researchers were able to identify patterns associated with prostate cancer up to eight years prior to clinical diagnosis. Breast cancer also left early traces, but the results there were significantly weaker.

Researchers at the University of Oxford and the University of Toronto analyzed stored blood samples from individuals who were cancer-free when the samples were taken. The researchers were then able to retrospectively compare samples from participants who later developed cancer to samples from people who remained cancer-free.

Instead of only searching for DNA that had been released by an already existing tumor, the researchers examined so-called DNA methylation—chemical changes that affect how genes are turned on and off.

According to Oxford, such changes could be detected long before some of the participants received their cancer diagnoses.

Most Clear for Prostate Cancer

The strongest results were seen for prostate cancer.

The researchers found specific methylation patterns in the blood of people who would be diagnosed with the disease several years later. These patterns made it possible to distinguish them from people who did not develop prostate cancer.

In some cases, the signals could be identified between five and eight years before diagnosis, according to Oxford.

This does not mean that the blood test could show that a person already had a tumor. Rather, it seems to have captured biological changes that were more common among those who later developed the disease.

A potential future use could therefore be to use blood tests to identify people who need to be monitored more closely with other examinations.

Weaker Signals for Breast Cancer

The researchers also observed changes in women who later developed breast cancer. Such patterns could be detected about 1.5 to eight years before diagnosis.

The differences, however, were less clear than for prostate cancer, which means that the method in its current form does not have sufficient accuracy to be used as an independent screening test. Instead, the results suggest that the technique could in the future be combined with other risk factors and examinations.

Looking for the Body’s Early Reaction

Many blood-based cancer tests try to detect small amounts of DNA that the tumor itself has released into the blood. This is difficult at a very early stage of cancer because a small tumor can release extremely tiny quantities of tumor DNA.

The researchers behind the new study are instead investigating broader changes in DNA methylation. The idea is that the body may start to change biologically long before a tumor is large enough to cause symptoms or be detected by conventional methods.

If such changes can be measured reliably, it could potentially make it possible to identify an increased cancer risk much earlier than today.

Not a Finished Cancer Test

However, the results do not mean that a routine blood test can already predict who will develop cancer eight years in advance.

The study is retrospective. The researchers knew afterward which participants eventually developed cancer and were then able to look for differences in their older blood samples. For the method to be used in healthcare, larger prospective studies are required, where people are followed forward in time without the researchers already knowing who will develop the disease.

The researchers also need to determine how often the method gives false alarms and how well it works in much larger and more diverse patient groups.

But the results show that blood can contain measurable biological signals long before a cancer diagnosis is made. If the technique can be validated, future screening could therefore involve not only finding already developed tumors, but also identifying people who should be followed closely long before the disease would otherwise be discovered.