Scientists believed 'junk DNA' served no purpose but a new study says some of it actually helps stop cancer cells from growing

For decades, large stretches of human DNA were written off as genetic clutter, sequences that seemed to do nothing and carry no obvious purpose. Scientists even gave them a name: junk DNA. That label is now looking increasingly embarrassing.

A new study published in the journal Science Advances has found that some of these so-called junk DNA elements have, over millions of years, quietly worked their way into some of the most fundamental biological pathways in the human body, including ones that regulate cancer.

What the researchers looked at


The study was led by researchers from Arizona State University and Tianjin Medical University, along with an international team of collaborators.

The focus was on a class of molecules known as long noncoding RNAs, or lncRNAs. These are genetic elements that do not produce proteins but have increasingly been found to play a role in regulating how genes behave.

Many lncRNAs are unique to humans and other primates, which has drawn growing interest from cancer researchers.

The team analysed around 18,000 lncRNAs across 17 animal species, tracing their origins and biological roles across nearly 500 million years of evolutionary history. Of those, roughly 5,000 were found to be associated with at least one type of cancer.

How junk DNA became something more

What the researchers found was a gradual process. Many of the cancer-associated lncRNAs appear to have started out as small, non-functional RNA fragments. Over time, they expanded in length by absorbing additional genetic material, and eventually became integrated into cellular pathways that evolved hundreds of millions of years ago.

"Our findings suggest that cancer-associated long noncoding RNAs are not simply recent evolutionary additions," said Michael Lynch, professor in the Biodesign Center for Mechanisms of Evolution at ASU and co-author of the study. "Instead, they can gradually become integrated into regulatory systems that have existed for hundreds of millions of years."

The molecule that tells the story

To illustrate how this process works in practice, the team focused on one particular lncRNA called MIR497HG.

The molecule appears to have originated around 29 million years ago in a common ancestor of humans and macaques, beginning as a microRNA before a single DNA mutation triggered short bursts of RNA expression.

After humans and macaques diverged, a longer form of MIR497HG emerged that is unique to humans. As it expanded, it became connected to regulatory networks that are estimated to be around 473 million years old, pathways involved in metabolism, stress responses, and programmed cell death.

Once wired into those ancient systems, the molecule was in a position to influence, or disrupt, them. Researchers say that when MIR497HG is misexpressed, it can contribute to cancer.

What lab experiments showed

The team then tested what happens when MIR497HG is manipulated in the laboratory. Experiments carried out in human stem cells and multiple cancer cell lines found that reducing MIR497HG expression caused cancer cells to grow faster. Restoring its expression did the opposite, suppressing cancer cell growth across multiple cancer types.

The researchers also identified a specific connection between MIR497HG and a regulatory axis in the body known as the AMPK-ferroptosis pathway, suggesting that disruption of this network may contribute to tumour development.

"By combining evolutionary biology with cancer biology, we were able to trace how a young RNA molecule acquired regulatory functions within one of the cell's most ancient signalling networks," said Wen Wei, corresponding author of the study.

What this could mean for cancer research

The findings carry two potential implications for how cancer is studied and eventually treated.

First, MIR497HG could serve as a predictive biomarker. The molecule is expressed at high levels in normal tissue but drops significantly as cancer progresses and in patients with poor clinical outcomes.

Second, the research points to a broader pattern. Many human-specific regulatory RNAs may have gone through a similar evolutionary journey, starting out as neutral, low-key elements before gradually getting wired into existing biological networks and gaining the ability to influence disease.

"Understanding how these regulatory RNAs evolved gives us a new framework for identifying biomarkers and potential therapeutic targets across multiple cancer types," said Wei.

The study was conducted in collaboration with researchers from the University of Chicago, Zhejiang A&F University, Chengdu Neusoft University, and other institutions.