Ida Rahmqvist: Circulating tumor DNA analysis could improve the prognosis for children with cancer

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IDA RAHMQVIST
Dissertation defense: 28 May 2025 (click for details)
Doctoral thesis: Personalized analysis of circulating tumor DNA in childhood malignancies
Research area: Pediatrics
Sahlgrenska Academy, The Institute of Clinical Sciences

Every year, about 350 children in Sweden are diagnosed with cancer. The most common subgroups are blood cancer, cancers of the lymphatic system, and brain tumors. The causes of childhood cancer remain largely unknown. While some inherited genetic syndromes can increase the risk of disease, most cases are thought to result from spontaneous genetic changes or developmental errors during early growth.

Thanks to advances in cancer care, around 85 percent of children with cancer now survive. However, treatments are typically intense and can cause lasting side effects and complications in a young, developing body.

“That’s why it’s important to avoid both over- and undertreatment. We need better tools to evaluate how well a child is responding to therapy—and methods that allow us to closely monitor if the cancer is coming back,” says Ida Rahmqvist, a trained molecular biologist, researcher, and a doctoral student at the Institute of Clinical Sciences. She is part of Martin Dalin’s research group at the Sahlgrenska Center for Cancer Research.

For children with aggressive or metastatic cancers, the outlook is often dismal. If relapses could be detected earlier, doctors might be able to intervene sooner—and potentially improve outcomes.

Circulating tumor DNA analysis offers a window into disease progression

Tiny fragments of DNA from tumor cells - known as circulating tumor DNA, or ctDNA - can be found in the blood.

“By using what's called liquid biopsies - samples taken from fluids such as blood, urine, or spinal fluid - we can measure ctDNA levels. In our study, we analyzed ctDNA in blood samples taken at diagnosis, during treatment, and after treatment in children with cancer.”

First, the researchers sequenced* each child’s tumor DNA to create a panel of ten specific mutations unique to that patient’s cancer. Using an ultra-sensitive sequencing method, they were then able to track ctDNA levels over time, offering valuable insight into how the disease was evolving.

General study design from thesis: Both tumor DNA and the child’s normal DNA are sequenced. Ten tumor-specific mutations are selected to create a personalized sequencing panel. DNA is extracted from blood plasma (Step 1), prepared for sequencing using the personalized panel (Step 2), sequenced (Step 3), and then analyzed to interpret results for each child (Step 4). (Illustration created in BioRender)

Personalized treatment based on ctDNA levels may improve outcomes

The goal of the PhD project was to monitor disease progression in children diagnosed with neuroblastoma (a cancer of the nervous system) and rhabdomyosarcoma (a cancer that develops from muscle cells).

“We’ve been able to show that ctDNA levels correlate with the tumor burden* in children diagnosed with these cancers. By monitoring the levels of circulating tumor DNA in the blood of children with neuroblastoma and rhabdomyosarcoma-, we were in several cases able to detect upcoming relapses well before they could be confirmed by today’s standard clinical methods.”

Their method proved to be highly specific and could complement existing tools used for disease monitoring. If integrated into clinical practice, this technique could help doctors tailor treatments more effectively and track the disease with greater precision - ultimately improving prognosis for children with cancer.

What’s been most rewarding about this PhD project?
“Being part of the development of this method has been incredibly meaningful. Contributing, even in a small way, to research that could one day give children more targeted treatment and better chances of recovery - that’s been deeply fulfilling.”

Text: Susanne Lj Westergren