Scientists have made a sponge-like implant that mops up wandering cancer cells. These unassuming little white discs may change the face of cancer detection as we know it.

“This could be the canary in the coal mine,” Lonnie Shea, from the University of Michigan, told New Scientist. 

Shea and a breast cancer surgeon, Jacqueline Jeruss, noticed that patients with breast cancer often came into the hospital because of one common symptom: breathlessness, which indicated that the breast cancer had already spread to the lungs. This prompted the researchers to try to find a way of detecting the spread of cancer cells (called metastasis) before patients exhibit symptoms.

The team created an implant designed to attract cancer cells that have spread from the initial tumor. The findings are published in Nature Communications.

The scaffold-like implant is five millimeters (0.2 inches) in diameter and is made of an inert, porous biomaterial that is already in use in medical devices. It was loaded with a signaling molecule and inserted under the skin or in abdominal fat of mice with a form of breast cancer. Two weeks after insertion, cancer cells were found in the implants. 

The implant acts as bait. The signaling molecule, CCL22, attracts certain immune cells and these in turn recruit metastatic cells (cancer cells on the move), which are "mopped up" by the implant.

The device had some additional benefits for the mice. By capturing cancer cells, it also reduced their presence at other sites around the body. After 28 days the tumor burden in the lung was around 88% lower in mice with the implant.

The researchers also found a way to detect the presence of cancer cells congregating on the implant without needing to remove it. They used a scanning technique (called optical coherence tomography) that can see a few millimeters through biological tissue – just deep enough to scan the implant through mouse skin. The cancer cells can be identified because they have a higher density than healthy cells. The tricky part will be using this image through human skin, which is thicker than mouse skin.

If the technique can be replicated in humans, the implant would be welcomed by doctors everywhere. Scientists have been looking for ways of detecting the spread of cancer cells for a long time. However, they are rare in the blood stream and difficult to detect as a result. This way, doctors could let the implant detect metastasis without needing to actively search for the spreading cells themselves.

There is still a lot more work to be done of course. "We need to see if metastatic cells will show up in the implant in humans like they did in the mice, and also if it's a safe procedure and that we can use the same imaging to detect cancer cells," Shea told the BBC. But even though it has so far only been tested in mice, the results are still very encouraging. 

Shea told New Scientist that the ideal future implant would be one that could be detectable while inside the body – maybe even with a smartphone.