Researchers in the US have invented small, sponge-like implant that can detect and trap circulating tumour cells (CTCs) in the bloodstream. Breaking off from the primary tumour to grow elsewhere in the body, such as in the bones, liver, or lungs, CTCs can be difficult to detect until a new tumour has formed, with some patients displaying no symptoms at all until it's too late.

The device has so far only been tested in mice with breast cancer, but the team is hoping it will one day speed up diagnosis and treatment in patients with metastasis - the process by which tumour cells spread throughout the body. "Animals receiving an implant had a significantly reduced burden of disease in their lungs relative to animals that did not have an implant," study co-author Lonnie Shea at Northwestern University told AFP.

Pictured above, the biodegradable implant is about 5 millimetres in diameter, and is inserted in either the abdominal fat or just under the skin. The porous material of the implant - which is already used widely in various medical devices - is packed with a signalling molecule called CCL22, which attracts immune cells to accumulate around it and latch on.

These immune cells then attract the CTCs that circulate in small, barely perceptible numbers, and trap them in the sponge's tiny pores. As part of the experiment, mice with breast cancer received two implants each, and after just two weeks, the implants had collected enough CTCs for analysis. 

Not only did the device trap CTCs, which would allow doctors to extract the device with the tumour cells inside for a more accurate diagnosis, but when the team compared the numbers of CTCs in mice with and without the implant, they found that the implant had successfully reduced the number of CTCs that migrated to secondary sites from the initial tumour. 

"The combined systems can enable the early detection of metastatic disease," Shea told Discovery News. "The initial benefit is detection - catching the metastasis before it spreads widely throughout the body. However… the opportunity to reduce [the] burden (of cell spread) can potentially extend the period of time over which therapies may be effective."

The team has also now figured out how to detect tumour cells in the device while it's still implanted, using a new scanning technique called optical coherence tomography (OCT). "This technique, which can penetrate living tissue by a few millimetres, involves measuring the way light is scattered off large molecules and structures inside cells," Clare Wilson reports for New Scientist. "Cancer cells can be detected because they are denser internally. Various firms are developing devices that would let OCT be done with a smartphone."

As the cause of 90 percent of human cancer deaths around the world, metastasis is a huge problem for people who are already dealing with cancer. If the researchers can get it working in humans, it won't be enough to clear all the CTCs from the body, but could alert doctors to their presence early enough to start chemotherapy before any new tumours form. 

The main challenge in getting it ready for humans, New Scientist reports, is figuring out how to get the OCT scanner to penetrate human skin, which is thicker than mouse skin.

The results have been published in Nature Communications