Bioengineered Freckle Turns Darker When Detecting Cancer

As soon as the calcium level exceeds a particular threshold over a longer period of time, an implant inserted under the skin triggers the production of melanin. This causes a mole to form. (Re-enacted montage: ETH Zurich)

Scientists have made an implant made of genetically engineered cells that’s designed to detect developing breast, prostate, and colon cancers when they are only a few millimetres in size. Should a tumour develop, a visible mole will appear on the skin. 

The ability to detect such tumours reliably and early would not only save lives, but also reduce the need for expensive, stressful treatment.


“[The implant] is intended primarily for self-monitoring, making it very cost-effective.”


The research team, working with Martin Fussenegger of the Swiss Federal Institute of Technology in Zurich have genetically altered human skin cells that would become darker in colour when exposed to rising calcium levels. Their work is described in the journal Science Translational Medicine.

The early warning system comprises a genetic network that biotechnologists integrate into human body cells, which in turn are inserted into an implant. This encapsulated gene network is then implanted under the skin where it constantly monitors the blood calcium level.

As soon as the calcium level exceeds a particular threshold value over a longer period of time, a signal cascade is triggered that initiates production of the body’s tanning pigment melanin in the genetically modified cells. The skin then forms a brown mole that is visible to the naked eye.


The mole appears long before the cancer becomes detectable through conventional diagnosis.

“An implant carrier should then see a doctor for further evaluation after the mole appears,” explains Fussenegger. It is no reason to panic. “The mole does not mean that the person is likely to die soon,” he stresses. It simply means that clarification and if necessary treatment is needed.

The researchers used calcium as the indicator of the development of the four types of cancer, as it is regulated strongly in the body. Bones serve as a buffer that can balance out concentration differences. However, when too much calcium is detected in the blood, this may serve as a sign for one of the four cancers.

“Early detection increases the chance of survival significantly,” says Fussenegger. For example, if breast cancer is detected early, the chance of recovery is 98 percent; however, if the tumour is diagnosed too late, only one in four women has a good chance of recovery. “Nowadays, people generally go to the doctor only when the tumour begins to cause problems. Unfortunately, by that point, it is often too late.”

The implant also has an additional advantage: “It is intended primarily for self-monitoring, making it very cost effective,” he explains.

However, for those who would prefer not to deal with the constant stress, an implant can also be used that develops a mark visible only under a red light. “This regular check could be carried out by their doctor.”

The disadvantage is that the service life of such an implant is limited, as Fussenegger has found in literature. “Encapsulated living cells last for about a year, according to other studies. After that, they must be inactivated and replaced.”

So far, this early warning system is a prototype that’s been tested in a mouse model and on pig-skin. It functioned reliably during these tests, where moles developed only when the calcium concentration reached a high level. 

With a long way to go before testing it on humans, Fussenegger says that the concept of the “biomedical tattoo” could also be applicable to other gradually developing illnesses, like neurodegenerative diseases and hormonal disorders. In principle, the researchers could replace the molecular sensor to measure biomarkers other than calcium.

“Continued development and clinical trials, in particular, are laborious and expensive, which we as a research group cannot afford,” he says. 

Fussenegger estimates that bringing such a cancer diagnosis implant to market maturity will take at least 10 years of research and development.