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Diagnostics

Adhesive tape–based method could help screen skin cells for melanoma

A scanning electrochemical microscope can detect a cancer biomarker in skin cells collected with sticky tape, no scalpel needed

by Lauren Gravitz, special to C&EN
October 14, 2019

20191014lnp3-tape1.jpg
Credit: Anal. Chem.
The electrode from a scanning electrochemical microscope sweeps over a sample of skin cells stuck to a piece of adhesive tape, picking up changes in electric current from tyrosinase tagged with an enzyme (light gray circles) via a pair of antibodies (green and dark gray Y-shaped molecules). Tyrosinase is overexpressed in melanoma cells (red) compared with healthy cells (blue).

Melanoma is the deadliest form of skin cancer and not something on which dermatologists like to take chances. When they see a suspicious-looking mole on the tip of a patient’s nose, they biopsy it and send it off for testing. But those biopsies come back negative at least 75% of the time—good news, but at the price of a snip and occasional scar. Now, researchers are aiming to decrease the need for biopsies by turning to a screening method that uses adhesive tape. The tape pulls off a layer of cells and then gets put through a scanning electrochemical microscope (SECM) to check for a known melanoma biomarker (Anal. Chem. 2019, DOI: 10.1021/acs.analchem.9b02819).

One company, DermTech, currently markets an adhesive tape to physicians that screens for melanoma via known genetic mutations. But once the sample is collected, the tape must be mailed to a lab where the cells are removed and tested for overexpression of melanoma-specific genes. Also, this approach loses all information about size and shape of the tumors. The new approach, says Hubert H. Girault of the Swiss Federal Institute of Technology, Lausanne, allows cells to stay in place on the tape, acting as a map of the skin’s surface.

Girault and his colleagues used the adhesive tape from DermTech, adhered it to the skin of mice with different stages of melanoma, circled the location of the lesions on the other side of the tape, and removed it. Then, they created a labeling system to tag tyrosinase, an enzyme that is overexpressed in Stage II melanoma cells and present in high concentrations relative to noncancerous cells. The label links tyrosinase via two antibodies to an enzyme that catalyzes a redox reaction, the results of which can be picked up by the SECM’s sensor as it moves across the tape, indicating the exact location of the tyrosinase. The approach reliably identified Stage II melanomas in 10 out of 10 mice. Detection of earlier stage lesions, however, was less consistent.

Unlike DermTech’s approach, the SECM analysis preserves topological information from the tumors, Girault says. “Because we do imaging, we can see if the spot is growing and if it’s heterogeneous,” which is an indication that the cancer is advancing from one stage to the next. And although they used tape designed for removing skin cells for their analysis, Girault says, “Scotch tape works just as well.”

Ultimately, he and coauthor Andreas Lesch of the University of Bologna envision that people could collect the sample at home. “If you suspect something on your own body,” Girault says, “you could put some tape on it, send the tape to the lab and they’ll test it for you.”

While that sounds good in principle, dermatologists are wary. “The technology is exciting, and I’m excited for it to grow and be validated to the point where it could reduce the number of biopsies,” says Ali Hendi, a dermatologist in Chevy Chase, Maryland, and author of the Atlas of Skin Cancers. He notes that there is room for such a screening test, but it needs to be proved extensively. “The gold standard is a biopsy,” he says. “The worst fear of a dermatologist is to miss a melanoma and for that melanoma to become advanced and kill a patient. To get around that, the test really has to be validated, and the false negative has to be really low.”

Screening technologies, particularly ones administered outside a clinic, say Hendi and other dermatologists, are no match for an in-person visit with a physician who knows what to look for and could quickly perform a biopsy or even a noninvasive exam such as dermatoscopy, a newer technique that uses polarized and nonpolarized light to examine skin surface structure and pigmentation.

In areas where dermatologists are in short supply and it takes months to get an appointment, however, the calculus changes. “In areas where access is an issue, it could be helpful,” says Vishal Patel, a dermatologist and oncologist at the George Washington University School of Medicine and Health Sciences. But, he notes, “screening tests like this need to be administered by a clinician…not [performed] in lieu of one.”

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