Wednesday, August 20, 2008

The Smell of Cancer

Skin-cancer tumors give off a characteristic odor profile that could be used for early detection.

By Corinna Wu

Smelling skin cancer: An alcohol solution is dripped onto a volunteer's forearm to collect compounds on the skin’s surface. The sample is then analyzed by gas chromatography/mass spectrometry to identify the chemicals present. Credit: Monell Chemical Senses Center

People who are prone to developing skin cancer have to undergo frequent exams and biopsies of suspicious moles in order to catch tumors at an early stage. But a new finding suggests a quicker, noninvasive method for detection. Scientists have identified a characteristic odor profile given off by skin-cancer tumors, which might one day allow diagnosis by a wave of a detector across the skin.

In the United States, more than a million skin cancers are diagnosed each year. Basal cell and squamous cell carcinomas are the most common types, although they rarely spread and usually are not fatal. Melanoma, which accounts for less than 5 percent of skin-cancer cases, causes the majority of skin-cancer deaths.

Scientists have long surmised that tumors give off a unique smell, thanks to studies showing that dogs have the ability to sniff out melanomas and other cancers. For example, Armand Cognetta, a dermatologist in Tallahassee, FL, trained a dog to find melanoma samples hidden around a room, as well as detect melanomas on skin-cancer patients. "The dogs were definitely smelling something, and nobody has been able to pinpoint what it could be," says Michelle Gallagher, formerly a postdoctoral researcher at the Monell Chemical Senses Center, in Philadelphia, and now a senior scientist at Rohm & Haas, a materials company in Spring House, PA.

So Gallagher and her advisor, Monell chemist George Preti, set out to identify the odor markers. Working with dermatologists at the University of Pennsylvania, Gallagher and Preti recruited 11 people with basal cell carcinoma for the study, as well as controls matched for age, gender, and ethnicity. The volunteers went through a weeklong "wash-out" process in which they used fragrance-free shampoo and soap and wore T-shirts provided by the researchers to eliminate odors from external sources.

The researchers then collected odor samples by placing a funnel with an absorbent fiber over the volunteers' skin for 30 minutes. They also washed the skin with an alcohol solution to collect compounds sitting on the surface. "We found two chemicals in particular that were significantly different when you compared a cancer patient with a healthy subject," Gallagher says. Both compounds were present in the healthy volunteers, but one compound was at a higher concentration and the other at a lower concentration above the tumors in the cancer patients. The researchers presented their findings at the American Chemical Society meeting in Philadelphia.