New technology could smell skin cancer before it turns deadly.
The smell of skin cancer. I'm Bob Hirshon and this is Science Update.
On a previous show, we told you how dogs can detect cancer with their noses. Now those dogs have inspired new technology that tests for skin cancer based on odorants given off by the skin.
Analytical chemist Michelle Gallagher and her colleagues collect these odorants and analyze them using an instrument called a gas mass spectrometer. They identified 92 different chemicals. Then they compared the concentrations of these chemicals in healthy subjects to those of people with skin cancer.
We found that there were two compounds in particular that varied in concentration when compared to the healthy subjects. One was higher and one was lower in concentration.
She says analyzing odorant concentrations could one day become part of routine skin cancer screening at your doctor’s office. I’m Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
In case you missed the "previous show” to which this story refers, you can listen to it here. It was broadcast in February 2006, and described experiments in which dogs were trained to smell cancer on a patient's breath. At the time, no one knew what the dogs were actually smelling, only that they could reliably tell the difference between someone who had cancer and someone who didn't.
This might sound weird, but remember, a “smell” is just another word for airborne chemicals. When those chemicals float into your nose, they trigger nerve receptors that send electrical signals to your brain. In response, your brain creates the sensation of a smell. Different combinations of chemicals produce different electrical patterns, which in turn produce different sensations.
However, the human nose is a poor scientific instrument. It's insensitive to many chemicals, from the oxygen we breathe to toxic carbon monoxide. A cold, an allergy, or an infection can impair its smelling function. Most importantly, it produces a subjective sensation that can't be translated into numbers or teased apart into separate components: if you smell pizza baking, how do you separate the smell of the cheese from that of the sauce and the bread?
In this experiment, scientists placed a funnel with chemical-absorbing fibers over either a cancer patient's skin tumor or a healthy volunteer's skin. (To eliminate odors from outside sources, all volunteers avoided perfume and scented soaps for a week, and wore fragrance-free T-shirts provided by the lab.) After 30 minutes' collection time, the researchers analyzed the chemicals that were trapped in those fibers. They used an instrument called a gas mass spectrometer, which combines two techniques: gas chromatography and mass spectrometry.
The gas chromatograph portion sorts the chemicals by running them through a tube, packed with a solid or liquid filter called a stationary phase. Each chemical travels through the stationary phase at a different rate, depending on the chemical's molecular properties. As each chemical exits the tube, a mass spectrometer converts the molecules into electrically charged ions, accelerates them, and banks them off a magnetic field. The magnetic field deflects lighter ions more than heavier ones. Detectors use this information to determine the mass-to-charge ratio of the ions; this, in turn, reveals the type and abundance of all the chemicals in the sample.
Gallagher's team identified 92 different chemicals in the samples from both groups, but only two were noticeably different in the cancer group compared with the healthy group. Cancer patients' skin emitted more of one chemical and less of another than healthy controls. If the findings hold up, a similar technique could be used to identify skin cancer before it's visible to the naked eye. And this work isn't limited to skin cancer: scientists have been studying the “odor profiles” of all sorts of diseases, in hopes of developing electronic noses that can sniff them out early.
Now try and answer these questions:
- What is a smell?
- What is a gas mass spectrometer? How was it used in this study?
- In what ways is a gas mass spectrometer more useful, scientifically, than a nose?
- Why might cancerous skin produce a different odor profile than healthy skin?
You may want to check out the September 12, 2008, Science Update Podcast to hear further information from Science Update. This podcast's topics include: how bats can hear themselves, why bats and windmills don't mix, why big bird brains evolved faster, and how DEET really works.
Artificial Noses ... and Taste, from the American Association for Artificial Intelligence, is an annotated list of links about sniffing devices, used in a variety of applications from food analysis to disease detection.