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Analytical Chemistry

Mass Spectrometry Marks Tumor Boundaries

Medical Diagnostics: New technique could guide surgeon's hand during tumor removal

by Laura Cassiday
February 15, 2010

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Credit: Shutterstock
Surgeons could use mass spectrometry to map out where tumors end.
Credit: Shutterstock
Surgeons could use mass spectrometry to map out where tumors end.

When surgeons remove tumors from patients, they excise healthy tissue surrounding the tumor to ensure that no cancer is left behind. But because cancer cells aren't easy to spot with the naked eye, surgeons must wait for a pathologist to check tissue samples before finishing an operation. Now a new tool that combines mass spectrometry with laser surgery could make identifying tumor margins faster and easier (Anal. Chem., DOI: 10.1021/ac102613m).

During conventional cancer surgery, the pathologist examines excised tumor tissue while the patient remains anesthetized on the operating table. The pathologist freezes the tissue, slices it into thin sections, mounts them on microscope slides, and then stains the tissue sections with dyes that distinguish cancerous and healthy tissues. Typically, the surgeon must wait 30 to 40 minutes before the pathologist telephones with an assessment, says Zoltán Takáts, a chemist at Justus Liebig University in Giessen, Germany.

How long a patient can stay under anesthesia limits the number of tissue samples that can be tested during an operation. To detect cancer cells more efficiently, Takáts and his colleagues developed a technique to quickly analyze tumor samples in the operating room with laser desorption/ionization mass spectrometry.

The researchers analyzed liver tissue excised from a cancer patient that contained a colon-cancer metastasis. They fired an infrared laser at spots on the tissue to ionize phospholipids from those regions. The heat of the laser caused the phospholipid ions to form an aerosol, and an air pump pulled the aerosol through a flexible tube to the inlet of a mass spectrometer. In 2009, Takáts developed a similar technique that used electrodes to ionize tissue molecules for mass spectrometry analysis.

Takáts and his colleagues fed the data into a statistics computer program and discovered that it could distinguish between healthy and cancerous tissues based on the types and amounts of phospholipids present. With this technique, the investigators could precisely delineate the boundaries of the cancer, diagnosing each sampling point in less than a second.

The team has also integrated the technique with laser surgery for real-time analysis. The mass spectrometer analyzes the aerosols produced as the laser excises the tissue, Takáts says. "Whenever the instrument identifies cancer cells, it gives a signal to the surgeon to go back and cut out more tissue," he says. The researchers are testing this real-time technique on skin lesions in dogs, and the Hungarian Scientific and Research Ethics Committee has approved the method for human testing.

Jeffrey Pinco, a pathologist with Consulting Pathologists of Connecticut, says that the technique would be especially useful for breast tumors, which are difficult to localize by the usual technique because the surrounding fat does not freeze well. Instead, pathologists must examine the tissue after the operation, he says. "So this technique has the potential to be revolutionary."

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