Laser scan of veins detects cancer
20 September 2007
Technology that can detect tumour cells by scanning
surface veins with a laser, eliminating the need for drawing blood, has been
developed by Purdue University researchers.
By shining a laser on surface veins, such as those on the wrist and inside
the cheek, researchers are able to reveal and count circulating tumour
cells. In addition to being less invasive, the new method is able to
evaluate a much larger volume of blood than what can be drawn from a patient
Researchers from Purdue's Cancer Center, Department of
Chemistry and Weldon School of Biomedical Engineering collaborated with
cancer and biotechnology experts from the Mayo Clinic to develop the
"In the initial stages of cancer, there are very few circulating tumour
cells — cells that indicate the spread of cancer and initiate secondary
tumour formation," said Philip Low, Purdue's Ralph C Corley Distinguished
Professor of Chemistry. "By increasing the volume of blood analyzed, we
improve the sensitivity of the test and allow for earlier diagnosis. If
there are two cancer cells in every 50ml of blood, odds are the cells would
not be found in a 10ml blood sample. However, the cells would be found in
the 100ml of blood that flow through large veins each minute."
Optical imaging provides high resolution and chemical specificity for cancer
detection, but it usually suffers from limited penetration depth, making it
hard to reach tumours inside the body, said Ji-Xin Cheng, an assistant
professor of chemistry and biomedical engineering.
"In vivo detection of circulating tumour cells in surface veins provides an
excellent way to overcome this problem," Cheng said.
"Circulating tumour cells provide a benchmark for disease progression and
precise monitoring of their levels could lead to personalized treatment,"
Low said. "This technique allows us to quantify the amount of circulating
tumour cells present, as opposed to tests that provide a 'positive' or
"Through such precise monitoring, a physician could evaluate the response to
chemotherapy and regularly adjust the dosage so that only the exact amount
needed would be administered. This could reduce the time a patient is
treated and the serious side effects that occur."
The technique could provide doctors and patients results in a matter of
minutes and save the medical industry millions of dollars in testing
equipment, said Wei He, a graduate student in the Department of Chemistry
and the Department of Biomedical Engineering. He worked on the project with
Low and Cheng.
By directly labelling tumour cells while they are in the bloodstream, some
of the costs and problems associated with testing drawn blood samples can be
avoided, He said.
"One sample can require five to 10 test tubes during the course of sampling,
processing and analysis such as handling, labelling and washing," He said.
"In addition, large hospitals can have more than 300 cancer patients in one
day. Such a large influx can cause delays in sample processing and delays
can affect the results of analysis."
A paper detailing the technology and detection technique was published in
the July 10 Proceedings of the National Academy of Sciences. In addition to
Low, He and Cheng, postdoctoral researcher Haifeng Wang and Lynn C.
Hartmann, a professor of oncology and associate director for education of
the Mayo Clinic Cancer Center, co-authored the paper.
The technique uses a fluorescent tumour-specific probe that labels tumour
cells in circulation. When hit by a laser, which scans across the diameter
of the blood vessel 1,000 times per second, the tumour cells glow and become
visible. The in-vivo flow detection was performed on a two-photon
fluorescence microscope in Cheng's lab. The researchers compared several
methods and found two-photon fluorescence provides the best signal to
background ratio. The technology is able to scan every cell that is pumped
through the vessel, He said.
Low's team has developed two labelling agents that attach to different forms
of cancer. One label targets ovarian, non-small lung, kidney and endometrial
cancer, and the other targets prostate cancer.
These labels would be administered through an injection. The first label has
already been tested in humans and has no adverse side effects and could
potentially be administered weekly, He said.
Computed tomography, or CT, scans and magnetic resonance imaging, or MRI,
are the current methods used to track the spread of cancer. These methods
have a limited resolution, and a 1mm tumour could go undetected by CT or
MRI. The Purdue-developed technology can achieve single-cell resolution and
can detect rare cell populations.
"Our method can detect cancer cells early in disease development and the
test can be conducted frequently," Low said. "Discovering the cancer early
and knowing whether it has metastasized, or spread, greatly improves a
patient's chance for successful treatment."
The laser penetrates to a depth of 100 microns and is able to examine
shallow blood vessels near the surface of the skin. Advanced optical
technology could be incorporated into the technology platform and enable the
method to reach deeper vessels that handle larger volumes of blood, Cheng
The Purdue team continues to work with the Mayo Clinic and is planning to
initiate a clinical trial to further evaluate the technique. The team also
plans to develop labels for additional types of cancer and to reduce the
size of the equipment to make it portable.
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