Primary tumors shed cancerous cells, known as circulating tumor cells
(CTCs), into the blood. These have been widely studied as prognostic
biomarkers for various cancers. Because these cells are often larger,
irregularly shaped and tend to cluster together, they get trapped in
smaller vessels.
The authors hypothesized that most cells released from a
gastrointestinal tumor would flow into the portal vein and then get
sequestered by the narrow vessels in the liver. These cells would not
reach the peripheral venous system. CTCs from gastrointestinal tumors
are rarely identified in the peripheral blood until the cancer is widely
metastatic.
The portal vein samples contained far more tumor cells in all stages
evaluated, including locally advanced as well as metastatic tumors. Blood
collected from the portal vein had a mean of more than 100 CTCs per 7.5
milliliters. Patients with less advanced disease, who could potentially
benefit from surgery to remove the tumor, had fewer CTCs. Those patients
averaged about 80 CTCs per 7.5 milliliters.
In contrast, when the researchers used peripheral blood to test the
same patients, they found few, if any, circulating tumor cells. Those
samples contained, on average, less than one CTC in 7.5 milliliters of
blood, the equivalent of one cell in a billion.
"Access to circulating tumor cells may help us define the diagnosis
and guide treatment," Waxman said. "Having the ability to count them and
to probe their molecular profiles can make a substantial difference in
how we treat each patient's tumor."
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