Blood Test May Detect Cancer Early
A new blood test may someday make it possible for doctors to diagnose cancer even before a patient develops symptoms.
The new test，developed by Dr Jonathan W.Uhr of the University of Texas and his colleagues，is so sensitive that it can detect one cancer cell in a milliliter（毫升）of blood.
“Cancer cells are shed（脱落） from a primary tumor early in the life history of the tumor，”Uhr explained.“The shedding of these cells can be used as a screening test，potentially，for early tumors.”
To identify epithelial（上皮的） cells—cells associated with 80% of cancers—among other cells in the blood，Uhr's team mixed iron particles into blood samples.The particles were coated with substances that react with epithelial cells and caused them to separate from red and white blood cells.Then，under a laser beam，epithelial cells appeared to be a different color from other blood cells，and the researchers could count them using a microscope.
Uhr and his colleagues used this method to test blood from 30 patients with breast cancer，3 patients with prostate（前列腺） cancer，and 13 healthy subjects.Samples from cancer patients showed significantly more epithelial cells than samples from healthy subjects.The research team found epithelial cells even in most cases of early disease，including samples from 12 of the 14 patients whose breast cancer had not spread beyond the breast.
In a separate study，the investigators tested blood samples from eight patients with breast cancer，at various intervals over 1 to 10 months.It showed that the number of cancer cells in the blood fell or disappeared during chemotherapy（化学疗法） and rose again if tumors grew again.
“At this time，we believe the most important test of the usefulness of our method is to screen for early detection of cancers in the general population，” Uhr's group concluded.
“Another objective would be to be able to predict，” said Uhr.“We want to be able to determine when these tumor cells in the blood are aggressive，and treatment is needed，versus when this is a shedding that is harmless.But it will take many，many years and many patients to determine that.” 31. Dr Uhr's new test can be used to find the number of.
A. iron particles in a blood sample
B. epithelial cells in a blood sample
C. blood cells in a blood sample
D. tumors in a human body
32. Uhr's team mixed iron particles into blood samples.
A. to identify red blood cells
B. to separate epithelial cells from red and white blood cells
C. to identify white blood cells
D. to identify the color of cancers
33. In another study，Dr Uhr and his colleagues found that the patients' epithelial cells.
A. would increase if these patients' condition turned better
B. would decrease if these patients' condition turned better
C. didn't change in number
D. had nothing to do with chemotherapy
34. For Dr Uhr and his colleagues，at present，it is most important to.
A. detect breast cancer among women
B. detect prostate cancer among men
C. detect cancers in their early stage among people in general
D. find out how many people have been screened for possible cancers
35. What Dr Uhr said indicates that he and his colleagues are not sure yet.
A. how to kill aggressive tumor cells
B. how to tell an aggressive tumor cell from a harmless shedding
C. if aggressive tumor cells exist
D. if their method is useful