New Test Can Spot a Single Prostate Cell in Blood
Ask scientists which they'd rather try to find--a prostate cell in a blood sample, or a needle in a haystack -- and the answer might have been a toss-up. Until now: A remarkable new technique, developed at Hopkins, allows scientists to isolate a single cell from a milliliter of blood -- a feat indeed, considering that in this dollop (about one-fifth of a teaspoon) of blood are some 6 million cells.
"The whole technology of being able to isolate single cells out of the bloodstream is a major breakthrough," says urologist Alan Partin, M.D., Ph.D., who helped develop the technique. This research, published in the Journal of Urology, used the technique to answer a question that had long worried physicians and patients: Is it possible that the act of removing the prostate, or even removing some tissue in a biopsy, might somehow allow prostate cancer cells to escape into the bloodstream? The answer was reassuring -- most likely, no, "and if some cells do break free, it's not significant." (The existence of cancer cells in the blood doesn't mean that a man's cancer is not curable, because these cells must also develop aggressive techniques that will permit them to live in a new, hostile environment outside the prostate.)
But the technique can also answer questions in men after surgery: "Are there still prostate cells floating around, and if so, are they cancer cells? That's what this test allows you to know. We can tell if it's a prostate cell, we can tell if it's cancerous." The test accomplishes what another promising technique has not been able to deliver: That test, called RT-PCR, designed to hone in on PSA, searched for " a piece of DNA that looked like it might have come from a prostate cell.," explains Partin. But RT-PCR tests have not proved terribly reliable; there were many "false positives," and some scientists worried that the test might be measuring a molecule that bears a striking resemblance to PSA, but isn't.
The new test uses tiny magnetic beads, coated with antibodies, that act as flypaper: "They attach to the white blood cells and remove them," says Partin. "Whatever's left is stained for PSA, which lights up in a fluorescent field. Everything else is black, and there's that big prostate cell beacon shining at you." Partin envisions using the technique as a follow-up monitoring test, perhaps as part of routine PSA tests after surgery, to detect any stray prostate cells as soon as possible. Part of his research was funded by CaPCure.FURTHER READING
Polascik, et al. Journal of Urology. Vol. 162:
Tso, et al., Urology, 1997. Vol. 49: 881-885.