Blood Test Explored to Back Up Mammograms
Scientists are testing blood from more than 1,000 women for a protein that might signal breast cancer, hoping to create for women the kind of blood test men have for prostate disease.
It’s too soon to know if the experiment will work. But the quest for new ways to catch early tumors or even precancerous cells--from blood testing to analyzing nipple fluid--is heating up amid controversy over mammograms. Proponents foresee a day when the X-ray routinely comes with a backup test.
“Mammography is not the end-all,” says Dr. Alan Hollingsworth of Oklahoma City’s Mercy Health Center, one of seven U.S. hospitals participating in Matritech Inc.’s blood-test research.
With a hint from another test that a tumor might be forming, “you could look harder. There are ways to look harder than just with mammography.”
Mammograms can detect tumors when they’re tiny, often meaning the difference between surgery that removes or spares the breast. Whether they also save lives is under hot debate. The U.S. government thinks so, and strongly urges women over age 40 to get one at least every other year. Regardless, an estimated third of women don’t get regular mammograms.
Other scientists argue that studies backing mammograms are too flawed to determine if the procedure reduces death.
Mammograms are certainly not perfect. They can miss tumors or flag suspicious spots that turn out to be benign. More powerful imaging techniques, like ultrasound or MRI, can better pinpoint tumors but are too complex and expensive to use on everybody.
The presence of prostate-specific antigen (PSA) protein in men’s blood suggests they may have either an enlarged or cancerous prostate. So why not a blood test for breast cancer?
Nuclear matrix proteins, or NMPs, help form the skeleton of cell nuclei as cells reproduce. Changes in nuclei size or shape can signal cancer. The theory: Different cells use different NMPs, so changes in the type or amount of a certain NMP in the blood could signal cell changes that mean cancer.
Matritech Inc., which licensed rights to NMP research from the Massachusetts Institute of Technology, already sells a test that helps diagnose bladder cancer by finding NMP-22 in urine.
Now Matritech says a related protein, NMP-66, appears specific to breast cancer. In a preliminary study of blood samples from 78 women, NMP-66 was found in everyone with invasive cancer; four of five who had a noninvasive tumor of the milk ducts; and no one with a normal mammogram. The downside: It also was found in two of 24 women with benign breast conditions.
Matritech is looking for NMP-66 in 700 women who will receive biopsies to check for breast cancer, and another 400 women whose regular mammograms show nothing suspicious. Results are expected later this year.
Even if this first clinical trial of NMP-66 is promising, it will take much more research to prove the test works, Hollingsworth cautioned.
Researchers are concerned about those false positives--positive tests that turn out to be benign. It’s not too hard to tell when a mammogram causes a scare, but it will probably take longer to tell if a blood test result is wrong, says Robert Smith of the American Cancer Society.
Ultimately, Matritech hopes to sell NMP-66 as a routine mammogram backup.
There is another breast test, called ductal lavage, that some women are clamoring to get. Doctors put an anesthetic on the nipple and insert a threadlike catheter to flush milk ducts with fluid that dislodges and draws out cells.
Ductal lavage is still experimental. It does not hunt for actual tumors but it can detect abnormal cells that may signal precancerous changes. It is recommended only for women at high risk of getting breast cancer, to help them decide such things as how often to get mammograms or whether to try the drug tamoxifen in hopes of preventing tumors.
Until these experimental tests are better understood, the best advice is to get a regular mammogram from a radiologist who does lots of them--because more experience means more accuracy, says the cancer society’s Smith.
