CHICAGO--The Truquant BR RIA blood test (manufactured by Biomira
Diagnostics, Inc.) has been shown to be a highly specific predictor
of recurrent breast cancer. In clinical trials, positive test
results predicted relapse 83% of the time, providing as much as
a 12-month (average, 5 month) warning over clinical symptoms and/or
other diagnostic methods for breast cancer recurrence.
The test, which costs about $50, works by detecting the CA27.29
antigen, a tumor marker present in breast cancer cells, said Herbert
Fritsche, PhD, a biochemist and associate professor of laboratory
medicine at M.D. Anderson Cancer Center. He spoke at the the American
Association for Clinical Chemistry meeting.
While the normal gene product is heavily glycosylated and does
not allow for antibody recognition, the tumor mucin gene product
lacks glycosylation and opens at sites that then act as the basis
for monoclonal antibody detection. As breast cancer metastasizes,
glycoprotein is shed into the bloodstream in high levels, alerting
clinicians to a recurrence.
The Truquant BR test was evaluated in a 3-year multicenter, double-blind
prospective study of 166 previously treated patients with stage
II or III breast cancer; all were clinically free of disease at
the time of enrollment. Over the course of 2 years, cancer recurred
in 26 women. Sensitivity of the blood test in predicting recurrence
was 58%, specificity was 98%, positive predictive value was 83%,
and negative predictive value was 93%.
Approved Last April
"This was very striking data," Dr. Fritsche said. "In
fact, it convinced the FDA to approve the test last April despite
the small number of patients." The test was approved for
use in previously treated patients with stage II or III breast
cancer in conjunction with other clinical detection methods.
Further research is now being conducted to confirm these preliminary
data, he said. In addition, it has yet to be shown that use of
the antibody test has an impact on breast cancer outcome.