[Medical Tribune 40(6):15, 1999. ©]
A test to identify the tumor marker telomerase could be a highly specific method of detecting bladder cancer.
Telomerase was detected in the urine specimens of 70 percent of 57 patients with bladder cancer, according to a report in The Journal of Urology (1999:161;388-394).
Sanjay Ramakumar, M.D., a resident physician at the department of urology at the Mayo Graduate School of Medicine in Rochester, MN, and colleagues, compared the accuracy of a telomerase test with tests for other tumor markers and cytology.
The telomerase test was not as sensitive as the test for the bladder tumor antigen BTA stat, which had a detection rate of 74 percent.
But when researchers compared the number of false positives among 139 participants with no evidence of bladder malignancy, they found that telomerase had a specificity rate of 99 percent. By comparison, BTA stat's specificity rate is 73 percent.
Traditionally, doctors have used cytology to make bladder cancer diagnoses. While this method results in a very small percentage of false positives-the study showed a 95 percent specificity rate-it does not detect all malignancies. In the study, just 44 percent of bladder cancers were identified as a result of cytology.
The accuracy of cytology depends on contact between the lesion and urine and the type of cells shed from the lesion. Tumor grade, configuration and location also affect cytology. Tests for BTA stat and telomerase are more sensitive because they identify specific molecular markers.
Joseph A. Smith Jr., M.D., chairman of urologic surgery at Vanderbilt University Hospital in Nashville, TN, said that telomerase did not appear to be an absolute indicator of bladder cancer. "Both BTA and telomerase have significant limitations," he said.
"BTA is more sensitive but we get a large number of false positives. Telomerase is more specific but it has been shown to miss a number of malignancies," he added.
He said that using a combination of cytology, telomerase and BTA probably would result in "a jumble of confusing numbers."