February 26, 2009 — A new urine test that detects a gene fusion associated with prostate cancer is highly accurate in detecting the disease, yielding a high specificity relative to biopsy outcome.
The test, known as the T2:ERG urine test, detects the fusion of 2 genes: TMPRSS2 and ERG. It also has a sensitivity that is consistent with the roughly 50% prevalence of these gene fusions in men with prostate cancer.
Test scores also significantly correlate with 4 indicators of prostate cancer aggressiveness.
"The goals for the next generation of prostate cancer tests are not just detection but to distinguish between aggressive and indolent disease," said Jack Groskopf, PhD, director of research and development in the Cancer Diagnostics Division of Gen-Probe Incorporated, in San Diego, California, which developed the test.
He was speaking at a press conference during the 2009 Genitourinary Cancers Symposium, which is cosponsored by the American Society for Clinical Oncology, the American Society for Radiation Oncology, and the Society of Urologic Oncology.
Dr. Groskopf discussed an interim analysis of a prospective study of 556 men scheduled for prostate biopsy who were analyzed with the T2:ERG urine test.
"These are the first results to show that it's feasible to use this test," said Howard Sandler, MD, chair of radiation oncology at the Samuel Oschin Cancer Institute, Cedars-Sinai Medical Center, in Los Angeles, California. Dr. Sandler was not involved in the study, but moderated the press conference.
"This is an amazingly short interval between the discovery [of the gene fusion] and [the emergence of a] possible clinical application in diagnosis," he said. The gene fusions quantified in the test were first reported in 2005.
University of Michigan Lab Innovates Again
The T2:ERG urine test and its potential commercial application are outgrowths of basic science conducted on the fusion of TMPRSS2 and ERG genes at the University of Michigan lab, in Ann Arbor, headed by Arul Chinnaiyan, MD, PhD.
Dr. Chinnaiyan is "one of the leading prostate cancer researchers in the world" and is "brilliant," Dr. Sandler told reporters. The 2 were former colleagues at the University of Michigan.
Among other accomplishments, Dr. Chinnaiyan and colleagues have developed another novel urine test, which assesses levels of prostate-cancer-specific metabolites, for predicting which men have aggressive prostate cancer, as recently reported by Medscape Oncology.
Data Revealed
In the current study, urine specimens were prospectively collected following digital rectal exam from men scheduled for prostate biopsy. Collection sites were the San Diego VA Medical Center, in California, and Université Laval, in Montreal (n = 258), and the University of Michigan (n = 81).
Prostate cancer was detected in 113 of 258 men in the San Diego VA Medical Center/Université Laval study and in 37 of 81 men in the University of Michigan study.
In a quantitative detection of T2:ERG gene fusions in urine, there was an 84% specificity and 43% sensitivity to detection of cancer at biopsy, said Dr. Groskopf.
The 84% specificity favorably compares with a 27% specificity for serum prostate-specific antigen (PSA), and the 43% sensitivity "agrees with" the fact only about 50% of all men with prostate cancer will have T2:ERG gene fusions, he said.
Also, in biopsy tissue (n = 19), T2:ERG mRNA was detected in 11 of 12 (92%) specimens that were gene-fusion positive by fluorescence in situ hybridization.
Furthermore, the T2:ERG urine test significantly correlated with 4 of 5 criteria used to identify aggressive cancer at the time of biopsy: Gleason score (greater than 6); percent of biopsy cores that tested positive for cancer; the amount of cancer found in the biopsy tissue; and cancer significance, which was based on the Epstein criteria, said Dr. Groskopf. The only variable that did not have a significant correlation with the test was PSA density, which is determined by dividing the PSA level by the volume of the prostate.
The next steps for the urine test are to confirm results showing correlation with aggressive cancer and to correlate T2:ERG urine results with pathologic features, such as tumor volume, stage, and grade in prostatectomy tissue, said Dr. Groskopf.
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