A new report in the British Journal of Cancer suggests that data provided through Myriad Genetics’ Prolaris™ test may be “the strongest independent predictor of cancer death outcome yet described” for the management of men with clinically localized prostate cancer.
As our regular readers will be well aware, there is enormous variation in the natural history of prostate cancer among individual patients. The Prolaris test is designed to measures the level of expression level of some 31 genes involved with cell cycle progression (CCP) and then to use to the CCP score to predict disease outcomes over time.
Cuzick et al. have now correlated clinical data (centrally re-reviewed Gleason scores, baseline PSA levels, ages, clinical stages,and extent of disease) with CCP scores for 349 men initally diagnosed with prostate cancer by needle biopsy and managed conservatively over time (i.e., with either active surveillance or watchful waiting). Long-term follow-up data were also available for these 349 patients.
The results of their study show that:
- Based on univariate analysis
- The hazard ratio (HR) for death from prostate cancer was 2.02 for a one-unit increase in CCP score, and this was highly statistically significant.
- The CCP score was only weakly correlated with standard prognostic factors.
- Based on multivariate analysis
- The HR for death from prostate cancer was 1.65 for a one-unit increase in CCP score, and this was still highly statistically significant.
- The patients’ initial Gleason scores and PSA levels provided significant additional contributions.
- The 81 percent of patients with lower CCP scores when left untreated had a 5-year survival rate of 93 percent.
- The 19 percent of men with higher CCP scores when left untreated had a 5-year survival rate of 63 percent and a 10-year survival rate of 44 percent.
In a media release from Myriad Genetics, Jerry Lanchbury, PhD, the chief scientific officer of the company and a co-author of this paper stated that, “We believe this test will provide critical information needed to avoid unnecessary and life altering morbidities associated with treating the disease in men who have a less aggressive form of prostate cancer.”
Once again, we need to note that these data, which are certainly supportive of the potential of the Prolaris test, are based on retrospective rather than prospective study of the value of the test. To be absolutely compelling, we still need to see data from prospective studies of the use of this test, i.e., studies in which the tests is used at the time of diagnosis to project patients’ outcomes over time, with biochemical progression-free, metastasis-free, prostate cancer-specific, and overall survival as the study outcomes.
The cost of the Prolaris test is of the order of $3,400. This may not be excessive for a one-time test if it really can predict with high accuracy the probability of death from prostate cancer in specific individuals, since the costs of many of the tests and of first-line treatment may be saved. However, we have a ways to go before we can say with certainty that the Prolaris test can acuurately differentiate, in a prospective manner, between those men needing first-line treatment and those who can be managed conservatively.
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