Assessing Benefit and Risk in the Prevention of Prostate Cancer: The Prostate Cancer Prevention Trial Revisited

Model-based cost-effectiveness analyses for prostate cancer chemoprevention : a review and summary of challenges

BACKGROUND AND PURPOSE

Decision-analytic modelling is often used to examine the economics associated with using a specific treatment. As a result, it is important to understand structural and methodological approaches used in published decision-analytic models for examining the cost effectiveness of 5α-reductase inhibitors (5ARIs) for prostate cancer (PCa) chemoprevention. This understanding allows us to provide recommendations for using decision modelling in future economic evaluations of chemoprevention for PCa.

METHODS

A review of the published literature was performed using MEDLINE and the Cochrane Library to identify studies involving mathematical decision models that evaluated 5ARIs for PCa chemoprevention. Published articles were reviewed and key modelling components were extracted and summarized. Recommendations for developing future decision models to examine the economic consequences of PCa chemoprevention were presented.

RESULTS

We identified seven published models of PCa chemoprevention. All the models identified used a Markov framework with time horizons ranging from 4 years to lifetime. Due to the wide range of patient risk groups examined, PCa risk data were taken from the Surveillance, Epidemiology, and End Results (SEER) and other databases or estimates published in relevant clinical trials. Treatment effects included change in the incidence of high- and low-grade PCa and impacts on benign prostate hyperplasia. Adverse events were considered to affect compliance, discontinuation and quality of life. Quality-of-life impacts were similar among studies. Examination of modelling parameter sensitivities was comprehensive.

CONCLUSIONS

Published models have examined the cost effectiveness of PCa chemoprevention; however, limitations exist. Decision models should take into account the full PCa clinical pathway when compiling health states. The time horizon should be long enough to consider the full benefit of chemoprevention while allowing actual time receiving the drug to occur from the start of the model until a man's life expectancy is less than 10 years. Baseline PCa risk should be specific to the population of concern. Models should examine the impact on both low- and high-grade tumours and account for the impact of 5ARIs on benign prostatic hyperplasia. Because chemoprevention has an upfront effect, the structure of the model should be constructed so that the downstream effect of avoiding or delaying recurrence can be considered. Adverse events due to chemoprevention should be considered through compliance, discontinuation or quality-of-life impact, and understanding the impact of avoiding PCa and benign prostatic hyperplasia events are important model properties.

Use of 5-alpha-reductase inhibitors for prostate cancer chemoprevention: American Society of Clinical Oncology/American Urological Association 2008 Clinical Practice Guideline

PURPOSE To develop an evidence-based guideline on the use of 5-alpha-reductase inhibitors (5-ARIs) for prostate cancer chemoprevention. METHODS The American Society of Clinical Oncology (ASCO) Health Services Committee (HSC), ASCO Cancer Prevention Committee, and the American Urological Association Practice Guidelines Committee jointly convened a Panel of experts, who used the results from a systematic review of the literature to develop evidence-based recommendations on the use of 5-ARIs for prostate cancer chemoprevention. Results The systematic review completed for this guideline identified 15 randomized clinical trials that met the inclusion criteria, nine of which reported prostate cancer period prevalence. CONCLUSION Asymptomatic men with a prostate-specific antigen (PSA) <or= 3.0 ng/mL who are regularly screened with PSA or are anticipating undergoing annual PSA screening for early detection of prostate cancer may benefit from a discussion of both the benefits of 5-ARIs for 7 years for the prevention of prostate cancer and the potential risks (including the possibility of high-grade prostate cancer). Men who are taking 5-ARIs for benign conditions such as lower urinary tract [obstructive] symptoms (LUTS) may benefit from a similar discussion, understanding that the improvement of LUTS relief should be weighed with the potential risks of high-grade prostate cancer from 5-ARIs (although the majority of the Panel members judged the latter risk to be unlikely). A reduction of approximately 50% in PSA by 12 months is expected in men taking a 5-ARI; however, because these changes in PSA may vary across men, and within individual men over time, the Panel cannot recommend a specific cut point to trigger a biopsy for men taking a 5-ARI. No specific cut point or change in PSA has been prospectively validated in men taking a 5-ARI.

The comparability of models for predicting the risk of a positive prostate biopsy with prostate-specific antigen alone: a systematic review

CONTEXT

The sensitivity and specificity profile of measuring levels of prostate-specific antigen (PSA) to select men for prostate biopsy is not optimal. This has prompted the construction of nomograms and artificial neural networks (ANNs) to increase the performance of PSA measurements.

OBJECTIVE

A systematic review of nomograms and ANNs designed to predict the risk of a positive prostate biopsy for cancer was conducted in order to determine their value versus measuring PSA levels alone.

EVIDENCE ACQUISITION

Medical Literature Analysis and Retrieval System Online (U.S. National Library of Medicine's life science database; MEDLINE) was searched using the terms "nomogram" "artificial neural network" and "prostate cancer" for dates up to and including July 2007 and was supplemented by manual searches of reference lists. Included studies used an assessment tool to examine the risk of a positive prostate biopsy in a man without a known cancer diagnosis. Intramodel comparisons with evaluation of PSA levels alone, and intermodel comparisons of area under the curve (AUC) from receiver operating characteristic (ROC) curves were conducted. Individual case examples were also used for comparisons.

EVIDENCE SYNTHESIS

Twenty-three studies examining 36 models were included. With the exception of two studies, all the models had AUC values of 0.70 or greater, with eight reporting an AUC of >/=0.80 and four (all ANNs) reporting an AUC >/=0.85, with variable validation status. Fourteen studies compared the AUC with PSA levels alone: all showed a benefit from using AUCs which varied from 0.02 to 0.26. Of the 16 external validation comparisons, in 13 the AUC was lower in the external population than in the model population.

CONCLUSIONS

Nomograms and ANNs produce improvements in AUC over measurement of PSA levels alone, but many lack external validation. Where this is available, the benefits are often diminished, although most remain significantly better than with evaluation of PSA levels alone. In men without additional risk factors, PSA cutoff values alone provide a relatively precise risk estimate, but if additional risk factors are known, PSA values alone are less accurate.

Low-Activity V89L Variant in SRD5A2 Is Associated with Aggressive Prostate Cancer Risk: An Explanation for the Adverse Effects Observed in Chemoprevention Trials Using 5-Alpha-Reductase Inhibitors

OBJECTIVE

The 5-alpha-reductase type 2 (5A2) enzyme catalyses the irreversible conversion of testosterone to dihydrotestosterone, the most active androgen in the prostate. This key enzyme in prostate gland physiopathology has recently been targeted by using inhibitors for chemoprevention of prostate cancer. However, some controversies have arisen by the observation of greater than expected high-grade tumours in men diagnosed with prostate cancer in the finasteride chemoprevention trial. To help understand the impact of prolonged exposure to low 5A2 activity on prostate cancer risk, we analysed the rather common genetic V89L polymorphism, which has previously been well characterised functionally for determining low enzymatic activities.

METHODS

The study was performed on 1605 white Caucasian French men categorised in 803 patients with prostate adenocarcinoma and 802 matched healthy male controls. The different alleles and genotypes were analysed according to case-control status and the aggressiveness pattern of the tumours.

RESULTS

The V89L amino acid substitution leading to the homozygous genotype LL increased the risk of clinically significant disease (odds ratio [OR]=1.89, 95% confidence interval (%95 CI), 1.07-2.74; p=0.0017) and was also associated with the most aggressive patterns of the disease (OR=2.56, 95%CI, 1.41-4.63; p=0.002).

CONCLUSIONS

Our data confirm in a large and homogeneous Caucasian French population that the low-activity V89L variant is associated with an increased risk of aggressive prostate cancer. These results corroborate that long-term exposure to 5A2 inhibitors (chemoprevention) must be evaluated in terms of risk of prostate cancer adverse effects.

Das „Prostate Cancer Prevention Trial“ (PCPT)

The Prostate Cancer Prevention Trial (PCPT) has been the first interventional trial directly aimed at the prevention of prostate cancer. A total of 18,882 men over 55 years with a PSA serum level less than 3.0 ng/ml were randomized to receive either the 5-alpha-reductase inhibitor finasteride 5 mg/day or placebo for 7 years. Despite a 25% reduction of prostate cancers in the treatment arm the results were discussed controversially. This criticism was mainly due to the observation of significantly more high-grade cancers in the finasteride group. Meanwhile, results of extensive follow-up analyses have been published suggesting that this finding is most likely due to optimized tumor detection in smaller glands. Further work-up demonstrated that PSA diagnosis and the histopathological examination were not compromised by finasteride. Furthermore, in addition to a decrease of prostate cancer the amount of prostatic intraepithelial dysplasia (PIN) was also reduced under finasteride. Future research must now aim at defining high-risk groups specifically profiting from chemoprevention with a 5-alpha-reductase inhibitor.

Prediction of Prostate Cancer for Patients Receiving Finasteride: Results From the Prostate Cancer Prevention Trial

Purpose

Using data from men in the finasteride group of the Prostate Cancer Prevention Trial (PCPT), we evaluated the impact of prostate-specific antigen (PSA) and other risk factors on the risk of prostate cancer.

Methods

Four thousand four hundred forty men in the finasteride group of the PCPT underwent prostate biopsy, had at least one PSA and a digital rectal exam (DRE) during the year before biopsy, had at least two PSA values from the 3 years before biopsy, and were on finasteride at the time of PSA evaluation. Logistic regression was conducted using the variables age, race, family history of prostate cancer, PSA, PSA velocity, and DRE adjusting for history of prior prostate biopsy.

Results

Six hundred forty-nine (14.6%) of 4,440 men were diagnosed with prostate cancer; 250 had Gleason 7 or higher cancer. Factors associated with an increased risk of prostate cancer included high PSA value and a rising PSA (24.9% risk for PSA value of 1.0 ng/mL and 24.8% risk for a rising PSA), family history of prostate cancer, abnormal DRE result, African American race, and older age. Factors associated with an increased risk of Gleason 7 or higher grade prostate cancer included PSA, abnormal DRE, and older age. A prior negative biopsy was associated with decreased risk of prostate cancer and high-grade prostate cancer.

Conclusion

Risk factors for prostate cancer on biopsy for men receiving finasteride include PSA, DRE, age, race, family history, and history of a prior negative biopsy. With the exception of the approximate reduction of PSA by half with finasteride, the impact of these risk factors is similar to men who do not receive finasteride.

Finasteride as a chemopreventive agent in prostate cancer: impact of the PCPT on urologic practice

Prostate cancer chemoprevention involves the use of natural and/or synthetic agents that inhibit or reverse the development of precancerous lesions or delay progression of these lesions to invasive disease. The recent completion of the first Phase III trial for prostate cancer prevention, the Prostate Cancer Prevention Trial (PCPT) using the drug finasteride, has provided the urologic community with the first evidence that a chemopreventive agent can reduce the risk of developing prostate cancer. The enthusiasm for the clear relative risk reduction in the finasteride arm of the trial has been tempered by the observation that the incidence of high-grade tumors was higher in men receiving finasteride compared to those on placebo. A question remains about whether the observed higher incidence in high-grade tumors is real or whether it is related to a pathologic or sampling artifact. The PCPT has instigated a great deal of debate, resulting in the larger urologic community being reluctant to recommend the widespread use of finasteride as a chemopreventive agent. This review summarizes the PCPT, analyzes its controversial results, and describes future prostate cancer chemoprevention studies.

A new look at the 5alpha-reductase inhibitor finasteride

Finasteride is the first 5alpha-reductase inhibitor that received clinical approval for the treatment of human benign prostatic hyperplasia (BPH) and androgenetic alopecia (male pattern hair loss). These clinical applications are based on the ability of finasteride to inhibit the Type II isoform of the 5alpha-reductase enzyme, which is the predominant form in human prostate and hair follicles, and the concomitant reduction of testosterone to dihydrotestosterone (DHT). In addition to catalyzing the rate-limiting step in the reduction of testosterone, both isoforms of the 5alpha-reductase enzyme are responsible for the reduction of progesterone and deoxycorticosterone to dihydroprogesterone (DHP) and dihydrodeoxycorticosterone (DHDOC), respectively. Recent preclinical data indicate that the subsequent 3alpha-reduction of DHT, DHP and DHDOC produces steroid metabolites with rapid non-genomic effects on brain function and behavior, primarily via an enhancement of gamma-aminobutyric acid (GABA)ergic inhibitory neurotransmission. Consistent with their ability to enhance the action of GABA at GABA(A) receptors, these steroid derivatives (termed neuroactive steroids) possess anticonvulsant, antidepressant and anxiolytic effects in addition to altering aspects of sexual- and alcohol-related behaviors. Thus, finasteride, which inhibits both isoforms of 5alpha-reductase in rodents, has been used as a tool to manipulate neuroactive steroid levels and determine the impact on behavior. Results of some preclinical studies and clinical observations with finasteride are described in this review article. The data suggest that endogenous neuroactive steroid levels may be inversely related to symptoms of premenstrual and postpartum dysphoric disorder, catamenial epilepsy, depression, and alcohol withdrawal.

Chemoprevention of prostate cancer with finasteride

Prostate cancer is a significant cause of disease and death, making it an attractive target for chemoprevention. The association between lifetime exposure to dihydrotestosterone and risk of developing prostate cancer suggests that chemoprevention is possible with 5alpha-reductase inhibition. The recently completed Prostate Cancer Prevention Trial indicates that chemoprevention is possible with the 5alpha-reductase inhibitor finasteride. Development of a cost-effective chemoprevention strategy for prostate cancer is evolving, and is expected to have significant positive economic and public health benefits.

Chemoprevention of prostate cancer

Prostate cancer is an attractive target for chemoprevention because of its ubiquity, treatment-related morbidity, long latency between premalignant lesions and clinically evident cancer, and defined molecular pathogenesis. The Prostate Cancer Prevention Trial has provided the first firm evidence that this cancer can be prevented by a relatively nontoxic oral agent. Additional agents, many of which are antioxidants with antiandrogenic effects, are being tested (or soon will be) in large clinical trials. The current body of evidence is insufficient to make a routine recommendation of any dietary or nutritional supplement for the prevention of prostate cancer.

Male hormonal contraception: concept proven, product in sight?

Current male hormonal contraceptive (MHC) regimens act at various levels within the hypothalamic pituitary testicular axis, principally to induce the withdrawal of the pituitary gonadotrophins and in turn intratesticular androgen production and spermatogenesis. Azoospermia or severe oligozoospermia result from the inhibition of spermatogonial maturation and sperm release (spermiation). All regimens include an androgen to maintain virilization, while in many the suppression of gonadotrophins/spermatogenesis is augmented by the addition of another anti-gonadotrophic agent (progestin, GnRH antagonist). The suppression of sperm concentration to 1 x 10(6)/ml appears to provide comparable contraceptive efficacy to female hormonal methods, but the confidence intervals around these estimates remain relatively large, reflecting the limited number of exposure years reported. Also, inconsistencies in the rapidity and depth of spermatogenic suppression, potential for secondary escape of sperm into the ejaculate and onset of fertility return not readily explainable by analysis of subject serum hormone levels, germ cell number or intratesticular steroidogenesis, are apparent. As such, a better understanding of the endocrine and genetic regulation of spermatogenesis is necessary and may allow for new treatment paradigms. The development of an effective, consumer-friendly male contraceptive remains challenging, as it requires strong translational cooperation not only between basic scientists and clinicians but also between public and private sectors. At present, a prototype MHC product using a long-acting injectable testosterone and depot progestin is well advanced.