MISCAN: estimating lead-time and over-detection by simulation

Estimating the rate of overdiagnosis with prostate cancer screening: evidence from the Finnish component of the European Randomized Study of Screening for Prostate Cancer

PURPOSE

Screening for prostate cancer may have limited impact on decreasing prostate cancer-related mortality. A major disadvantage is overdiagnosis, whereby lesions are identified that would not have become evident during the man's lifetime if screening had not taken place. The present study aims to estimate the rate of overdiagnosis using Finnish data from the European randomized trial of prostate cancer screening.

METHODS

We used data from 80,149 men randomized to a screening or a control group, distinguishing four birth cohorts. We used the "catch-up method" to identify when the difference in the cumulative incidence of prostate cancer between the screening and control groups had stabilized, implying that the screening has no further effect. We define the overdiagnosis rate to be the relative excess cumulative incidence in the screened group at that point. As an independent method, we also examined the diagnosis rates of T1c tumors as an indicator of early tumors detected by PSA.

RESULTS

The estimates of overdiagnosis rates from the catch-up method using the full period of available follow-up ranged between cohorts from 2.3% to 15.4%, and the T1c analysis gave very similar results.

CONCLUSION

Some overdiagnosis has occurred, but there is uncertainty about its extent. A long follow-up is required to demonstrate the full impact of screening. We evaluated the overdiagnosis rates at a population level, associated with being offered screening, taking account of contamination (screening among the controls). The overall evaluation of screening should incorporate mortality benefit, cost-effectiveness, and quality of life.

Prostate Cancer Screening Recommendations for General and Specific Populations in the Western Nations

There is a chaotic scenario that exists in the field of prostate cancer (PCa) screening. To balance goals, such as decreasing mortality, avoiding unnecessary procedures, and decreasing the cost of medical care, the pendulum seems to have swung to the side of more restricted screening. The decrease in PCa screening has led to a slowly creeping decline in the favourable outcomes that existed among patients with PCa. If a potential patient or a family member is trying to get clear guidance about PCa screening by searching the internet, they will end up confused by several recommendations from many organisations. It is even more challenging to obtain any clarity about PCa screening for special populations, such as those with a family history of PCa, those of African descent/African Americans, and the elderly. The advent of genomic medicine and precision medicine is an opportunity to identify those at a very high risk of developing aggressive PCa, so that PCa screening can be more actively undertaken among them. In this paper, the authors review the current recommendations by different entities and summarise emerging molecular markers that may help bring clarity to PCa screening. The authors predict that concrete, consensual guidelines will emerge in less than one decade. Meanwhile, this article suggests intermediary steps that will help save lives from PCa mortality, especially for under-represented populations. This paper is a catalyst to stimulate further discussion and serves as a guide to noncancer-specialists for the near future as precision medicine progresses to better understand risk–benefit and cost–benefit ratios in PCa screening.

Response to the U.S. Preventative Services Task Force decision on prostate cancer screening

The population-level data demonstrate that the inception of prostate-specific antigen (PSA) screening has lowered mortality for prostate cancer over the past 2 decades. However, more recent evidence from randomized trials has presented conflicting results regarding the benefit of PSA screening for prostate cancer mortality. Using available data, the U.S. Preventative Services Task Force recently recommended against PSA screening for prostate cancer. However, prostate cancer continues to kill over 30,000 men annually, and as such, completely abandoning screening for this disease is a disservice to many patients. Rather, the emphasis should be on utilizing evidence-based medicine to reduce overdiagnosis and overtreatment through less frequent screening for low-risk individuals or those unlikely to benefit from screening, halting further screening when appropriate, and utilizing observational strategies in patients unlikely to suffer clinically significant effects of prostate cancer over their anticipated life expectancy.

A stochastic model for survival of early prostate cancer with adjustments for leadtime, length bias, and over-detection

To compare the survival between screen-detected and clinically detected cancers, we applied a series of non-homogeneous stochastic processes to deal with leadtime, length bias, and over-detection by using full information on detection modes obtained from the Finnish randomized controlled trial for prostate cancer screening. The results show after 9-year follow-up the hazard ratio of prostate cancer death for screen-detected cases against clinically detected cases increased from 0.24 (95% CI: 0.16-0.35) without correction for these biases, to 0.76 after correction for leadtime and length biases, and finally to 1.03 (95% CI: 0.79-1.33) for a further adjustment for over-detection. Adjustment for leadtime and length bias but no over-detection led to a 24% reduction in prostate cancer death as a result of prostate-specific antigen test. The further calibration of over-detection indicates no gain in survival of screen-detected prostate cancers (excluding over-detected case as stayer considered in the mover-stayer model) as compared with the control group in the absence of screening that is considered as the mover. However, whether the model assumption on over-detection is robust should be validated with other data sets and longer follow-up.

Targeted prostate cancer screening in men with mutations in BRCA1 and BRCA2 detects aggressive prostate cancer: preliminary analysis of the results of the IMPACT study

OBJECTIVE

To evaluate the role of targeted prostate cancer screening in men with BRCA1 or BRCA2 mutations, an international study, IMPACT (Identification of Men with a genetic predisposition to ProstAte Cancer: Targeted screening in BRCA1/2 mutation carriers and controls), was established. This is the first multicentre screening study targeted at men with a known genetic predisposition to prostate cancer. A preliminary analysis of the data is reported.

PATIENTS AND METHODS

Men aged 40-69 years from families with BRCA1 or BRCA2 mutations were offered annual prostate specific antigen (PSA) testing, and those with PSA > 3 ng/mL, were offered a prostate biopsy. Controls were men age-matched (± 5 years) who were negative for the familial mutation.

RESULTS

In total, 300 men were recruited (205 mutation carriers; 89 BRCA1, 116 BRCA2 and 95 controls) over 33 months. At the baseline screen (year 1), 7.0% (21/300) underwent a prostate biopsy. Prostate cancer was diagnosed in ten individuals, a prevalence of 3.3%. The positive predictive value of PSA screening in this cohort was 47·6% (10/21). One prostate cancer was diagnosed at year 2. Of the 11 prostate cancers diagnosed, nine were in mutation carriers, two in controls, and eight were clinically significant.

CONCLUSIONS

The present study shows that the positive predictive value of PSA screening in BRCA mutation carriers is high and that screening detects clinically significant prostate cancer. These results support the rationale for continued screening in such men.

Empirical estimates of the lead time distribution for prostate cancer based on two independent representative cohorts of men not subject to prostate-specific antigen screening

BACKGROUND

Lead time, the estimated time by which screening advances the date of diagnosis, is used to calculate the risk of overdiagnosis. We sought to describe empirically the distribution of lead times between an elevated prostate-specific antigen (PSA) and subsequent prostate cancer diagnosis.

METHODS

We linked the Swedish cancer registry to two independent cohorts: 60-year-olds sampled in 1981-1982 and 51- to 56-year-olds sampled in 1982-1985. We used univariate kernel density estimation to characterize the lead time distribution. Linear regression was used to model the lead time as a function of baseline PSA and logistic regression was used to test for an association between lead time and either stage or grade at diagnosis.

RESULTS

Of 1,167 older men, 132 were diagnosed with prostate cancer, of which 57 had PSA>or=3 ng/mL at baseline; 495 of 4,260 younger men were diagnosed with prostate cancer, of which 116 had PSA>or=3 ng/mL at baseline. The median lead time was slightly longer in the younger men (12.8 versus 11.8 years). In both cohorts, wide variation in lead times followed an approximately normal distribution. Longer lead times were significantly associated with a lower risk of high-grade disease in older and younger men [odds ratio, 0.82 (P=0.023) and 0.77 (P<0.001)].

CONCLUSION

Our findings suggest that early changes in the natural history of the disease are associated with high-grade cancer at diagnosis.

IMPACT

The distinct differences between the observed distribution of lead times and those used in modeling studies illustrate the need to model overdiagnosis rates using empirical data.

Lead time and overdiagnosis in prostate-specific antigen screening: importance of methods and context

BACKGROUND

The time by which prostate-specific antigen (PSA) screening advances prostate cancer diagnosis, called the lead time, has been reported by several studies, but results have varied widely, with mean lead times ranging from 3 to 12 years. A quantity that is closely linked with the lead time is the overdiagnosis frequency, which is the fraction of screen-detected cancers that would not have been diagnosed in the absence of screening. Reported overdiagnosis estimates have also been variable, ranging from 25% to greater than 80% of screen-detected cancers.

METHODS

We used three independently developed mathematical models of prostate cancer progression and detection that were calibrated to incidence data from the Surveillance, Epidemiology, and End Results program to estimate lead times and the fraction of overdiagnosed cancers due to PSA screening among US men aged 54-80 years in 1985-2000. Lead times were estimated by use of three definitions. We also compared US and earlier estimates from the Rotterdam section of the European Randomized Study of Screening for Prostate Cancer (ERSPC) that were calculated by use of a microsimulation screening analysis (MISCAN) model.

RESULTS

The models yielded similar estimates for each definition of lead time, but estimates differed across definitions. Among screen-detected cancers that would have been diagnosed in the patients' lifetimes, the estimated mean lead time ranged from 5.4 to 6.9 years across models, and overdiagnosis ranged from 23% to 42% of all screen-detected cancers. The original MISCAN model fitted to ERSPC Rotterdam data predicted a mean lead time of 7.9 years and an overdiagnosis estimate of 66%; in the model that was calibrated to the US data, these were 6.9 years and 42%, respectively.

CONCLUSION

The precise definition and the population used to estimate lead time and overdiagnosis can be important drivers of study results and should be clearly specified.

Calibration methods used in cancer simulation models and suggested reporting guidelines

Increasingly, computer simulation models are used for economic and policy evaluation in cancer prevention and control. A model's predictions of key outcomes, such as screening effectiveness, depend on the values of unobservable natural history parameters. Calibration is the process of determining the values of unobservable parameters by constraining model output to replicate observed data. Because there are many approaches for model calibration and little consensus on best practices, we surveyed the literature to catalogue the use and reporting of these methods in cancer simulation models. We conducted a MEDLINE search (1980 through 2006) for articles on cancer-screening models and supplemented search results with articles from our personal reference databases. For each article, two authors independently abstracted pre-determined items using a standard form. Data items included cancer site, model type, methods used for determination of unobservable parameter values and description of any calibration protocol. All authors reached consensus on items of disagreement. Reviews and non-cancer models were excluded. Articles describing analytical models, which estimate parameters with statistical approaches (e.g. maximum likelihood) were catalogued separately. Models that included unobservable parameters were analysed and classified by whether calibration methods were reported and if so, the methods used. The review process yielded 154 articles that met our inclusion criteria and, of these, we concluded that 131 may have used calibration methods to determine model parameters. Although the term 'calibration' was not always used, descriptions of calibration or 'model fitting' were found in 50% (n = 66) of the articles, with an additional 16% (n = 21) providing a reference to methods. Calibration target data were identified in nearly all of these articles. Other methodological details, such as the goodness-of-fit metric, were discussed in 54% (n = 47 of 87) of the articles reporting calibration methods, while few details were provided on the algorithms used to search the parameter space. Our review shows that the use of cancer simulation modelling is increasing, although thorough descriptions of calibration procedures are rare in the published literature for these models. Calibration is a key component of model development and is central to the validity and credibility of subsequent analyses and inferences drawn from model predictions. To aid peer-review and facilitate discussion of modelling methods, we propose a standardized Calibration Reporting Checklist for model documentation.

Psychosocial barriers to active surveillance for the management of early prostate cancer and a strategy for increased acceptance

OBJECTIVES

To review the psychosocial needs of men undergoing active surveillance (AS, the monitoring of early prostate cancer, with curative intervention only if the disease significantly progresses) for prostate cancer, and barriers to its uptake.

METHODS

The introduction of screening for prostate-specific antigen (PSA) has led to more men diagnosed with early and nonlife-threatening forms of prostate cancer; about half of men diagnosed as a result of PSA testing have cancers that would never cause symptoms if left untreated and yet up to 90% of such men receive curative therapy, then living with the toxicity of treatment but with no benefit. Thus AS is increasingly being promoted, but if such a strategy is to succeed, the psychosocial barriers that discourage men from adopting AS must be addressed. We reviewed and assessed reports on this topic, published in English since 1994.

RESULTS

There is relatively little research on AS, as most published reports refer to watchful waiting (which is a palliative management approach). Men with prostate cancer generally have lower levels of psychological disturbance than for other cancers, but the psychosocial issues identified include anxiety in response to no intervention, uncertainty related to loss of control, and lack of patient education and support, particularly around the time of initial treatment planning. Approaches that were identified to improve uptake of AS include increased education and improved communication, interventions to reduce anxiety and uncertainty, and the empowerment of patients by the development of a sense of control and meaning. Physicians attitudes are influential and the education of physicians about AS as an appropriate option is to be encouraged. Peer-support groups were also identified as being of particular value.

CONCLUSIONS

There are several strategies that should be developed if AS is to become more widely adopted. Increased education and good communication can alleviate anxiety and uncertainty, as can interventions for cognitive re-framing. Inviting patients to become active participants in their management might enhance the patients' sense of control, and the involvement of peer-support groups might be beneficial.

Under diagnosis and over diagnosis of prostate cancer

PURPOSE

We quantified the rates of over and under diagnosis of prostate cancer in 2 large patient cohorts during the last 15 years.

MATERIALS AND METHODS

A total of 2,126 men with clinical stage T1c prostate cancer were treated with radical prostatectomy during 1 of the 3 periods 1989 to 1995, 1995 to 2001 and 2001 to 2005. The respective proportions of men with a tumor that met our criteria for over diagnosis (0.5 cm3 or less, confined to the prostate with clear surgical margins and no Gleason pattern 4 or 5) and under diagnosis (nonorgan confined, pathological stage T3 or greater, or positive surgical margins) were examined.

RESULTS

The proportion of men with an over diagnosed tumor was 1.3% to 7.1%. The proportion with prostate cancer that was under diagnosed was 25% to 30%. An ancillary finding was that decreasing the prostate specific antigen threshold for biopsy from 4.0 to 2.5 ng/ml in the screened population resulted in a lower rate of under diagnosis from 30% to 26%, a higher rate of over diagnosis from 1.3% to 7.1% and an increase in the 5-year progression-free survival rate from 85% to 92%. Men who were 55 years or younger were significantly more likely to meet our criteria for over diagnosed cancer.

CONCLUSIONS

Under diagnosis of prostate cancer continues to occur more frequently than over diagnosis. Lowering the prostate specific antigen threshold for recommending biopsy to 2.5 ng/ml resulted in a lower rate of under diagnosis and a higher progression-free survival rate.

Use of modeling to evaluate the cost-effectiveness of cancer screening programs

Cost-effectiveness analysis (CEA) is an analytic tool that provides a framework for comparing the health benefits and resource expenditures associated with competing medical and public health interventions, thereby allowing decision makers to identify interventions that yield the greatest amount of health, given their resource constraints. Models are important components of most, if not all, CEAs, and they play a key role in evaluating the cost-effectiveness of cancer screening programs, in particular. In this article, we describe the basic types of models used to evaluate cancer screening programs and provide examples of the use of models in CEAs and to guide cancer screening policy. Finally, we offer some suggestions for important concepts to consider when interpreting model results.

Tumor characteristics and prognostic factors in two subsequent screening rounds with four-year interval within prostate cancer screening trial, ERSPC Rotterdam

OBJECTIVES

To evaluate the tumor characteristics and prognostic factors in screen-detected prostate cancers in two successive screening rounds with a 4-year screening interval in the European Randomized Study of Screening for Prostate Cancer, section Rotterdam.

METHODS

From 1993 to 2000, 42,376 men (21,210 in the screening arm and 21,166 in the control arm) were randomized and screened. Prostate-specific antigen testing, digital rectal examination, transrectal ultrasonography, and sextant biopsies were offered to the participants in the screening arm. A total of 1218 men with a biopsy indication at the first screening received an additional screening after 1 year (early recall). By 2004, all men had received their second screening. Interval carcinomas were defined as cancers detected during the screening interval and were identified by linkage with the Cancer Registry.

RESULTS

In the first round, 1014 prostate cancers were detected--24 in the men noncompliant to screening, 63 at the early recall screening, and 433 in the second round of screening. Also, 62 interval carcinomas were diagnosed. In the second screening round, the mean prostate-specific antigen value was lower (5.6 versus 11.1 ng/mL), advanced clinical stage T3-T4 was 7.1-fold less common, and 76.4% versus 61.5% of the biopsy Gleason scores were less than 7. In the first screening round, 13 regional and 9 distant metastases were detected; in the second round, 2 cases with distant metastasis were found.

CONCLUSIONS

Overall, a shift toward more favorable tumor characteristics was seen for the second round of screening. These results support the screening methods used and the interscreening interval of 4 years.

Trends in prostate cancer incidence, hospital utilization and surgical procedures, Canada, 1981-2000

BACKGROUND

Numbers of new prostate cancer cases in Canada continue to increase because of increasing prostate cancer incidence, population growth, aging of the population, and earlier detection methods such as PSA (prostate-specific antigen) testing. Concern has been expressed that PSA-related increases in incidence will make unaffordable demands on Canadian hospital resources. Our objective is to relate increases in prostate cancer incidence to trends in hospitalizations and in- patient treatment.

METHODS

Hospitalizations with prostate cancer as primary diagnosis were obtained from the Hospital Morbidity Database, estimates of prostate cancer day surgery from the Discharge Abstract Database, newly diagnosed cases from the Canadian Cancer Registry, and prostate cancer deaths from the Vital Statistics Mortality Databases--all for the years 1981-2000.

RESULTS

Between 1981-2000, the number of new cases rose from 7,000 to 18,500 with a transient peak, 1991-1994. Hospitalizations rose parallel to the incidence until 1991 but then fell sharply in spite of further increasing incidence. The use of radical prostatectomy (RP) increased steadily, but transurethral prostatectomy and bilateral orchiectomy decreased in the 1990s. Decreases in length of stay and in number of hospitalizations resulted in considerably decreased annual hospital days for all prostate cancer in-patient procedures except RP, which remained level since 1993.

CONCLUSIONS

A net decrease in number of in-patient days occurred, despite the increasing number of new prostate cancer cases and the increasing use of radical prostatectomy. We concluded that increases in hospital utilization due to early detection programs, such as PSA testing, are unlikely to overwhelm in-patient services of Canadian hospitals.

Prognostic value of serum markers for prostate cancer

The incidence of prostate cancer has increased dramatically during the last 10-15 years and it is now the commonest cancer in males in developed countries. The increase is mainly caused by the increasing use of opportunistic screening or case-finding based on the use of prostate-specific antigen (PSA) testing in serum. With this approach, prostate cancer is detected 5-10 years before giving rise to symptoms and on average 17 years before causing the death of the patient. While this has led to detection of prostate cancer at a potentially curable stage, it has also led to substantial overdiagnosis, i.e. detection of cancers that would not surface clinically in the absence of screening. A major challenge is thus to identify the cases that need to be treated while avoiding diagnosing patients who will not benefit from being diagnosed and who will only suffer from the stigma of being a cancer patient. It would be useful to have prognostic markers that could predict which patients need to be diagnosed and which do not. Ideally, it should be possible to measure these markers using non-invasive techniques, i.e. by means of serum or urine tests. As it is very useful for both early diagnosis and monitoring of prostate cancer, PSA is considered the most valuable marker available for any tumor. Although the prognostic value of PSA is limited, measurement of the proportion of free PSA has improved the identification of patients with aggressive disease. Furthermore, the rate of increase in serum PSA reflects tumor growth rate and prognosis but, due to substantial physiological variation in serum PSA, reliable estimation of the rate of PSA increase requires follow-up for at least 2 years. Algorithms based on the combined use of free and total PSA and prostate volume in logistic regression and neural networks can improve the diagnostic accuracy for prostate cancer, and assays for minor subfractions of PSA and other new markers may provide additional prognostic information. Markers of neuroendocrine differentiation are useful for the monitoring of androgen-independent disease and various bone markers are useful in patients with metastatic disease.

PSA testing: an evolving relationship with prostate cancer screening

PSA testing has made prostate cancer screening a reality for men in many parts of the world, but its benefit for men's health continues to be debated. In men exposed to PSA testing, there has been a well-documented change in the presentation of prostate cancer with a shift towards earlier pathological stage, not without justifiable concern about over-diagnosis by prostate biopsy. Increasingly, men now diagnosed with early stage cancer have previous PSA exposure and are selected for biopsy based on PSA change in relation to cutoff values. Some recent observations suggest that PSA may no longer be an effective marker for early stage tumours, with PSA elevation failing to discriminate tumour-specific characteristics from benign gland enlargement. Traditionally, variation in pathological stage of clinically localised prostate cancer at diagnosis has related to clinical stage, PSA and biopsy Gleason grade, but with distinctions based upon these three assessments declining and an increasing proportion of organ-confined tumours at presentation, new methods of cancer detection and prognostic assessment are now required. Molecular technologies hold great promise in this respect, and in the future biomarker signatures are likely to overshadow total PSA for guiding early diagnosis and prognostic assessment. While arguments about prostate screening will continue, owing not least to its feasibility, future debate is likely to focus increasingly on technological advances and molecular profiling of these notoriously heterogeneous tumours.