Case-control studies of cancer screening: theory and practice

Screening history and risk of death from prostate cancer: a nested case-control study within the screening arm of the Finnish Randomized Study of Screening for Prostate Cancer (FinRSPC)

PURPOSE

We assessed the risk of death from prostate cancer (PCa) in relation to men's screening histories, i.e., screening attendance among men who were offered screening.

METHODS

Men in the Finnish Randomized Study of Screening for Prostate Cancer (FinRSPC) screening arm were invited to up to three screening rounds with the serum prostate-specific antigen (PSA) test at 4-year intervals during 1996-2007. Case subjects (n = 330) were men who died from PCa. Each case was matched to five controls (n = 1544) among the men who were free of PCa. Screening history was defined as (1) never/ever attended screening prior to the case diagnosis; (2) attended at the first screening round; and (3) recency of screening, calculated as the time from last screening attendance to the date of case diagnosis. The association between screening history and the risk of death from PCa was estimated by odds ratios (OR) with 95% confidence intervals (CI) using conditional logistic regression.

RESULTS

Having ever attended screening versus never attended was associated with a reduced risk of PCa death (OR 0.60, 95% CI 0.45-0.81) and a similar association was found for those attended (versus not attended) the first screening round (OR 0.67, 95% CI 0.51-0.87). The effect by time since last screen for the risk of PCa death was significantly lower 2-7 years since last screen.

CONCLUSION

Among men invited to screening, subjects who attended any PSA screening during the previous 19 years had a 40% reduction in PCa mortality compared to non-screened men.

International variation in the prevalence of preclinical colorectal cancer: Implications for predictive values of noninvasive screening tests and potential target populations for screening

Screening for colorectal cancer (CRC) is implemented in an increasing number of countries. We aimed to assess international variation in the prevalence of preclinical CRC and the resulting variation in positive and negative predictive values (PPVs, NPVs) of existing and potential CRC screening tests in various countries. Using age‐ and sex‐specific CRC incidence data and transition rates from preclinical to clinical CRC we estimated overall and age‐ and sex‐specific prevalence of preclinical CRC in the target population aged 50–74 years in different parts of the world. These prevalence estimates were used to derive PPVs and NPVs for existing and potential noninvasive screening tests with varying levels of sensitivity and specificity. Within all regions and countries, prevalence strongly increases with age and is higher in men than in women. In addition, major variation was seen between regions and countries, with overall prevalence varying between 1 and 0.1%. As a result, PPVs are expected to strongly vary between ∼10% for men in high incidence countries, such as Australia and Germany, and 1% for women in low incidence countries, whereas NPVs are expected to be consistently well above 99%. Variation in CRC prevalence profoundly affects expected PPVs of screening tests, and PPVs should be carefully considered when decisions on screening tests and strategies are made for specific populations and health care systems. Here, we provide estimates of preclinical CRC and expected PPVs and NPVs of noninvasive screening tests, which may enhance the empirical basis for planning of population‐based CRC screening strategies.

What's new?

Colorectal cancer (CRC) screening is implemented in an increasing number of countries, usually in a two‐step approach consisting in a noninvasive test followed by colonoscopy in case of a positive result. Prevalence of preclinical colorectal cancer strongly affects screening efficiency, but such data is scarce. Here, the authors provide detailed age‐ and sex‐specific preclinical CRC prevalence estimates for various countries and geographical regions and show their implications on expected positive and negative predictive values of existing and potential noninvasive screening tests. Knowledge of these predictive values should enhance the empirical basis for decisions on CRC screening tests and target populations.

Effect of population breast screening on breast cancer mortality to 2005 in England and Wales: A nested case-control study within a cohort of one million women

Objectives

To evaluate the effectiveness of the NHS breast screening programme (NHSBSP) on breast cancer mortality in England and Wales and to compare findings with a cohort analysis of the same underlying population.

Methods

A nested case-control study within a cohort of 959,738 women in England and Wales aged 49–64 who were eligible for routine NHSBSP screening during 1991–2005. Cases who died from breast cancer in 1991–2005 were matched to controls without breast cancer at the case diagnosis date and alive when the case died. Risk of breast cancer mortality associated with intention to screen (ITS) (7047 cases/28,188 controls) and screening attendance (4707 cases/9413 controls) was examined. Bias was minimised in accordance with currently advocated best practice. Odds ratios (ORs) were calculated using conditional logistic regression. Results were compared with findings from an incidence-based breast cancer mortality cohort analysis.

Results

ITS was associated with a 21% breast cancer mortality reduction (OR = 0.79, 95% confidence interval [CI]: 0.71–0.88, P < 0.001). Attendance ≤5 years before diagnosis was associated with a 47% reduction in breast cancer mortality after self-selection correction (OR = 0.53, 95% CI: 0.46–0.62, P < 0.001). Breast cancer mortality reduction associated with ITS was 21% in both the case-control and cohort analyses, but the impact of attendance was marginally greater in the case-control analysis (36% vs. 32%).

Conclusions

Case-control studies designed and analysed according to current best practice guidelines offer an effective means of evaluating population breast screening.

Effectiveness of the Korean National Cancer Screening Program in Reducing Gastric Cancer Mortality

BACKGROUND & AIMS

It is not clear whether screening for gastric cancer by upper endoscopy or upper gastrointestinal (UGI) series examinations (looking at the upper and middle sections of the gastrointestinal tract by imaging techniques) reduces mortality. Nevertheless, the Korean National Cancer Screening Program for gastric cancer was launched in 1999 to screen individuals 40 years and older for gastric cancer using these techniques. We evaluated the effectiveness of these techniques in gastric cancer detection and compared their effects on mortality in the Korean population.

METHODS

We performed a nested case-control study using data from the Korean National Cancer Screening Program for gastric cancer since 2002. A total of 16,584,283 Korean men and women, aged 40 years and older, comprised the cancer-free cohort. Case subjects (n = 54,418) were defined as individuals newly diagnosed with gastric cancer from January 2004 through December 2009 and who died before December 2012. Cases were matched with controls (subjects who were alive on the date of death of the corresponding case subject, n = 217,672) for year of entry into the study cohort, age, sex, and socioeconomic status. Odds ratios (ORs) and 95% confidence intervals (CIs) were obtained via conditional logistic regression analysis.

RESULTS

Compared with subjects who had never been screened, the overall OR for dying from gastric cancer among ever-screened subjects was 0.79 (95% CI, 0.77-0.81). According to screening modality, the ORs of death from gastric cancer were 0.53 (95% CI, 0.51-0.56) for upper endoscopy and 0.98 (95% CI, 0.95-1.01) for UGI series. As the number of endoscopic screening tests performed per subject increased, the ORs of death from gastric cancer decreased: 0.60 (95% CI, 0.57-0.63), 0.32 (95% CI, 0.28-0.37), and 0.19 (95% CI, 0.14-0.26) for once, twice, and 3 or more times, respectively.

CONCLUSIONS

Within the Korean National Cancer Screening Program, patients who received an upper endoscopy were less likely to die from gastric cancer; no associations were found for UGI series.

Effectiveness evaluation of organized screening for esophageal cancer: a case-control study in Linzhou city, China

In China, esophageal cancer has remained a large burden, and endoscopic screening is expected to reduce esophageal cancer mortality. Therefore, a population-based case-control study was conducted to evaluate the effect of screening. Cases were defined as individuals who had died of esophageal cancer, and controls were residents from the same area (three per case) who had not died of esophageal cancer, matched by gender and birth year. The exposure status (whether cases and controls had ever attended the screening or not) was acquired by inspecting the well documented screening records. A conditional logistic regression model was used to estimate the odds ratios (OR) and their 95% confidence intervals (95% CI). There were 253 cases and 759 controls. The reduction in risk of esophageal cancer mortality in individuals who had ever attended screening was 47% (OR: 0.53, 95% CI: 0.37–0.77). Compared with never-screened subjects, the ORs for screened subjects within 36 and 48 months before the reference date were 0.59(0.39–0.89) and 0.59(0.40–0.87); the ORs for 50–59 year old subjects were 0.48(0.28–0.85). The results suggest a 47% reduction in esophageal cancer mortality risk due to endoscopic screening, which may have significant implications for esophageal cancer screening in China, especially in rural areas.

A community-based, case-control study evaluating mortality reduction from gastric cancer by endoscopic screening in Japan

Aims

Although the incidence of gastric cancer has decreased in the last 3 decades, it remains the second leading cause of cancer death worldwide. In Asian countries, the burden of gastric cancer has remained, and cancer screening is normally expected to reduce gastric cancer death. We conducted a community-based, case-control study to evaluate the reduction of mortality from gastric cancer by endoscopic screening.

Methods

Case subjects were defined as individuals who had died of gastric cancer between 2003 and 2006 in 4 cities in Tottori Prefecture, and between 2006 and 2010 in Niigata City, Japan. Up to 6 control subjects were matched by sex, birth year (±3 years), and the residence of each corresponding case subject from the population lists in the study areas. Control subjects were required to be disease-free at the time when the corresponding case subjects were diagnosed as having gastric cancer. The odds ratios (ORs) were calculated for those who had participated in endoscopic or radiographic screening before the reference date when the case subjects were diagnosed as having gastric cancer, compared with subjects who had never participated in any screening. Conditional logistic-regression models for matched sets were used to estimate the ORs and 95% confidence intervals (CIs).

Results

The case subjects consisted of 288 men and 122 women for case subjects, with 2,292 matched control subjects. Compared with those who had never been screened before the date of diagnosis of gastric cancer in the case subjects, the ORs within 36 months from the date of diagnosis were 0.695 (95% CI: 0.489–0.986) for endoscopic screening and 0.865 (95% CI : 0.631–1.185) for radiographic screening.

Conclusions

The results suggest a 30% reduction in gastric cancer mortality by endoscopic screening compared with no screening within 36 months before the date of diagnosis of gastric cancer.

Prostate-specific antigen and prostate cancer mortality: a systematic review

CONTEXT

Although findings from recently published clinical trials and a review from the U.S. Preventive Services Task Force suggest that there is limited to no prostate cancer mortality benefit associated with prostate-specific antigen (PSA) screening, confusion remains as to whether the use of PSA as a screening tool for prostate cancer is warranted.

EVIDENCE ACQUISITION

A systematic literature review was done in 2012 to identify case-control studies from the past 20 years that focused on evaluating the association between screening for prostate cancer and prostate cancer mortality. Emphasis was put on synthesizing the results of these studies, evaluating their limitations, and identifying remaining questions and issues that should be addressed in future studies.

EVIDENCE SYNTHESIS

A total of seven studies were identified in this time period, with the majority suggesting that a reduction in prostate cancer mortality is associated with PSA screening. However, the findings may be limited by various biases inherent to case-control studies of screening tests, such as selection biases resulting from both case and control subject selection, exposure measurement issues, lead and length biases, and issues specific to prostate cancer screening such as the influence of digital rectal examinations.

CONCLUSIONS

Findings from existing case-control studies of PSA and prostate cancer mortality suggest that there is a mortality benefit from PSA screening. However, these studies may be limited by bias and must therefore be interpreted with caution. As uncertainty regarding PSA screening remains, future studies to evaluate the association between PSA and prostate cancer mortality should address these potential biases directly.

Quantifying lead-time bias in risk factor studies of cancer through simulation

PURPOSE

Lead-time is inherent in early detection and creates bias in observational studies of screening efficacy, but its potential to bias effect estimates in risk factor studies is not always recognized. We describe a form of this bias that conventional analyses cannot address and develop a model to quantify it.

METHODS

Surveillance Epidemiology and End Results (SEER) data form the basis for estimates of age-specific preclinical incidence, and log-normal distributions describe the preclinical duration distribution. Simulations assume a joint null hypothesis of no effect of either the risk factor or screening on the preclinical incidence of cancer, and then quantify the bias as the risk-factor odds ratio (OR) from this null study. This bias can be used as a factor to adjust observed OR in the actual study.

RESULTS

For this particular study design, as average preclinical duration increased, the bias in the total-physical activity OR monotonically increased from 1% to 22% above the null, but the smoking OR monotonically decreased from 1% above the null to 5% below the null.

CONCLUSIONS

The finding of nontrivial bias in fixed risk-factor effect estimates demonstrates the importance of quantitatively evaluating it in susceptible studies.

Breast cancer screening: evidence of benefit depends on the method used

In this article, we discuss the most common epidemiological methods used for evaluating the ability of mammography screening to decrease the risk of breast cancer death in general populations (effectiveness). Case-control studies usually find substantial effectiveness. However when breast cancer mortality decreases for reasons unrelated to screening, the case-control design may attribute to screening mortality reductions due to other causes. Studies based on incidence-based mortality have obtained contrasted results compatible with modest to considerable effectiveness, probably because of differences in study design and statistical analysis. In areas where screening has been widespread for a long time, the incidence of advanced breast cancer should be decreasing, which in turn would translate into reduced mortality. However, no or modest declines in the incidence of advanced breast cancer has been observed in these areas. Breast cancer mortality should decrease more rapidly in areas with early introduction of screening than in areas with late introduction of screening. Nonetheless, no difference in breast mortality trends has been observed between areas with early or late screening start. When effectiveness is assessed using incidence-based mortality studies, or the monitoring of advanced cancer incidence, or trends in mortality, the ecological bias is an inherent limitation that is not easy to control. Minimization of this bias requires data over long periods of time, careful selection of populations being compared and availability of data on major confounding factors. If case-control studies seem apparently more adequate for evaluating screening effectiveness, this design has its own limitations and results must be viewed with caution.See related Opinion article: http://www.biomedcentral.com/1741-7015/10/106 and Commentary http://www.biomedcentral.com/1741-7015/10/164.

Breast cancer screening: are we seeing the benefit?

A decline in breast cancer mortality has been observed in western European Countries since the middle of the 1990s. Different methodological approaches, including case-control studies, incidence-based mortality studies, and trend studies, have been used to assess the effectiveness of mammography screening programmes in reducing breast cancer mortality. However, not all methods succeed in distinguishing the relative contributions of service screening and taking correctly into consideration the potential source of bias that might affect the estimate. Recently, a review of six case-control studies confirmed a breast cancer mortality reduction ranging from 38% to 70% among screened women. This figure is in accordance with the estimate obtained from incidence-based mortality studies if screening compliance is taken into account. We will describe the methodological constraints of mortality trend studies in predicting the impact of screening on mortality and the necessary caution that must be applied when interpreting the results of such studies. In conclusion, when appropriate methodological approaches are used, it is evident that mammographic screening programmes have contributed substantially to the observed decline in breast cancer mortality.

Minor influence of self-selection bias on the effectiveness of breast cancer screening in case-control studies in the Netherlands

Background

Self-selection bias is considered to be a problem when evaluating the effectiveness of breast cancer service screening in case-control studies.

Objective

Using the incidence-based mortality method (IBM), a correction factor for the potential influence of self-selection can be derived from a group of non-screened women and a group of not-invited women.

Methods

Breast cancer patients, diagnosed in 1990–1995 and between the ages of 50 to 70, were selected from the Netherlands Cancer Registry and five screening regions in the Netherlands. Person-years were calculated for non-screened and not-invited women by using population data available on the number of women invited, the number of women screened and the total population. Incidence-based breast cancer mortality rates according to screening status were calculated for the five screening regions.

Results

Between 1990–1995, 15,541 patients were diagnosed with breast cancer. An analysis of ten-year follow-up after diagnosis resulted in 3903 breast cancer deaths, of which 2631 were not-invited and 345 were non-screened. Poisson regression analysis showed heterogeneity between the regions with a range of IBM ratios from 0.64 (95% CI: 0.46–0.90) to 1.08 (95% CI: 0.82–1.43).

Conclusions

Heterogeneity between the regions stresses the importance of a country- and/or region-specific estimate of self-selection. Adjusting for self-selection bias in the regional case-control studies would not change the breast cancer mortality reduction in three regions and would result in an even larger effect in two regions. Looking at the range of IBM ratios the overall influence of self-selection in the Netherlands is minor.

Normative data for the EORTC QLQ-C30 and EORTC-sexuality items in the general Dutch population

AIM

The aim of the present study was to generate Dutch reference data for the EORTC QLQ-C30 and for five sexuality items from the EORTC QL-item bank. Furthermore, to evaluate the relative impact of self-reported health problems on these outcomes and compare the Dutch normative EORTC QLQ-C30 overall QoL with available Scandinavian and German normative data.

METHODS

QLQ-C30 and sexual item normative data were obtained from the Health and Health Complaints project from CentERdata. The CentERpanel is an online household panel consisting of more than 2000 Dutch households, representative of the Dutch-speaking population in the Netherlands.

RESULTS

The questionnaire was completed by 1731 (78%) CentERpanel members. For both men and women, functional health (except emotional functioning) decreased with age, and the symptoms pain and fatigue increased with age. Men scored statistically but never clinically significantly better on most functional scales than women. Men reported higher levels of sexual interest and activity than women. All subgroups of participants with health problems reported lower physical and role functioning and overall quality of life (QoL). Those with depression (n=79) reported functioning scores 20-30 points lower than participants without any condition. Dutch men and women reported high levels of overall QoL as compared to previously published Scandinavian and German normative data.

CONCLUSION

Age, gender and other health problems are important when comparing QoL and sexuality among different cancer cohorts. Normative data on QoL and sexuality are needed to interpret QoL issues among the growing group of (long-term) cancer survivors.

Organizational and clinical implications of integrating an alcohol screening and brief intervention within non-substance abuse serving agencies

Although there have been efforts to advance evidenced-based practices into community-based organizations the limited successes of dissemination and poor implementation of efficacious treatments within these organizations are beginning to be documented. This article builds on the knowledge gained from organizational research and those internal structures (e.g., culture and climate), which possibly impede or enhance evidenced-based practice implementation within community-based organizations. While there are many evidenced-based practices available to human services organizations, there seems to be a gap between research and the implementation of these clinical practices. Recommendations are provided to better enable community-based organizations to integrate evidenced-based practice into its existing service structures.

A remarkable reduction of breast cancer deaths in screened versus unscreened women: a case-referent study

OBJECTIVE

We designed a case-referent study to investigate the effect of mammographic screening at the individual level, looking at the association of breast cancer death with screening history.

METHODS

The study population included all women aged 50-75 in the province of Limburg, the Netherlands who had been invited to the screening program from 1989 to 2006. From this population, 118 cases originated who died of breast cancer in 2004 or 2005. The screening history of these cases was collected and compared with a sample of the invited population. The breast cancer death rate in the screened relative to the unscreened women was estimated as the odds ratio (OR). This OR was adjusted for self-selection bias, the difference in baseline risk for breast cancer death between screened and unscreened women.

RESULTS

Analysis of the data showed a breast cancer mortality reduction of 70% in the screened versus the unscreened women (OR = 0.30, 95% CI 0.14-0.63). The magnitude of self-selection was estimated specifically for Limburg. After correction for self-selection bias, the effect of screening increased to 76% (OR = 0.24, 95% CI 0.10-0.58).

CONCLUSION

Screening resulted in a remarkable reduction in breast cancer mortality. Contrary to findings in other countries, adjustment for self-selection in Limburg had no influence on the impact of screening. Thanks to a well-organized centralized screening program, similar results are expected in other regions of the Netherlands.

Evaluation of cancer service screening: case referent studies recommended

Various cancer screening trials, randomised or otherwise controlled, have demonstrated reductions in cancer mortality. As a consequence, population screening programmes have been implemented. In the mean time, major advances are being made in early detection and treatment modalities of specific cancers and pre-cancers. The impact of these improvements should have bearing on the beneficial effect of periodical screening in preventing cancer death. To monitor these dynamics in the effectiveness of screening, case-referent studies are designed. The effectiveness is estimated by calculating an odds ratio indicating the cancer death rate in screened versus not screened invitees. The major criticisms of case referent studies are potential selection bias and confounding bias of the odds ratio. By properly designing and applying sensitivity analyses these biases can be minimised.

Screening for bladder cancer: theoretical and practical issues in considering the treated and untreated natural history of the various forms of the disease

Screening is used to detect disease earlier in its course, allow earlier treatment, and presumably decrease morbidities and potential mortality associated with the later expression of more advanced disease and presumably more complex treatments consequently required. Judicious screening in bladder cancer depends on an understanding of how the different forms of bladder cancer express their biological potential, whether the tools available for screening have sufficient sensitivity and specificity to have accurate predictive value in accurately diagnosing and assessing each cancer diathesis earlier in its course, and how this may influence the morbidities and mortality associated with each. The principles of screening, potential biases that can affect their accuracy and the interpretation of outcomes, tools currently available for screening, their efficacies and pitfalls, and lessons learned from studies of the role of screening in prostate cancer will be reviewed to offer an understanding of the potential role that screening may play in the different forms of bladder cancer in the context of their preclinical and treated natural history.

Erectile dysfunction and mental health in a general population of older men

INTRODUCTION

Erectile dysfunction (ED) is more prevalent with increasing age. Previous studies showed that ED was negatively associated with mental health (MH) in specific patient groups.

AIM

To examine the association, and potential mediating factors, between ED and MH in healthy elderly men.

MAIN OUTCOME MEASURES

ED was defined as (almost) always having problems in achieving or maintaining an erection if desired, or not being sexually active because of erectile problems. MH was assessed with 36-item Short-Form Health Survey scale MH5 with five items on, e.g., being happy or depressed (range 0-100). Potential mediators between ED and MH were satisfaction with and importance attached to sex life.

METHODS

The study population consisted of a consecutive sample of 3,810 participants from the European Randomized Study of Screening for Prostate Cancer, aged 57-78 years, who had screened negatively for prostate cancer. Associations between ED, potential mediating factors, and MH were tested by analysis of variance and analysis of covariance.

RESULTS

Covariance analysis, adjusted for age, comorbidity, and use of erectile aids, showed that men with ED had significantly lower MH scores (80.8 +/- 1.2) than men without ED (83.7 +/- 1.2; P < 0.001). ED was also associated with the potential mediator "satisfaction with sex life" but not with "importance attached to sex life." Men with ED were significantly more often dissatisfied with their sex lives (P < 0.001). Adjustment for satisfaction with sex life, but not for importance attached to sex life, reduced the strength of the association (beta value) between ED and poor MH from 2.88 to -0.84.

CONCLUSIONS

ED was associated with poorer MH. Satisfaction with sex life, but not importance attached to sex life, may play a mediating role in this association. These results suggest that if men with ED can be helped to be satisfied with their sex lives despite ED, MH can be preserved.

Lower risk of death from gastric cancer among participants of gastric cancer screening in Japan: a population-based cohort study

OBJECTIVE

This study aimed to investigate the association between gastric cancer screening and mortality from gastric cancer.

METHODS

In 1990, 47,605 Japanese subjects were recruited and completed a questionnaire about participation in gastric cancer screening and life-style. We followed up their vital status through December 2001. In this cohort, 41,394 subjects without a history of cancer were allocated to the screened group or the unscreened group according to their response to the question about gastric cancer screening. We estimated the relative risk (RR) of death from gastric cancer, death from any cause except gastric cancer, and incidence of gastric cancer with adjustment for potential confounding variables.

RESULTS

The risk of death from gastric cancer among the screened group was significantly lower than that among the unscreened group. The multivariate RR of death from gastric cancer for screened individuals compared with those not screened was 0.54 (95% confidence interval [CI]: 0.38, 0.77). The RR of death from any cause except gastric cancer was 0.83 (95% CI: 0.77, 0.90), and the RR of incidence of gastric cancer was 0.94 (95% CI: 0.79, 1.13).

CONCLUSION

Our data suggest that gastric cancer screening or factors associated with it may be associated with lower mortality from gastric cancer.

Evaluating markers for the early detection of cancer: overview of study designs and methods

BACKGROUND

The field of cancer biomarker development has been evolving rapidly. New developments both in the biologic and statistical realms are providing increasing opportunities for evaluation of markers for both early detection and diagnosis of cancer.

PURPOSE

To review the major conceptual and methodological issues in cancer biomarker evaluation, with an emphasis on recent developments in statistical methods together with practical recommendations.

METHODS

We organized this review by type of study: preliminary performance, retrospective performance, prospective performance and cancer screening evaluation.

RESULTS

For each type of study, we discuss methodologic issues, provide examples and discuss strengths and limitations.

CONCLUSION

Preliminary performance studies are useful for quickly winnowing down the number of candidate markers; however their results may not apply to the ultimate target population, asymptomatic subjects. If stored specimens from cohort studies with clinical cancer endpoints are available, retrospective studies provide a quick and valid way to evaluate performance of the markers or changes in the markers prior to the onset of clinical symptoms. Prospective studies have a restricted role because they require large sample sizes, and, if the endpoint is cancer on biopsy, there may be bias due to overdiagnosis. Cancer screening studies require very large sample sizes and long follow-up, but are necessary for evaluating the marker as a trigger of early intervention.

Joint National Cancer Institute-Food and Drug Administration Workshop on Research Strategies, Study Designs, and Statistical Approaches to Biomarker Validation for Cancer Diagnosis and Detection

Cancer remains the second leading cause of death in the United States, in spite of tremendous advances made in therapeutic and diagnostic strategies. Successful cancer treatment depends on improved methods to detect cancers at early stages when they can be treated more effectively. Biomarkers for early detection of cancer enable screening of asymptomatic populations and thus play a critical role in cancer diagnosis. However, the approaches for validating biomarkers have yet to be addressed clearly. In an effort to delineate the ambiguities related to biomarker validation and related statistical considerations, the National Cancer Institute, in collaboration with the Food and Drug Administration, conducted a workshop in July 2004 entitled "Research Strategies, Study Designs, and Statistical Approaches to Biomarker Validation for Cancer Diagnosis and Detection." The main objective of this workshop was to review basic considerations underpinning the study designs, statistical methodologies, and novel approaches necessary to rapidly advance the clinical application of cancer biomarkers. The current commentary describes various aspects of statistical considerations and study designs for cancer biomarker validation discussed in this workshop.

SCREENING WITH PROSTATE SPECIFIC ANTIGEN AND METASTATIC PROSTATE CANCER RISK: A POPULATION BASED CASE-CONTROL STUDY

PURPOSE

Screening of asymptomatic men with prostate specific antigen (PSA) remains a controversial issue. There is limited evidence that screening is effective in reducing mortality from prostate cancer. In the current study we determined if screening with PSA reduces the risk of metastatic prostate cancer.

MATERIALS AND METHODS

We conducted a population based case-control study among the residents of Metropolitan Toronto and 5 surrounding counties in Ontario, Canada. Data were obtained from 236 cases of metastatic prostate cancer and 462 controls randomly sampled from the source population and frequency matched to cases for age and area of residence. History of PSA testing, digital rectal examination, symptoms and other data were obtained from medical records and a self-administered questionnaire. The association between PSA screening and metastatic prostate cancer was measured by the Mantel-Haenszel odds ratio stratified by exposure observation time and other potential confounding factors.

RESULTS

In asymptomatic men, the frequency of PSA screening as determined from medical records was significantly lower among the cases compared with the controls (odds ratio 0.65, 95% confidence interval 0.45 to 0.93). The odds ratio was 0.52 (0.28 to 0.98) in men 45 to 59 years old and 0.67 (0.41 to 1.09) in those 60 to 84 years old.

CONCLUSIONS

In this case-control study screening of asymptomatic men with PSA was associated with a significantly reduced risk of metastatic prostate cancer. The results need to be confirmed in randomized controlled trials.

The efficacy of lung cancer screening conducted in 1990s: four case-control studies in Japan

The efficacy of lung cancer screening is still controversial. In order to evaluate efficacy of mass screening for lung cancer in 1990s, the Japanese Ministry of Health and Welfare planned to conduct four independent case-control studies in four different regions; Miyagi, Gunma, Niigata, and Okayama Prefecture. The study design of all the four studies was a matched case-control study in which the decedents from lung cancer were defined as cases. In Gunma Prefecture, a screening examination is annual miniature chest X-ray only, whereas sputum cytology is added for high-risk screenees in others. Matching conditions were gender, year of birth, smoking histories (except Okayama), and municipality. Smoking adjusted odds ratio (OR) of dying from lung cancer for those screened within 12 months before case diagnosis compared with those not screened ranged 0.40-0.68. Three of four studies revealed statistically significant reduction of the risk for lung cancer death. OR of pooled analysis, where all sets were combined and analyzed, was 0.56 (95% confidence interval: 0.48-0.65). Recent mass screening program for lung cancer in Japan could reduce the risk for lung cancer death. However, the possibility exists that some confounding factors affected the results. In order to elucidate whether the results can be applied to Western countries, further studies will be required.

Long-term efficacy of sigmoidoscopy in the reduction of colorectal cancer incidence

Screening sigmoidoscopy is associated with a reduction in both the incidence and mortality of colorectal cancer. Although current guidelines recommend sigmoidoscopy screening every 5 years, the duration of risk reduction is not known. We conducted a population-based case-control study to examine the association between sigmoidoscopy screening and colorectal cancer incidence. We collected information on screening history and risk factors from case patients with distal (n = 1026) and proximal (n = 642) colorectal cancer and from 1294 control subjects from October 1998 through February 2002. Screening sigmoidoscopy was associated with a statistically significant reduction in the incidence of distal colorectal cancer (odds ratio [OR] = 0.24, 95% confidence interval [CI] = 0.17 to 0.33). These reductions were sustained for up to 16 years with little attenuation. We also observed strong inverse associations between cancer incidence and sigmoidoscopy in analyses that included subjects with symptom-related tests. Current recommendations regarding the frequency of sigmoidoscopy screening may be unnecessarily aggressive.

The case for early detection

Early detection represents one of the most promising approaches to reducing the growing cancer burden. It already has a key role in the management of cervical and breast cancer, and is likely to become more important in the control of colorectal, prostate and lung cancer. Early-detection research has recently been revitalized by the advent of novel molecular technologies that can identify cellular changes at the level of the genome or proteome, but how can we harness these new technologies to develop effective and practical screening tests?

Using observational data to estimate an upper bound on the reduction in cancer mortality due to periodic screening

BACKGROUND

Because randomized cancer screening trials are very expensive, observational cancer screening studies can play an important role in the early phases of screening evaluation. Periodic screening evaluation (PSE) is a methodology for estimating the reduction in population cancer mortality from data on subjects who receive regularly scheduled screens. Although PSE does not require assumptions about natural history of cancer it requires other assumptions, particularly progressive detection - the assumption that once a cancer is detected by a screening test, it will always be detected by the screening test.

METHODS

We formulate a simple version of PSE and show that it leads to an upper bound on screening efficacy if the progressive detection assumption does not hold (and any effect of birth cohort is minimal) To determine if the upper bound is reasonable, for three randomized screening trials, we compared PSE estimates based only on screened subjects with PSE estimates based on all subjects.

RESULTS

In the three randomized screening trials, PSE estimates based on screened subjects gave fairly close results to PSE estimates based on all subjects.

CONCLUSION

PSE has promise for obtaining an upper bound on the reduction in population cancer mortality rates based on observational screening data. If the upper bound estimate is found to be small and any birth cohort effects are likely minimal, then a definitive randomized trial would not be warranted.

Statistical issues in randomized trials of cancer screening

BACKGROUND

The evaluation of randomized trials for cancer screening involves special statistical considerations not found in therapeutic trials. Although some of these issues have been discussed previously, we present important recent and new methodologies.

METHODS

Our emphasis is on simple approaches.

RESULTS

We make the following recommendations: (1) Use death from cancer as the primary endpoint, but review death records carefully and report all causes of death; (2) Use a simple "causal" estimate to adjust for nonattendance and contamination occurring immediately after randomization; (3) Use a simple adaptive estimate to adjust for dilution in follow-up after the last screen

CONCLUSION

The proposed guidelines combine recent methodological work on screening endpoints and noncompliance/contamination with a new adaptive method to adjust for dilution in a study where follow-up continues after the last screen. These guidelines ensure good practice in the design and analysis of randomized trials of cancer screening.

A case-control study of lung cancer screening in Okayama Prefecture, Japan

The effectiveness of lung cancer screening in reducing mortality still remains uncertain. In order to evaluate the efficacy of lung cancer screening, a case-control study was conducted in Okayama Prefecture, Japan. The study area consisted of 34 municipalities where a population-based lung cancer screening had been conducted. Chest X-ray examinations for all participants and sputum cytology for high-risk participants were offered annually. The cases analyzed in this study consisted of 412 individuals aged between 40 and 79 who died of lung cancer. A total of 3490 controls, two to ten for each case matched by gender, year of birth, and living district were randomly collected. Screening histories of cases were compared with those of and matched controls for the identical calendar period prio to diagnosis of the case. Smoking adjusted odds ratio (OR) of death from lung cancer for screened individuals versus unscreened, within 12 months before diagnosis, was calculated as 0.59 (95% confidence interval: 0.46-0.74; P=0.0001). The OR for women (0.39, 95% confidence interval: 0.24-0.64) was lower than that for men (0.67, 95% confidence interval: 0.51-0.87), although both were statistically significant. These results suggest that lung cancer screening contributes to reducing lung cancer mortality by 41%.

An evaluation of screening for lung cancer in Niigata Prefecture, Japan: a population-based case-control study

Although an annual screening programme for lung cancer has been carried out widely in Japan since 1987, there is insufficient evidence to confirm its efficacy in terms of reducing mortality. In order to evaluate the efficacy of the lung cancer screening which has been widely carried out in Japan since 1987, a case-control study was conducted in Niigata Prefecture, Japan. In the study area, chest X-ray examinations for all participants and sputum cytology for high-risk participants were offered annually. Case subjects, who had died from lung cancer (174), and control subjects matched by sex, year of birth, residence and smoking status (801), who had been alive at the time of diagnosis of the corresponding case, were selected from the National Health Insurance holders. Screening histories of the subjects were compared between cases and matched controls for the identical calendar period before the time of diagnosis of the cases. The odds ratio of death from lung cancer for those screened within 12 months vs those not screened was 0.401 (95% CI: 0.272-0.591) with adjustment by smoking index. Our results suggest that annual lung cancer screening might reduce mortality from lung cancer by approximately 60%.

A case-control study for evaluating the efficacy of mass screening program for lung cancer in Miyagi Prefecture, Japan

BACKGROUND

In Miyagi Prefecture, Japan, a mass screening program for lung cancer has been conducted since 1982 (miniature chest X-ray for all screenees and sputum cytology for those with a smoking index > or = 600) [smoking index 600 = 30 pack years, the average number of cigarettes smoked per day multiplied by the number of years of regular smoking]. Over 1500 lung carcinomas, including 250 roentgenographically occult lung tumors, were detected and treated up to 1999. In the current study, a nested case-control study was conducted in the population that was screened in 1989 to evaluate the efficacy of the screening program for lung cancer.

METHODS

To reduce self-selection bias, the source population was defined as screenees with negative results in 1989 (284,226 individuals). In the population, 474 individuals died of lung carcinoma during 1992-1994. After exclusion, 328 patients who died of primary lung carcinoma at between ages 40 years and 79 years were defined as the cases. Six controls were supposed to be selected in the source population for each case and matched by gender, year of birth, municipality, and smoking habits. Controls who had died or moved before the matched case was diagnosed were excluded. Finally, 328 cases and 1886 controls were selected. Screening histories were compared, and odds ratios were calculated using conditional logistic regression analysis.

RESULTS

Within the 12 months before diagnosis, 241 of 328 cases (73.5%) had attended the screening compared with 1557 of 1886 controls (82.6%). The smoking-adjusted odds ratio was 0.54 (95% confidence interval, 0.41-0.73).

CONCLUSIONS

The mass screening program for lung cancer in Miyagi Prefecture was capable of reducing by 46% the risk of death from carcinoma of the lung.

A novel form of ascertainment bias in case-control studies of cancer screening

In case-control studies of cancer screening, some have generally admonished investigators against case definitions based on diagnosis dates because of lead-time bias. However, perhaps partly due to vagueness, the admonitions have been frequently ignored. A recurrence-time model simulates case ascertainment when diagnosis must occur within a specific calendar period. The model depends on screening test sensitivity and rate, age-specific preclinical incidence rates, and preclinical duration time and survival time distributions. For one study of sigmoidoscopic screening for colorectal cancer, when the true odds ratio is 1, its estimate is 0.50 to 0.75 under plausible assumptions. This bias can affect any observational study wherein case definition depends on diagnosis times (e.g., health-plan enrollment data). To avoid bias in observational investigations of cancer screening wherein the case definition depends on the diagnosis date, one must ensure that both screening and preclinical incidence do not occur before the case definition period.

Reducing colorectal cancer mortality by repeated faecal occult blood test: a nested case-control study

Randomised trials have shown the efficacy of faecal occult blood testing (FOBT) in reducing colorectal cancer mortality, but observational studies are needed to monitor such efficacy in population programmes. We conducted a nested case-control study on a cohort of 21,879 subjects who participated in a colorectal screening programme from 1978 to 1995, undergoing at least one FOBT test. 95 fatal cases of colorectal cancer were eligible for the study. For each fatal case, 5 non-fatal matched controls were randomly selected from the cohort. FOBT screening history was less common among cases than controls. The odds ratio of colorectal cancer mortality among 'attenders' (defined as those who underwent a second FOBT within 2 years of study entry) with respect to 'non-attenders' was 0.64 (95% confidence interval 0.36-1.15). We also computed odds ratios defining exposure as one or more tests in the detectable preclinical period, hypothesising various lengths for the latter, which, however, yielded an efficacy estimate biased towards the null. A strong inverse relationship was observed between mortality and the number of tests, but this phenomenon is interpretable as 'healthy screenee bias'. The results suggest that the potential efficacy in preventing colorectal cancer mortality through annual FOBT screening may be of the order of one third.