Adverse Effects Of Screening Research Articles

Quality of life after screening for atrial fibrillation: a substudy from a randomised screening trial

Abstract Background Screening for atrial fibrillation (AF) is rising, yet trials have failed to show efficacy for stroke prevention from screening and subsequent anticoagulation. Quality of life is an important outcome for patients and physicians, however, it is largely unknown how this outcome is affected by screening for AF. The adverse effects of screening should be considered before implementing systematic screening. Purpose To explore changes in quality of life associated with screening for AF and subsequent anticoagulant treatment upon AF detection. Methods We used quality of life data from 6,004 persons with stroke risk factors randomised to usual care (n=4,503) or screening for AF using implantable loop recorder and anticoagulation for AF episodes lasting ≥6 minutes (n=1,501). The validated EQ-5D-5L tool evaluates health-related quality of life in five domains (mobility, selfcare, usual activities, pain/discomfort and anxiety/depression), rendering a final score in EQ-index (worst=-0.76 best=1.00) combined with an EQ-VAS score (worst=0, best=100). EQ-index and EQ-VAS were analysed with linear mixed models from baseline through year three. The domains were also analysed with logistic regression to report the risk of major problems (defined as a rating of 3, 4, or 5 in the range [1-5], where 1 corresponds to no problem and 5 corresponds to an extreme problem within a given domain) overall and separately. Sensitivity analyses with imputation for missing data were performed. Results Data were available for 5,162 (86.0%) participants at baseline and in year three, and 227 (5.0%) in usual care and 65 (4.3%) in the screened group had died before the last assessment. At baseline, 1,202 of 5,162 (23.3%) participants reported major pain/discomfort problems, and 666 of 5,162 (12.9%) reported major mobility problems (Figure 1). Major selfcare problems were the least frequent problem reported by 83 of 5,162 participants (1.6%). The occurrence of major problems was increased after 3 years in all domains and in both randomisation groups, with a 2% higher occurrence of major pain/discomfort in the control group compared to the screened group. At baseline, the average EQ-index was 0.88 (±0.16) and EQ-VAS 78.4 (±16.2). After three years, the EQ-index decreased by -0.05 (-0.05; -0.04), p<0.0001 in the control group vs. -0.04 (-0.05; -0.02) in the screened group and EQ-VAS with -6.06 (-6.54; -5.57) in the control group vs. -5.18 (-6.52; -3.78) in the screened group, resulting in no statistically significant difference between the groups (p=0.063 and p=0.056) (Figure 2). The screened group was equally likely to report at least one major problem in quality of life after three years (odds ratio 0.93 (0.77;1.13)), but was less likely to report major pain/discomfort (odds ratio 0.84 (0.72;0.98)), compared with the control group. Conclusion Systematic and intensive screening for atrial fibrillation did not improve quality of life compared to usual practice.

Avances hacia el cribado personalizado del cáncer de mama: el papel de la Atención Primaria

Breast cancer is the leading cause of death in the world among women. The Spanish National Health System (SNHS) introduced population-based breast cancer screening in 1990. As in most European programs, risk is identified on the basis of age and a mammogram is offered every two years to women aged 50–69 years. Scientific evidence is moving toward personalized screening, based on individual risk. This article presents the clinical trials that will evaluate the efficacy of personalized screening and some studies carried out in our environment on the effect of informing women of the benefits and adverse effects of screening or the acceptability and feasibility of offering personalized screening, in the Shared Decision Making context. The Preventive Activities and Health Promotion Program can help transform screening in our SNHS.

Cost-effectiveness and budget impact analysis of a population-based screening program for colorectal cancer

BackgroundColorectal cancer (CRC) is one of the leading causes of cancer mortality in Belgium. In Flanders (Belgium), a population-based screening program with a biennial immunochemical faecal occult blood test (iFOBT) in women and men aged 56–74 has been organised since 2013. This study assessed the cost-effectiveness and budget impact of the colorectal population-based screening program in Flanders (Belgium). MethodsA health economic model was conducted, consisting of a decision tree simulating the screening process and a Markov model, with a time horizon of 20years, simulating natural progression. Predicted mortality and incidence, total costs, and quality-adjusted life-years (QALYs) with and without the screening program were calculated in order to determine the incremental cost-effectiveness ratio of CRC screening. Deterministic and probabilistic sensitivity analyses were conducted, taking into account uncertainty of the model parameters. ResultsMortality and incidence were predicted to decrease over 20years. The colorectal screening program in Flanders is found to be cost-effective with an ICER of 1681/QALY (95% CI −1317 to 6601) in males and €4,484/QALY (95% CI −3254 to 18,163). The probability of being cost-effective given a threshold of €35,000/QALY was 100% and 97.3%, respectively. The budget impact analysis showed the extra cost for the health care payer to be limited. ConclusionThis health economic analysis has shown that despite the possible adverse effects of screening and the extra costs for the health care payer and the patient, the population-based screening program for CRC in Flanders is cost-effective and should therefore be maintained.

Mammography for Older Women?

Mammography for Older Women?

There are calls for a national screening programme for prostate cancer: what is the evidence to justify such a national screening programme?

Prostate cancer is the commonest cancer in men and a major health issue worldwide. Screening for early disease has been available for many years, but there is still no national screening programme established in the United Kingdom. To assess the latest evidence regarding prostate cancer screening and whether it meets the necessary requirements to be established as a national programme for all men. Electronic databases and library catalogues were searched electronically and manual retrieval was performed. Only primary research results were used for the analysis. In recent years, several important randomised controlled trials have produced varied outcomes. In Europe the largest study thus far concluded that screening reduced prostate cancer mortality by 20%. On the contrary, a large American trial found no reduction in mortality after 7-10 years follow-up. Most studies comment on the adverse effects of screening - principally those of overdiagnosis and subsequent overtreatment. Further information about the natural history of prostate cancer and accuracy of screening is needed before a screening programme can be truly justified. In the interim, doctors and patients should discuss the risks, benefits and sequelae of taking part in voluntary screening for prostate cancer.

Opening Pandora's box: The experiences of having an asymptomatic aortic aneurysm under surveillance

Abdominal aortic aneurysm (AAA) is a ballooning-out of the aorta that does not normally give any symptoms. Undetected and untreated an aortic aneurysm can rupture, which in most cases is fatal. Mass screening of 65-year old men for the early detection of AAA and, in selected cases, operation seem to reduce mortality due to rupture, although, screening has not reduced the overall mortality in this group. In Västra Götaland, the southwest part of Sweden, screening for AAA amongst 65-year old men started in 2009. There are controversies within the medical community about the benefits and adverse effects of screening. In order to explore men's experiences of being screened and knowing they had an aortic aneurysm, we undertook a qualitative interview study with 15 men who in the screening programme were identified as having an aortic aneurysm and who were to be followed-up with annual ultrasonic examinations for an indeterminate number of years. The interviews were analysed for categories and themes using content analysis. The study found that the men were ambivalent about the knowledge that they had an AAA and about the follow-up monitoring. They appreciated having the knowledge but it was accompanied by worry, feelings of anxiety and existential thoughts about the fragility and finiteness of life. We recommend that before a screening programme is implemented, the psycho-social consequences should be thoroughly investigated. Participants should be given adequate and understandable information about the consequences of screening so that they can make an informed choice whether to participate or not.

False-positive results from colorectal cancer screening in Catalonia (Spain), 2000–2010

To identify factors associated with a false-positive result in a population-based colorectal cancer (CRC) screening programme with the faecal occult blood test (FOBT) in Catalonia between 2000 and 2010. The study population consisted of participants of the Catalan CRC screening programme with a positive FOBT who underwent a colonoscopy for diagnostic confirmation from 2000 to 2010. A false-positive result was defined as having a positive test but detecting no high-risk adenoma or cancer in the follow-up colonoscopy. Multivariate logistic regression models were performed to identify sociodemographic and screening variables related to false-positive results. Adjusted odds ratios (OR) and their 95% confidence intervals (CI) were estimated. Over the screening period, 1074 (1.7%) of the 63,332 screening tests had a positive result in the Catalan CRC screening programme. The false-positive proportion was 55.2% (n = 546). Women were more likely to have a positive FOBT in the absence of CRC neoplasia than men (adjusted OR = 2.91; 95% CI: 2.22-3.28). During the first prevalence round, the proportion of false-positive results was higher than in subsequent rounds (69.5% vs. 48.9%; P < 0.05). Re-screening and having a bleeding pathology such as haemorrhoids or anal fissures were also associated with a false-positive result. The proportion of false-positive results and the associated risks should be estimated to provide an eligible population with more reliable information on the adverse effects of screening.

E4. Current issues in breast cancer screening

E4. Current issues in breast cancer screening

Effectiveness of screening preschool children for amblyopia: a systematic review.

BackgroundAmblyopia and amblyogenic factors like strabismus and refractive errors are the most common vision disorders in children. Although different studies suggest that preschool vision screening is associated with a reduced prevalence rate of amblyopia, the value of these programmes is the subject of a continuing scientific and health policy discussion. Therefore, this systematic review focuses on the question of whether screening for amblyopia in children up to the age of six years leads to better vision outcomes.MethodsTen bibliographic databases were searched for randomised controlled trials, non-randomised controlled trials and cohort studies with no limitations to a specific year of publication and language. The searches were supplemented by handsearching the bibliographies of included studies and reviews to identify articles not captured through our main search strategy.ResultsFive studies met the inclusion criteria. Of these, three studies suggested that screening is associated with an absolute reduction in the prevalence of amblyopia between 0.9% and 1.6% (relative reduction: between 45% and 62%). However, the studies showed weaknesses, limiting the validity and reliability of their findings. The main limitation was that studies with significant results considered only a proportion of the originally recruited children in their analysis. On the other hand, retrospective sample size calculation indicated that the power based on the cohort size was not sufficient to detect small changes between the groups. Outcome parameters such as quality of life or adverse effects of screening have not been adequately investigated in the literature currently available.ConclusionPopulation based preschool vision screening programmes cannot be sufficiently assessed by the literature currently available. However, it is most likely that the present systematic review contains the most detailed description of the main limitations in current available literature evaluating these programmes. Therefore, future research work should be guided by the findings of this publication.

Universal Newborn Hearing Screening: Systematic Review to Update the 2001 US Preventive Services Task Force Recommendation

This review is an update for the US Preventive Services Task Force on universal newborn hearing screening to detect moderate-to-severe permanent, bilateral congenital hearing loss. We focus on 3 key questions: (1) Among infants identified by universal screening who would not be identified by targeted screening, does initiating treatment before 6 months of age improve language and communication outcomes? (2) Compared with targeted screening, does universal screening increase the chance that treatment will be initiated by 6 months of age for infants at average risk or for those at high risk? (3) What are the adverse effects of screening and early treatment? Medline and Cochrane databases were searched to identify articles published since the 2002 recommendation. Data from studies that met inclusion criteria were abstracted, and studies were rated for quality with predetermined criteria. A good-quality retrospective study of children with hearing loss indicates that those who had early versus late confirmation and those who had undergone universal newborn screening versus none had better receptive language at 8 years of age but not better expressive language or speech. A good-quality nonrandomized trial of a large birth cohort indicates that infants identified with hearing loss through universal newborn screening have earlier referral, diagnosis, and treatment than those not screened. These findings are corroborated by multiple descriptive studies of ages of referral, diagnosis, and treatment. Usual parental reactions to an initial nonpass on a hearing screen include worry, questioning, and distress that resolve for most parents. Cochlear implants have been associated with higher risks for bacterial meningitis in young children. Children with hearing loss who had universal newborn hearing screening have better language outcomes at school age than those not screened. Infants identified with hearing loss through universal screening have significantly earlier referral, diagnosis, and treatment than those identified in other ways.

The undesirable psychological adverse effects of screening

The psychological adverse effects might play an important role in the non-compliance with the offered screening examination. The possible sources of them are three-fold: 1. The general human attitude, such as the rejection of health interventions, particularly those aiming at the prevention of eventual future health problems instead of handling existing complaints and symptoms at present; the screening can be seen as a "future-oriented" intervention. 2. The cultural image of cancer and the disbelief of its curability. 3. The subjective experiences in relation to the screening process. The providers have to do their best to eliminate these causes: by means of a) health education addressing people of various ages, social classes and cultural levels, promoting the understanding of the importance of disease prevention, and, changing their negative, defeatist attitude towards cancer; b) minimizing the psychological adverse effects of all kinds. This can be done by proper organisation of the screening process; optimizing the quality of work, and, provision of good quality of information and advice to the screenees before, during and after the screening.

Screening for Elevated Lead Levels in Childhood and Pregnancy: An Updated Summary of Evidence for the US Preventive Services Task Force

In 1996, the US Preventive Services Task Force provided recommendations for routine screening of asymptomatic children and pregnant women for elevated blood lead levels. This review updates the evidence for the benefits and harms of screening and intervention for elevated blood lead in asymptomatic children and pregnant women. We searched Medline, reference lists of review articles, and tables of contents of leading pediatric journals for studies published in 1995 or later that contained new information about the prevalence, diagnosis, natural course, or treatment of elevated lead levels in asymptomatic children aged 1 to 5 years and pregnant women. The prevalence of elevated blood lead levels among children and women in the United States, like that in the general population, continues to decline sharply, primarily because of marked reductions in environmental exposure, but still varies substantially among different communities and populations. Similar to the findings in 1996, our searches did not identify direct evidence from controlled studies that screening children for elevated blood lead levels results in improved health outcomes, and there was no direct evidence identified from controlled studies that screening improves pregnancy or perinatal outcomes. No new relevant information regarding the accuracy of screening for lead toxicity was identified during the update, and we did not identify evidence that demonstrates that universal screening for blood lead results in better clinical outcomes than targeted screening. Substantial new relevant information regarding the adverse effects of screening and interventions was not identified. There is no persuasive evidence that screening for elevated lead levels in asymptomatic children will improve clinical outcomes. For those children who are screened and found to have elevated levels, there is conflicting evidence demonstrating the clinical effectiveness of early detection and intervention.

Screening for Speech and Language Delay in Preschool Children: Systematic Evidence Review for the US Preventive Services Task Force

PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275). Published in the public domain by the American Academy of Pediatrics. Speech and language development is a useful indicator of a child's overall development and cognitive ability and is related to school success. Identification of children at risk for developmental delay or related problems may lead to intervention services and family assistance at a young age, when the chances for improvement are best. However, optimal methods for screening for speech and language delay have not been identified, and screening is practiced inconsistently in primary care. We sought to evaluate the strengths and limits of evidence about the effectiveness of screening and interventions for speech and language delay in preschool-aged children to determine the balance of benefits and adverse effects of routine screening in primary care for the development of guidelines by the US Preventive Services Task Force. The target population includes all children up to 5 years old without previously known conditions associated with speech and language delay, such as hearing and neurologic impairments. Studies were identified from Medline, PsycINFO, and CINAHL databases (1966 to November 19, 2004), systematic reviews, reference lists, and experts. The evidence review included only English-language, published articles that are available through libraries. Only randomized, controlled trials were considered for examining the effectiveness of interventions. Outcome measures were considered if they were obtained at any time or age after screening and/or intervention as long as the initial assessment occurred while the child was < or =5 years old. Outcomes included speech and language measures and other functional and health outcomes such as social behavior. A total of 745 full-text articles met our eligibility criteria and were reviewed. Data were extracted from each included study, summarized descriptively, and rated for quality by using criteria specific to different study designs developed by the US Preventive Services Task Force. The use of risk factors for selective screening has not been evaluated, and a list of specific risk factors to guide primary care physicians has not been developed or tested. Sixteen studies about potential risk factors for speech and language delay in children enrolled heterogeneous populations, had dissimilar inclusion and exclusion criteria, and measured different risk factors and outcomes. The most consistently reported risk factors included a family history of speech and language delay, male gender, and perinatal factors. Other risk factors reported less consistently included educational levels of the mother and father, childhood illnesses, birth order, and family size. The performance characteristics of evaluation techniques that take < or =10 minutes to administer were described in 24 studies relevant to screening. Studies that were rated good to fair quality reported wide ranges of sensitivity and specificity when compared with reference standards (sensitivity: 17-100%; specificity: 45-100%). Most of the evaluations, however, were not designed for screening purposes, the instruments measured different domains, and the study populations and settings were often outside of primary care. No "gold standard" has been developed and tested for screening, reference standards varied across studies, few studies compared the performance of > or =2 screening techniques in 1 population, and comparisons of a single screening technique across different populations are lacking. Fourteen good- and fair-quality randomized, controlled trials of interventions reported significantly improved speech and language outcomes compared with control groups. Improvement was demonstrated in several domains including articulation, phonology, expressive language, receptive language, lexical acquisition, and syntax among children in all age groups studied and across multiple therapeutic settings. Improvement in other functional outcomes such as socialization skills, self-esteem, and improved play themes were demonstrated in some, but not all, of the 4 studies that measured them. In general, studies of interventions were small and heterogeneous, may be subject to plateau effects, and reported short-term outcomes based on various instruments and measures. As a result, long-term outcomes are not known, interventions could not be compared directly, and generalizability is questionable. Use of risk factors to guide selective screening is not supported by studies. Several aspects of screening have been inadequately studied to determine optimal methods, including which instrument to use, the age at which to screen, and which interval is most useful. Trials of interventions demonstrate improvement in some outcome measures, but conclusions and generalizability are limited. Data are not available addressing other key issues including the effectiveness of screening in primary care settings, role of enhanced surveillance by primary care physicians before referral for diagnostic evaluation, non-speech and language and long-term benefits of interventions, and adverse effects of screening and interventions.

Screening for hepatitis C virus infection: a review of the evidence for the U.S. Preventive Services Task Force.

Hepatitis C virus (HCV) is the most common bloodborne pathogen in the United States and is an important cause of patient morbidity and mortality, but it is unclear whether screening to identify asymptomatic infected persons is appropriate. To synthesize the evidence on risks and benefits of screening for HCV infection. MEDLINE (through February 2003), Cochrane Clinical Trials Registry (2002, Issue 2), reference lists, and experts. Controlled studies of screening and antiviral therapy and observational studies on other interventions, risk factors, accuracy of antibody testing, work-up, harms of biopsy, and long-term outcomes. Using preset criteria, the authors assessed the quality of included studies and abstracted information about settings, patients, interventions, and outcomes. There are no published trials of screening for HCV infection. Approximately 2% of U.S. adults have HCV antibodies, with the majority having chronic infection. Risk factor assessment could identify adults at substantially higher risk. Antiviral treatment can result in a sustained virologic response rate of 54% to 56%, but no trials have been done specifically in asymptomatic patients likely to be identified by screening. Data are insufficient to determine whether treatment improves long-term outcomes. There are no data to estimate the benefit from counseling or immunizations. Although risks of biopsy and treatment appear minimal or self-limited, data on other adverse effects of screening, such as labeling or anxiety, are sparse. Antiviral treatment can successfully eradicate HCV, but data on long-term outcomes in populations likely to be identified by screening are lacking. Although the yield from targeted screening, particularly in intravenous drug users, would be substantially higher than in the general population, data are inadequate to accurately weigh the overall benefits and risks of screening in otherwise healthy asymptomatic adults.

EUSOMA review of mammography screening

In 1993 the European Society of Mastology concluded that regular mammography screening reduces the riskof dying from breast cancer. The evidence came from a meta-analysis of six randomised controlled trials that collectively showed a statistically significant 22% reduction in breast cancer mortality. The effect is clear in women aged ≥50 years but there is uncertainty in women aged <50 years. Screening programmes for women aged ≥50 years should be part of organised public health programmes. The adverse effects of screening were addressed and performance indicators of programmes were specified.

Clinical impact of introduction of mammography screening in a non-screening country with special reference to the Copenhagen service mammography screening programme.

As stated in the European guidelines for quality assurance in mammography screening, the objective of screening for breast cancer is to reduce morbidity and mortality from the disease without adversely affecting the health status of those who participate in screening (1). The effectiveness of a programme therefore relies on the quality, organisation, and population acceptability. When organising a screening programme, baseline epidemiological data is a prerequisite upon which the outcome measures of mammography screening must be compared, since a more favourable stage distribution in screen-detected cancers compared to clinically diagnosed cancers forms the basis of the mortality reduction (2). It has repeatedly been shown that tumour stage correlates with survival in breast cancer (3, 4). An early predictor of the effect of screening on breast cancer mortality is therefore an indubitable increase in early stage breast cancer incidence with the onset of screening, and a subsequent decrease in more advanced stage breast cancer incidence (5). The obtained change in stage distribution brought about by screening should also result in a higher degree of breast conserving therapy and a decrease in need of adjuvant treatment (6). Among the adverse effects of screening is the risk of a false positive mammography leading to a certain number of healthy women recalled for further assessment, and, further, the risk of overdiagnosis with mammographic detection of small, indolent malignancies, that might not have surfaced clinically in the absence of screening. In order to monitor the effects of a screening programme the European guidelines have set up performance indicators stating acceptable levels for the quality of the screening process, and early surrogate indicators by which the impact of a breast cancer screening programme can be assessed (1). These indicators are used as surrogate measures of the likelihood of achieving a subsequent mortality reduction (7). This review focuses on the clinical impact of introduction of mammography screening, exemplified by comparison of tumour stage and treatment of breast cancer detected by mammography screening with clinically detected breast cancers.

Cervical cancer screening. Human benefits and human costs in the evaluation of screening programmes

INTRODUCTION THE SCIENTIFIC evidence of the effectiveness of screening for cervical cancer in reducing the incidence and mortality is well established and acknowledged by the scientific community [ 1, 21. Screening programmes are applicable as public health policy [ 1, 21. However, although screening is widespread in European countries, the potential benefits of screening have not been achieved. This is partly because smears are not distributed in an optimal way, and partly because the standards of screening vary across countries. Homogenous standards are necessary in order to make comparable evaluations of the effectiveness and quality of different screening programmes. Quality assurance guidelines have to be adopted for increasing the potential benefits and, no less important, for reducing the potential adverse effects of cervical cancer screening. The scientific evidence concerning human benefits and human costs of cervical screening form the background for the evaluation of effectiveness and for the definition of quality assurance standards. From the ethical point of view, the duty of carefully evaluating the adverse effects of screening is strengthened by the fact that screening addresses healthy people.

PRINCIPLES OF CANCER SCREENING FOR CLINICIANS

This chapter has outlined some principles of tumor growth, test characteristics, and the evaluation of screening technologies. We have emphasized that test specificity is the critical parameter in the evaluation of technologies because it is the healthy people who will suffer the most from the adverse effects of screening. We have also emphasized that the efficacy of a test is best evaluated by examining mortality reductions in comparable populations. The purpose has been to assist clinicians with their interpretation of the literature. Busy clinicians may not always have the time or inclination to do this themselves. In those cases they need to examine how organizations who make recommendations are coming to their conclusions because it is physicians, not organizations that will do the screening. In particular, it is important to ask the following: (1) Were criteria followed to justify the recommendations being made? (2) If so, what were they, and can the organization demonstrate that they are being met? (3) What perspectives and biases do the organizations bring to the judgments they inevitably have to make? (4) Do you share those perspectives? and (5) When the recommendation is adopted, can you guarantee that it will "first do no harm."

How serious are the adverse effects of screening?

The adverse effects of screening are not commonly studied. False-positive tests lead to discomfort, costs, and risks from additional diagnostic and therapeutic procedures. False-negative tests lead to a sense of security and delays in seeking medical help when symptoms develop. Labeling an individual with a false-positive test, or with a true-positive test for which there is no evidence that intervention makes a difference, e.g., intervention on an 80-year-old asymptomatic woman with hypercholesterolemia, can have a markedly negative impact on the quality of life. Interpreting statistical abnormalities out of clinical context, e.g., lending importance to a multiphasic blood screen showing "high" alkaline phosphatase in a teenager, leads to unnecessary costs and anxiety. The cost of screening programs that may not have been shown to do more good than harm is already having an impact on the resources available to diagnose and treatment symptomatic persons. Premature implementation of unproved screening programs will continue to decrease physician and public confidence in prevention.

Basic Issues in Population Screening for Cancer&lt;xref ref-type="fn" rid="FN2"&gt;2&lt;/xref&gt;&lt;xref ref-type="fn" rid="FN3"&gt;3&lt;/xref&gt;

The value of population screening as an approach to cancer control is controversial because the objectives, benefits, costs, and potential adverse effects of screening programs are not widely agreed upon, nor are the many difficulties involved in evaluating a cancer screening program well recognized. A review of the issues pertinent to cancer screening and their interrelationships is presented. The characteristics of a particular cancer that should be considered before it becomes the target of a screening program are described; emphasis is placed on the prevalence of the detectable preclinical phase. The features of a good screening test are reviewed and the importance of specificity is indicated. Methods for evaluation of screening programs are considered, and the need for measurement of the effects of screening on the mortality rate is emphasized. The biases inherent in some commonly used evaluation procedures, especially lead time bias and length bias, are discussed. The possible adverse effects of cancer screening are pointed out, especially its capacity to increase morbidity. Several approaches to improving cancer screening programs are presented. Finally, the relevance of knowledge regarding the optimum interscreening interval to cancer control and to research issues is described.