Cancer Prevention in Primary Care: Screening for ovarian, prostatic, and testicular cancers

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Screening: general considerations Before a screening programme is introduced several criteria need to be satisfied and the benefits and disadvantages of screening need to be assessed, as discussed in the first article (28 May, p 1418) (boxes 1 and 2). Screening should not be contemplated unless it has been shown to be effective in reducing mortality and to be worth the costs to individual people (anxiety, inconvenience, undergong unnecessary medical procedures) and to the health service (allocation of scarce resources). Screening must also be sustainable in terms of recruitment, quality of the procedures undertaken, and follow up. Box 3 shows the factors influencing the effectiveness of a cancer screening programme, and table I shows the requirements for the performance of screening tests. In this and the next article, on colorectal cancer, I consider screening for cancers for which the criteria for screening have not yet been fulfilled and at least in some cases the potential benefit of screening might be outweighed by the risk of harm and the costs incurred. Box 1 - Criteria for screening* Is the condition an important health problem? Is there a recognisable early stage? Is treatment at an early stage more beneficial than at a later stage? Is there a suitable test? Is the test acceptable to the population? Are there adequate facilities for diagnosis and treatment? What are the costs and benefits? Which subgroups should be screened? How often should screening take place? Modified from wilson and Jungner1 Box 2 - Benefits and disadvantages of screening Benefits Improved prognosis for some cases detected by screening Less radical treatment for some early cases Reassurance for those with negative test results Disadvantages Longer morbidity in cases whose prognosis is unaltered Overtreatment of questionable abnormalities False reassurance for those with false negative results Anxiety and sometimes morbidity for those with false positive results Unnecessary medical intervention in those with false positive results Hazard of screening test Resource costs: diversion of scarce resources to screening programme Box 3 - Factors influencing the effectiveness of a cancer screening programme Participation of the target population Sensitivity of the screening test - that is, not too many false negative results Specificity of the screening test - that is, not too many false positive results Frequency of routine screening Adequacy of follow up of those with abnormal results Effectiveness of treatment of those with cancer View this table: In this window In a new window TABLE I Performance of screening tests Screeing for ovarian cancer Ovarian cancer: current facts Ovarian cancer is the fifth commonest cancer in women, with 5830 new cases occurring in the United Kingdom in 1988. Most (90%) cases occur in women over 45. The overall prognosis is poor. In 1992, 4360 women died of ovarian cancer in the United Kingdom. It accounts for nearly 6% of all deaths from cancer in women and is the cause of more deaths in women than for all other gynaecological malignancies combined. Because of the lack of early symptoms, 65-75% of cases present at an advanced stage of disease. The overall five year relative survival rate is 28%, but the five year survival rate for stages III and IV combined is only 10%. A five year survival rate greater than 90% may be achieved for the small minority of women with disease confined to the ovary at diagnosis. The quality of initial surgery is an important prognostic factor and, recently, significant differences in survival have been reported between teaching and non-teaching hospitals. Prospects for screening The correlation between five year survival rates and stage at diagnosis has long suggested that early detection may improve prognosis. No randomised controlled studies of screening for ovarian cancer have yet been conducted (although one has just begun), so there is as yet no evidence that early detection by screening reduces mortality from ovarian cancer. Box 4 shows some of the problems with screening for ovarian cancer. The underline the importance of conducting randomised trials of such screening. Box 4 - Problems is screening for ovarian cancer Lack of evidence that early detection reduces mortality Lack of understanding how ovarian cancer develops No single test has both high enough sensitivity and high enough specificity to screen for early ovarian cancer, but combining tests looks promising Lack of evidence of the balance of the benefit of screening to possible harm Lack of conclusive evidence of the acceptability of the current tests to the general population Inability at present to determine a high risk population suitable for screening Screening tests During the past 10 years large prospective studies have provided information about the use of the antigen marker serum CA 125, abdominal ultrasonography, transvaginal ultrasonography, and bimanual pelvic examinations in screening for ovarian cancer. These studies have been uncontrolled and based on relatively small self selected populations. Additional techniques, including other serum antigen markers, intraovarian colour Doppler flow mapping, and radioimmunoscintigraphy are being evaluated for their ability to distinguish between early malignant and benign masses. Requirements for screening test The overall incidence of ovarian cancer in the general female population is low. This places limitations on the performance of prospective screening tests (table I). In the United Kingdom, where the incidence for all ages is 1 in 5000, the use of a test with 100% sensitivity and 99% specificity for ovarian cancer in the general female population would result in one case of cancer being diagnosed for 5000 women screened; 50 women would have a false positive result. As the likely consequence of an abnormal result on screening is surgery, the positive predictive value of an abnormal test must be high for the screening procedure...