N. E. Day

TRENDS IN MORTALITY FROM CERVICAL CANCER IN THE NORDIC COUNTRIES: ASSOCIATION WITH ORGANISED SCREENING PROGRAMMES

Time trends in mortality from cervical cancer in Denmark, Finland, Iceland, Norway, and Sweden since the early 1950s were investigated in relation to the extent and intensity of organised screening programmes in these countries. In all five countries the cumulative mortality rates (0-74 years) fell between 1965 and 1982. In Iceland, where the nationwide programme has the widest target age range, the fall in mortality was greatest (80%). Finland and Sweden have nationwide programmes also; the mortality fell by 50% and 34%, respectively. In Denmark, where about 40% of the population are covered by organised programmes, the overall mortality fell by 25%, but in Norway, with only 5% of the population covered by organised screening, the mortality fell by only 10%. The results support the conclusion that organised screening programmes have had a major impact on the reduction in mortality from cervical cancer in the Nordic countries.

REDUCTION OF BREAST CANCER MORTALITY THROUGH MASS SCREENING WITH MODERN MAMMOGRAPHY: First Results of the Nijmegen Project, 1975 - 1981

Since 1975 four rounds of screening with modern mammography for breast cancer have been carried out among 30 000 Nijmegen women born before 1940. The results up to the end of 1981 shows that the odds ratio of screened vs unscreened subjects among women who died from breast cancer compared with women who did not, was 0.48 (95% confidence interval 0.23-1.00) in all age groups.

EVALUATION OF SCREENING FOR BREAST CANCER IN A NON-RANDOMISED STUDY (THE DOM PROJECT) BY MEANS OF A CASE-CONTROL STUDY

In 1974 a non-randomised study of the effect of mass screening by physical examination and xeromammography on mortality from breast cancer was started. Of the 20 555 eligible women in the city of Utrecht born between 1911 and 1925 (aged 50-64 at the start of the study), 14 796 attended for screening. Four rounds of screening were carried out. The relative risk of dying from breast cancer among women ever screened compared with women never screened was 0.30 (95% confidence interval 0.13-0.70).

Breast cancer screening programmes: the development of a monitoring and evaluation system.

It is important that the introduction of breast screening is closely monitored. The anticipated effect on breast cancer mortality will take 10 years or more fully to emerge, and will only occur if a succession of more short-term end points are met. Data from the Swedish two-county randomised trial provide targets that should be achieved, following a logical progression of compliance with the initial invitation, prevalence and stage distribution at the prevalence screen, the rate of interval cancers after the initial screen, the pick-up rate and stage distribution at later screening tests, the rate of interval cancers after later tests, the absolute rate of advanced cancer and finally the breast cancer mortality rate. For evaluation purposes, historical data on stage at diagnosis is desirable; it is suggested that tumour size is probably the most relevant variable available in most cases.

Diet and cancer of the stomach: a case-control study in Greece.

A case‐control study focusing on the role of diet in the etiology of gastric cancer was undertaken in Piraeus, the sister city of Athens, in a population characterized by ethnic homogeneity but substantial heterogeneity with respect to dietary habits. The case series consisted of 110 consecutive patients with histologically confirmed adenocarcinoma of the stomach, admitted to two teaching hospitals during a 3‐year period; the control series consisted of orthopedic patients admitted to a nearby hospital for accidents, fractures and other orthopedic disorders, during the same time period. Dietary histories concerning the frequency of consumption (per month or per week) of about 80 food items were obtained by the same interviewer. Cases reported significantly less frequent consumption of lemons, oranges, brown bread, and raw, salad‐type vegetables (particularly lettuce, onions and cucumbers) and, independently, significantly more frequent consumption of pasta, beans and nuts. A relative risk of about 40 was found between extreme quintiles when the above 9 food Items were combined in a linear risk score. Use of an index constructed from the study material will clearly overestimate the level of risk between the extreme quintiles, but nevertheless the risk differences appear noteworthy, and consistent with the international variation in the incidence of gastric cancer. No significant associations were found with alcoholic beverages, coffee or tea.

Indirect standardization and multiplicative models for rates, with reference to the age adjustment of cancer incidence and relative frequency data.

Abstract By assuming that a simple multiplicative relationship exists between the age-specific mortality or morbidity rates for several populations, one is led to comparison of these populations using indirectly standardized mortality or morbidity ratios (SMR) where the age-specific rates for all populations combined are used as standards. Adjustments to these ratios are needed in case of large differences among the populations in both age-specific rates and age structures. This method is appropriate when insufficient data are available for direct standardization or when numbers of cases in individual age groups are so small as to make directly standardized rates unstable. It is oriented towards the internal comparison of specific sets of populations rather than production of synoptic figures for official publication. Extensions of the multiplicative hypothesis to the simultaneous analysis of multiple causes of mortality or morbidity suggest the use of a standardized relative mortality ratio (SRMR) for making comparisons when age-specific population denominators are not available. These methods are used to study several sets of cancer incidence and relative frequency data.

Statistical Methods in Cancer Research, Vol. 2, The Design and Analysis of Cohort Studies.

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Case-control studies for the evaluation of screening

The case-control approach has been proposed for the evaluation of the efficacy of screening for cancer. It provides information at the level of the individual subject and allows direct estimation of the relative risk of not being screened. The criteria for the choice of the case and control series are examined, with reference to the type of cancer considered and the precise goal assigned to the screening programme. The definition of the exposure is discussed, as well as criteria for the avoidance of commonly occurring biases. Typical situations where case-control studies of screening efficacy appear to be the method of choice are presented.

Estimating the sensitivity of a screening test.

A commonly used estimate of a screening tests sensitivity, based on the prevalence at screening and the incidence of interval cancers, is shown to be logically unsound and quantitatively poor. An alternative simple estimate is proposed, based only on incidence rates.

NO EFFECT OF RIBOFLAVINE, RETINOL, AND ZINC ON PREVALENCE OF PRECANCEROUS LESIONS OF OESOPHAGUS: Randomised Double-blind Intervention Study in High-risk Population of China

A randomised double-blind intervention trial was carried out in Huixian, Henan Province, Peoples Republic of China, to determine whether combined treatment with retinol, riboflavine, and zinc could lower the prevalence of precancerous lesions of the oesophagus. 610 subjects in the age group 35-64 were randomised to receive once a week the active treatment (15 mg [50 000 IU] retinol, 200 mg riboflavine, and 50 mg zinc) or placebo. Both at entry to the study and at the end of the treatment, 13.5 months later, the subjects were examined, with an emphasis on signs of vitamin A and riboflavine deficiences, and riboflavine, retinol, beta-carotene, and zinc levels were measured. Compliance was excellent. The final examination, on 567 (93%) subjects, included oesophagoscopy and at least two biopsies. The intervention did not affect the prevalence of oesophageal lesions: after one year, the prevalence of oesophagitis with or without atrophy or dysplasia was 45.3% in the placebo group and 48.9% in the vitamin/zinc treated group.