The interpretation of time trends

The requirements for valid comparison over time of cancer incidence and mortality are given in the opening paragraphs of this chapter. Among the more important of these is comparability between ICD revisions. Yet those entrusted with the decennial revisions of the International Statistical Classification of Diseases, Injuries and Causes of Death (ICD) have to try to reconcile several frequently contradictory demands. These include (a) meeting the needs of an ever widening number of users (hence, the change in title for the 10th revision to International Statistical Classification of Diseases and Related Health Problems); (b) incorporation of advances in the understanding of the biology of disease while avoiding ephemeral notions and classifications; and (c) the preservation of the continuity of time series. These desiderata have not always been met: some of the resulting problems have been discussed above. Despite the foregoing, the comparison of time trends in cancer incidence and mortality is a valid and useful exercise particularly when the investigator systematically considers the possible sources of bias and error. A low rate, if based on over a million person-years of observation, is, if underregistration can be ruled out, likely to reflect reality. Nevertheless, the smaller the number of cases and the greater the standard error of the rate, notably for the less frequent sites and the rarer histological types, the more attention needs to be paid to questions of possible artefact. Should the data for a given area or time period appear out of line with what might be expected, it may be worthwhile to check with the registry in question to see whether the trend could be explained on the basis of local circumstances, custom or practice. A formal review of the evidence for an apparent change over time, drawing on the experience of epidemiologists, pathologists and clinicians, as for example in non-Hodgkin's lymphoma, can be very useful (Levine and Hoover, 1992). Hitherto, much of the study of time trends of both incidence and mortality, notably those comparing international data, has been based on data published at the level of three digits in the ICD. Although such analyses will continue to be illuminating, future work is likely to give much greater emphasis to subsite and histological type, information that is difficult to publish routinely.(ABSTRACT TRUNCATED AT 400 WORDS)

Further follow up of mortality and incidence of cancer in men from the United Kingdom who participated in the United Kingdom's atmospheric nuclear weapon tests and experimental programmes

OBJECTIVES

To study the long term effects of participation in the United Kingdom's atmospheric nuclear weapon tests and experimental programmes and to test hypotheses generated by an earlier report, including the possibility that participation in tests caused small hazards of leukaemia and multiple myeloma.

DESIGN

Follow up study of mortality and cancer incidence.

SUBJECTS

21,358 servicemen and civilians from the United Kingdom who participated in the tests and a control group of 22,333 non-participants.

MAIN OUTCOME MEASURES

Numbers of deaths; standardised mortality ratios; relative risks of mortality from all causes and 27 types of cancer.

RESULTS

During seven further years of follow up the numbers of deaths observed in participants were fewer than expected from national rates for all causes, all neoplasms, leukaemia, and multiple myeloma (standardised mortality ratios 0.86, 0.85, 0.57, and 0.46); death rates were lower than in controls (relative risks 0.99, 0.96, 0.57, and 0.57; 90% confidence intervals all included 1.00). In the period more than 10 years after the initial participation in tests the relative risk of death in participants compared with controls was near unity for all causes (relative risk 0.99 (0.95 to 1.04) and all neoplasms (0.95 (0.87 to 1.04)); it was raised for bladder cancer (2.69 (1.42 to 5.20)) and reduced for cancers of the mouth, tongue, and pharynx (0.45 (0.22 to 0.93)) and for lung cancer (0.85 (0.73 to 0.99)). For leukaemia mortality was equal to that expected from national rates but greater than in controls for both the whole follow up period (1.75 (1.01 to 3.06)) and the period 2-25 years after the tests (3.38 (1.45 to 8.25)).

CONCLUSION

Participation in nuclear weapon tests had no detectable effect on expectation of life or on subsequent risk of developing cancer or other fatal diseases. The excess of leukaemia in participants compared with controls seems to be principally due to a chance deficit in the controls, but the possibility that participation in the tests may have caused a small risk of leukaemia in the early years afterwards cannot be ruled out.

Sir Austin Bradford Hill and the progress of medical science

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Health and the environment in the 1990s

Expectation of life at birth provides a simple measure of the state of health of a country. Differences in the expectation are examined in the United States over time and between males and females and Whites and non-Whites, and worldwide between market and nonmarket developed countries, and between developed and developing countries. The principal factors responsible for the trends and the current differences are changes in the social and physical environment, in personal behavior, and in medical care, and their relative importance is assessed. It is concluded that, at present, the principal environmental hazards worldwide are those associated with poverty of individuals within the market economies and of communities in the developing countries and that in the future, they will be the effects of overpopulation and the production of greenhouse gases.

Molecular diagnostics for myelin proteolipid protein gene mutations in Pelizaeus-Merzbacher disease

Pelizaeus-Merzbacher disease (PMD) is a clinically heterogeneous, slowly progressive leukodystrophy. The recent detection of mutations in the myelin proteolipid protein (PLP) gene in several PMD patients offers the opportunity both to design DNA-based tests that would be useful in diagnosing a proportion of PMD cases and, in particular, to evaluate the diagnostic utility of single-strand conformation polymorphism (SSCP) analysis for this disease. A combination of SSCP analysis and direct sequencing of PCR-amplified DNA was used to screen for PLP mutations in 24 patients affected with leukodystrophies of unknown etiology. Two heretofore undescribed mutations in the PLP gene were identified, Asp202His in exon 4 and Gly73Arg in exon 3. The ease and efficiency of SSCP analysis in detecting new mutations support the utilization of this technique in screening for PLP mutations in patients with unexplained leukodystrophies.

Trends in childhood leukaemia in the Nordic countries in relation to fallout from atmospheric nuclear weapons testing

OBJECTIVE

To obtain further information about the risks of childhood leukaemia after exposure to ionising radiation at low doses and low dose rates before or after birth or to the father's testes shortly before conception.

DESIGN

Observational study of trends in incidence of childhood leukaemia in relation to estimated radiation exposures due to fallout from atmospheric nuclear weapons testing during the 1950s and 1960s.

SETTING

Nordic countries.

SUBJECTS

Children aged under 15 years.

MAIN OUTCOME MEASURES

Incidence rates of leukaemia by age at diagnosis, sex, country, and calendar year of diagnosis or year of birth; exposure category; relation between leukaemia and exposure for children aged 0-14 and 0-4 separately.

RESULTS

During the high fallout period the average estimated dose equivalent to the fetal red bone marrow was around 140 mu Sv and the average annual testicular dose 140 mu Sv. There was little evidence of increased incidence of leukaemia among children born in these years. Doses to the red bone marrow of a child after birth were higher, and during the high exposure period children would have been subjected to an additional dose equivalent of around 1500 mu Sv, similar to doses received by children in several parts of central and eastern Europe owing to the Chernobyl accident and about 50% greater than the annual dose equivalent to the red bone marrow of a child from natural radiation. leukaemia incidence and red marrow dose was not related overall, but rates of leukaemia in the high exposure period were slightly higher than in the surrounding medium exposure period (relative risk for ages 0-14: 1.07, 95% confidence interval 1.00 to 1.14; for ages 0-4: 1.11, 1.00 to 1.24).

CONCLUSIONS

Current predicted risks of childhood leukaemia after exposure to radiation are not greatly underestimated for low dose rate exposures.

The lessons of life: keynote address to the nutrition and cancer conference

Some 15 years ago there began to emerge a consensus among epidemiologists that diet might be responsible for 30-60% of cancers in the developed world, in the sense that it should be possible to reduce age-specific incidence rates by this amount by practicable dietary change. Within about 6 years it was also broadly agreed that the principal changes required to bring about this effect were a reduction in the consumption of fat; an increase in the consumption of fruit, green and yellow vegetables, dietary fiber, and some micronutrients; and possibly an improvement in the methods of food preservation. Very small effects, if any, were attributed to food additives and to the pollution of food by trace pesticides, which the public, who accepted much of the consensus advice, have increasingly regarded as important causes of risk. These past conclusions are reviewed in the light of increased knowledge of the etiology of cancer and the trends in its incidence. Contrary to common belief, the trends are broadly encouraging.

Urban and rural factors in the aetiology of cancer

The incidence of cancer, or the mortality attributed to it, has been compared in urban and rural residents in 13 populations. In each case, the incidence (or mortality) has been higher in the urban areas in each sex, the ratios varying from a minimum of 1.03 to 1 in men in Japan to 1.63 to 1 in men in Denmark. Examination of 26 separate types of cancer showed that 23 tended to be more common in towns, 1 (myeloma) to be evenly distributed, and 2 (cancers of the lip and eye) to be more common in the countryside. The urban excess was greatest for cancers of the bladder, larynx, liver, lung, mouth and pharynx, and oesophagus, and least for leukaemia and non-Hodgkin's lymphoma. It is concluded that differences in personal behaviour (cigarette smoking, alcohol consumption, sexual promiscuity, exposure to ultraviolet light, type of diet, and family size) are the principal factors responsible for the urban excess. Other factors include general atmospheric pollution, occupational hazards, genetic differences in susceptibility, and artefacts of diagnosis and recording. The rural excess was marked for cancer of the lip in both sexes, but less marked and clearly evident only in men for cancer of the eye. Three-quarters of eye cancers are melanomas and the excess incidence in rural areas provides some weak support for the idea that exposure to sunlight contributes to the production of the disease.

Completeness of follow up in a cohort study of mortality using the United Kingdom National Health Service Central Registers and records held by the Department of Social Security

STUDY OBJECTIVE

The aim was to evaluate and improve the completeness of follow up in a cohort study of mortality carried out using the UK National Health Service (NHS) Central Registers.

SETTING

This was a follow up study of UK servicemen who served abroad in the 1950s and 1960s, including those who participated in the UK atmospheric nuclear weapon tests and experimental programmes.

DESIGN

Details of men for whom follow up achieved using the NHS Central Registers was unsatisfactory were submitted to the Department of Social Security (DSS) for tracing, as were details of men born before 1916 and reported by the NHS Central Registers as currently registered with a general practitioner, and a 1% sample of remaining men born in or after 1916.

MEASUREMENTS AND MAIN RESULTS

The additional follow up increased the number of deaths fully identified in the cohort by 6.5%. Mortality among those untraced on the NHS Central Registers was substantially greater than in the cohort as a whole (10.2% v 6.9%). Among those reported by the NHS Central Registers as not currently registered with a general practitioner, 2.7% were found to have died, as were 1.1% of men born before 1916 and currently reported to be registered with a general practitioner. As expected there was clear evidence that information about emigrations supplied by both the NHS Central Registers and DSS is far from complete.

CONCLUSION

Standardised mortality ratios based on follow up via the NHS Central Registers alone are likely to be somewhat low, and this should be borne in mind when interpreting the data.

Mortality among United Kingdom servicemen who served abroad in the 1950s and 1960s

The Registrar General's decennial supplements on occupational mortality provide only limited information on mortality in the armed forces in the United Kingdom. Mortality has therefore been studied among a group of 30,619 United Kingdom servicemen who served abroad in tropical or desert areas in the 1950s and 1960s, and who remained in the services for a total of at least five years. Mortality from all causes of death, all neoplasms, and all other known non-violent causes was lower than that expected from rates for all men in England and Wales, whereas mortality from accidents and violence was raised. These differences remained after adjustment for social class, affected both officers and other ranks, and had not disappeared even after the men had been followed up for at least 20 years. When mortality from 20 specific cancers and 10 other disease groups was examined there were significant excesses for cancers of the oesophagus (standardised mortality ratio (SMR) = 146; p = 0.03) and prostate (SMR = 156; p = 0.03), and significant deficits for cancers of the lung (SMR = 73; p less than 0.001), stomach (SMR = 66; p = 0.002), bladder (SMR = 53; p = 0.02), other specified neoplasms (SMR = 48; p = 0.001), coronary heart disease (SMR = 76; p less than 0.001), bronchitis, emphysema, and chronic obstructive lung disease (SMR = 42; p less than 0.001), and for five further groups of diseases unrelated to smoking or alcohol. Examination of mortality in each of the three services separately identified two specific hazards in the Royal Navy; seven deaths from mesothelioma occurred compared with less than 2.06 expected (p less than 0.005), and there was also an excess of neoplasms and of other diseases associated with alcohol (SMRs of 181 and 229; p = 0.002 and less than 0.001). Mortality from smoking related diseases other than those associated with alcohol was low in all three services, particularly among officers.

Experiences of a battalion medical officer in the retreat to Dunkirk: V

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Time from infection with HIV to onset of AIDS in patients with haemophilia in the UK

The two-stage parametric regression model of Brookmeyer and Goedert has been adapted and fitted to data on the development of AIDS in haemophiliacs in the UK who are seropositive for HIV. The risk of developing AIDS by a given time following seroconversion increases with increasing age at seroconversion. It is likely that the risk increases smoothly with age, although the data have been analysed in three age categories, and it is estimated that by seven years after seroconversion 6 per cent of patients aged under 25 at seroconversion, 20 per cent of those aged 25-44 and 34 per cent of those aged 45 or more have developed AIDS. For a given age at seroconversion the annual risk of developing AIDS increases with increasing time after seroconversion, and at seven years the annual risks of developing AIDS during the next year in the three age groups are estimated to be 2 per cent for those aged less than 25 at seroconversion, and 10 and 11 per cent respectively for those aged 25-44 and 45 or more.

Experiences of a battalion medical officer in the retreat to Dunkirk: IV

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