Epidemiology of cancer in ethnic groups.

Substantial differences in the level and patterns of cancer have long been known to exist. Thus, breast cancer mortality in England & Wales in 1908-1912 was ten times higher than in Japan. Today the risk differential is six-fold. The major geographical differences in cancer risk throughout the world are mentioned and the significance of study of changes in cancer risk in migrant populations is emphasised. Thus, while cancer of the large bowel is still relatively uncommon in Japan, the incidence in US Japanese is currently higher than in both US Whites and Blacks. As the Japanese have not changed their genes, it is likely that the higher levels of risk in the US are due to the environment. Within Singapore there are substantial differences in the risk of cancers of the nasopharynx and oesophagus between the various Chinese dialect groups. The information available on ethnic differences in cancer risk in the UK are reviewed. Current analyses are flawed by failure to distinguish between ethnic groups coming from the same continent. The collection of data on ethnic group at the 1991 census and the recently introduced requirement that this also be collected in hospital records will permit direct calculation of incidence and replace anecdote by fact.

Will the Scottish Cancer Target for the year 2000 be met? The use of cancer registration and death records to predict future cancer incidence and mortality in Scotland.

Cancer mortality data reflect disease incidence and the effectiveness of treatment. Incidence data, however, reflect the burden of disease in the population and indicate the need for prevention measures, diagnostic services and cancer treatment facilities. Monitoring of targets mandates that both be considered. The Scottish Cancer Target, established in 1991, proposed that a reduction of 15% in mortality from cancer in the under-65s should be achieved between 1986 and 2000. Each year in Scotland approximately 8300 persons under 65 are diagnosed with cancer and 4500 die from the disease. The most common malignancies, in terms of both incident cases and deaths, in the under-65s, are lung and large bowel cancer in males, and breast, large bowel and lung cancer in females. A decrease of 6% in the number of cancer cases diagnosed in males under 65 is predicted between 1986 and 2000, whereas the number of cases in females in the year 2000 is expected to remain at the 1986 level. In contrast, substantial reductions in mortality are expected for both sexes: 17% and 25% in males and females respectively. Demographic changes will influence the numbers of cancer cases and deaths in the Scottish population in the year 2000. However, long-term trends in the major risk factors, such as smoking, are likely to be the most important determinants of the future cancer burden.

Oesophageal and gastric cancer in Scotland 1960-90.

In Scotland over the last 31 years the incidence of gastric cancer has significantly declined by 0.6% per annum in males and 1.1% in females. In contrast, for oesophageal cancer, incidence rates have risen significantly by 3.0% and 2.0% per annum in males and females respectively. Increasing incidence of both adenocarcinomas and squamous carcinomas of the oesophagus in men and squamous and recently adenocarcinomas in women has been observed. This cannot be entirely accounted for by a growth in the proportion of histologically verified (HV) tumours over time. The incidence of adenocarcinoma of the stomach increased over the study period, most likely because of increasing proportions of HV tumours and improved diagnostic precision. Areas with high levels of deprivation in Scotland are strongly associated with high rates of oesophageal cancer in men, and of gastric cancer in both men and women. All these observations are discussed in the context of current knowledge of risk factors for these diseases.

Brain and other nervous system tumours.

Interpretation of time trends in incidence rates for cancers of brain and other and unspecified parts of nervous system is complicated by variation in registration efficiency over time and place, statistical instability of rates, changes in the ICD classification of the tumours, variation in registration practice for the benign and unspecified tumours over time and changes in methods of diagnosis. The reader will undoubtedly have the impression that in this chapter there are too many differences in the content of the data over time and place to have confidence in any of the conclusions drawn. To derive a well documented and sustainable assessment on secular trends will require an international collaborative study collecting incidence data for the malignant, benign, uncertain and unspecified tumours of the brain and other parts of the nervous system by histology and by method of diagnosis. By providing a separate rubric for the meninges, the 10th Revision of the ICD (WHO, 1993) should--combined with the morphology rubrics of the second edition of the International Classification of Diseases-Oncology (Percy et al 1990)--make such an endeavour somewhat easier. The data presented above nevertheless suggest that, as for several other cancer sites, on the whole there has been a slow overall increase in the incidence of brain and other and unspecified nervous system neoplasms on the order of 1-2% per year over the past 30 years. Increases appear to have been greater in older people. The extent to which these increases are due to the unquestioned improvements in methods and precision of diagnosis is not clear. Birth cohort data suggest that in recent years, this influence may have been greatest for those birth cohorts born prior to 1900, and this effect is unlikely to disappear until cohorts born about 1910-1920 have passed on. There is currently little evidence to support the contention that the recent increase in older people cannot be largely explained by improvements in diagnostic methods, wider access to medical care and more intensive investigation. Further work is needed.

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)

Cancer of the oesophagus: a global overview.

The geographical distribution of cancer of the oesophagus shows wide inter- and intra-national variation both in mortality and sex ratio. Numerous analytical studies have demonstrated alcohol and tobacco as important risk factors. Poor diet, particularly those lacking fresh fruit and vegetables, appears to be an equally important determinant in certain areas. In addition to alcohol and tobacco, Maté drinking in Southern South America independently increases risk. The possible role of thermal injury when Maté is drunk hot is still being investigated. Analysis of incidence data by histological subtype and site of disease has revealed rising rates for adenocarcinomas, generally of the lower third of the oesophagus, and predominantly in males. These data are paralleled by increasing rates of adenocarcinoma of the cardia of the stomach. The aetiology of these tumours in adjacent sites remains to be fully investigated but one known predisposing factor is the presence of Barrett's oesophagus. This poor prognosis disease does not appear amenable to widespread screening. Preventative measures would necessarily incorporate plans to reduce alcohol and tobacco use while improving the marginal diets of many populations.

Temporal change in diagnostic criteria as a cause of the increase of malignant melanoma over time is unlikely.

To assess whether the increase in malignant melanoma incidence could be due, at least in part, to changes in histological criteria of malignancy, pathologists in Australia, France, Italy, New Zealand, Norway, Sweden, the United Kingdom, the United States and the USSR reviewed diagnoses of 50 consecutive pigmented naevi (40 junctional and compound; 10 intradermal) and 20 consecutive malignant melanomas made in each participating centre around 1930, around 1955 and around 1980. Collaborating pathologists re-read the material, 2,665 cases in all, either from the original slide (82%) or from a recut block (17%), gave their diagnosis and indicated whether the lesion was benign (B), dubious benign (DB), dubious malignant (DM) or malignant (M). As the distribution of review diagnoses was much the same whether the original slide or one made from a recut block was read, the material was pooled. Overall, 2.8% of cases originally reported as B/DB were reviewed as DM/M, while 4.4% of the DM/M diagnoses were held to be B/DB. The shifts between categories were greatest around 1955 and least around 1980, suggesting increasing uniformity of interpretation. All available blocks were recut and sections sent to IARC for review: 1.7% (22) of 1293 B/DB diagnoses were considered to be DM/M and 3.3% (18) of 551 DM/M diagnoses were considered to have been B/DB. The consistently low frequency of shift in diagnostic category, whether the material was reviewed in the collaborating laboratories or by one pathologist at IARC, in a study designed to give maximum attention to those lesions--the junctional and compound naevi--in which a change in opinion as to malignancy would be most likely to arise, suggests that pathologists, irrespective of geographical location, are using common criteria. These findings argue against changes in histological interpretation as being responsible for more than a small portion of the continuous increase of some 3% to 8% per annum observed in malignant melanoma incidence. Other explanations, such as an increase in the frequency or potential for malignant transformation of precursor lesions, must be sought. The anatomical distribution of the malignant melanomas examined followed the usual site pattern by sex, and their thickness was observed to decrease over the period of the study in most centres.

The epidemiology of prostatic cancer. Geographical distribution and time-trends.

Prostate cancer is one of the most frequent tumours in males. Globally about 235,000 new cases were estimated to occur in 1980. The cancer is particularly frequent in North America, where rates in blacks are often double those in whites, and in several European countries, being rare in much of Asia. After migration to the US, Chinese and Japanese show substantial increases. Incidence may be distorted by inclusion of varying numbers of so-called 'latent' cancers; for some comparisons mortality data are preferable. 'Small' latent cancers seem to be uniformly distributed irrespective of the incidence of the clinically manifest form. The incidence of prostate cancer seems to be increasing in most populations, particularly in Asia and Eastern Europe. In general, mortality follows suit. Birth cohort analysis shows that for US non-whites, cohorts born before 1896-1900 showed an increase in mortality for all age groups, but the death rates fell for cohorts born subsequently, a phenomenon also observed in Australia and England and Wales.