Changes in the geographical and temporal patterns of cancer incidence among black gold miners working in South Africa, 1964-1996.

We describe here the results of the final 8 years of geographical and temporal data of a 33-year study of the cancer experience of 12.8 million man-years of black miners working on the gold fields of South Africa over the period 1964-96. These workers were recruited from 15 territories, the major areas during the most recent period being Lesotho (26.8%), Transkei (21.5%) and Mozambique (15%). The earliest analyses, 1964-71 and 1972-79, showed hepatocellular and oesophageal cancers to be the most frequent cancers. The final analysis, for 1989-96, however, shows marked temporal changes in the relative position of four cancers or grouped malignancies: respiratory cancer up by 236%, hepatocellular carcinoma down to 32%, oesophageal holding steady, and lymphatic system cancers up by 420%, almost certainly because of association with HIV/AIDS infection. Significant geographical variations occurring between the home areas of the miners are important, as mining operations have little to do with the cancers that develop. The causes are essentially socio-environmental rather than occupational, and this means that the rates of the major cancers in the miners are surrogate measures of the same cancers in the home areas.

South African asbestos: production, exports, and destinations, 1959-1993.

Production and export figures of South African asbestos were analyzed over 1959-1993. They show stable sales of chrysotile. Those of crocidolite and amosite reached their peaks in the mid-1970s, after which trade fell drastically, crocidolite to 5% of its earlier peak and amosite to nil. Factors responsible for these virtual collapses were health issues, stricter legislation in First World countries, and litigation. In 1992, 21 countries continued to import crocidolite, although in reduced quantities. In the early 1960s, Europe and North America were the major recipients of South African asbestos. By 1989-91, these regions were surpassed by the Far East, which took over 90% of chrysotile and 70% of amosite. For crocidolite at that time, the Middle East took nearly 40%, Europe 28%, and Africa 21%. This implies that the newly importing countries can confidently expect an increase in asbestos-related disease and death well into the twenty-first century, even if the trade ceased now.

The carcinogenicity of chrysotile asbestos.

In in vitro test systems, chrysotile is markedly toxic, causes chromosomal aberrations, and is capable of inducing morphological and preneoplastic transformation. In carefully designed animal experiments, chrysotile produces lung cancer and mesothelioma as effectively as do the amphiboles tested. Human population studies do not refute these experimental results. Chrysotile asbestos is carcinogenic to humans, especially for the induction of lung cancer and mesothelioma in exposed populations. For cancers of other sites, with the exception of laryngeal and possibly gastrointestinal cancer, the evidence for association with exposure to all forms of asbestos, including chrysotile, is not yet adequate for evaluation.

The changing pattern of cancer mortality in South Africa, 1949-1979.

The first paper in this series was published in 1975 and covered the period 1949 - 1969 for whites, coloureds and Asians in South Africa. This period is now extended to 30 years, from 1949 to 1979 inclusive, and includes data for urban blacks from 33 selected urban areas for the period 1968 - 1977. This information was superseded by data for all blacks, both rural and urban, in 1978. As this is available only for 2 years, the data are not included in this series, and all mention of blacks indicates information on urban blacks only. It is reassuring to know that mortality and geographical data for urban and rural blacks can now be separated from each other for comparative purposes, and that, in the future, transitional trends due to such striking phenomena as migratory labour and emigration to industrial areas can now be determined by the year. Finally, instead of expressing mortality rates per 100 000 of the population, a new method called the "cumulative rate or risk' is used, which is carefully defined. Changes in cancer patterns in all four major population groups are reflected graphically over the period 1949 - 1979 (blacks since 1968) by this method, and trends over this long period are discussed in terms of the frequency of cancers within each group, prognosis, aetiological factors and other related aspects.

Lung cancer 1978-1981 in the black peoples of South Africa.

Mortality data on lung cancer among the black populations of South Africa, newly available from the first ever nation-wide enumerations, are analysed for age-specific rates and significant geographical and intertribal variations. This study finds a higher incidence at younger ages than among whites, an urban excess similar to other population groups in South Africa and a higher incidence among the Xhosa than Zulu. It is suggested that an anti-smoking campaign is urgently required among blacks in South Africa.

Geographical distribution of certain cancers in South Africa, 1968-1972.

The geographical distributions of six major causes of cancer mortality in South Africa have been analysed for three population groups: White, Coloured and Asian. Because of the lack of comparable data, the majority Black population is not included. Geographical patterns are compared and discussed in the light of findings from other countries. In several cases the potential for aetiological follow-up is demonstrated.

Geographical distribution of lung and stomach cancers in South Africa, 1968-1972.

The geographical distribution of lung and stomach cancer among three races in South Africa (Whites, Coloureds and Asians) has been investigated for the years 1968-1972, and the patterns of the occurrence of cases of cancer have been tested stochastically and mapped both separately and together. Information was not available for the Black population. Distinct differences in the distribution of lung and stomach cancer were found. Possible explanations for these differences are discussed.

Eleven sites of cancer in black gold miners from Southern Africa: a geographic enquiry.

The 5-year study of cancer in black gold miners, 1964-68, previously reported (Robertson et al., 1971) has now been extended for a separate 8-year period, 1972-79. This allows analyses of all cancers together and of 6 less common sites of cancer severally: lymphosarcomas, colon and rectum, leukaemia, stomach, pancreas and buccal cavity and also of those too rare to classify. The malignancies are considered by territory of origin of the gold miners. Lesotho miners have significantly fewer (P less than 0.05) tumours of the lymphatic and haemopoietic tissues and Natal miners have the highest incidence rates for 5 of the 6 sites (excluding leukaemia). A simple grouping method is applied to determine which of the 11 sites of cancer in the miners have similar distributions in their 10 territories of origin. The aetiological implications of clusters over space of certain sites of cancer are discussed. Finally, temporal change over the years 1964-79 shows a significant decrease overall (P less than 0.01) in cases of lymphosarcomas and colo-rectal cancers and an increase (P less than 0.05) in stomach cancer. The rare tumour, Kaposi's sarcoma, has also decreased significantly between the 2 periods studied.

Analyses of cancer incidence in black gold miners from Southern Africa (1964-79).

As an extension of an earlier study covering the 8-year period 1965-71 (t1), the incidence of cancer in black gold miners over a second 8-year period, 1972-79 (t2) has been investigated. The population again totalled 2.9 million man-years of employment, an average of 363,800 men per year. Of the 903 cancers found in t2, primary liver cancer accounted for 45.4%, oesophageal cancer 19.8%, cancer of the respiratory system 11.2% and bladder cancer 2.7%. Analysis of these 4 common cancers by country or region of origin of the miners confirms for the most part the patterns of incidence found in the earlier survey and consolidated rates are therefore presented for the full 16-year period, 1964-79 (t3). The spatial distribution of primary liver cancer within Mozambique and oesphageal cancer within Transkei have been investigated for the periods t1, t2 and t3 and temporal changes of rate have been examined by individual years from 1964 to 1979. The geographical gradient of incidence for cancer of the oesophagus in Transkei has become less marked during the second period of the survey and the crude incidence rate for primary liver cancer in gold miners from Mozambique has continued to drop throughout the period of the survey.

A comparison of cancer mortality rates in South Africa with those in other countries.

Standardized mortality rates for eight major types of cancer (as well as for all types of cancer considered together) in four South African population groups are compared with each other and with rates in selected countries. Wide differences among the races in South Africa are displayed, and several rates are shown to parallel those in other population groups abroad. This lends support to the belief that socio-economic factors (rather than solely genetic factors) play the major role in cancer causation.

Cancer of the oesophagus and the use of tobacco and alcoholic beverages in Transkei, 1975-6.

A large questionnaire-based sample survey over a period of 2 years has collected information on tobacco and alcohol use among young and old, male and female respondents in three regions of Transkei selected on the basis of having proved contrasts of incidence experience from oesophageal cancer. Results show significant gradients of social fabric and of customary usage of tobacco and alcohol across the three incidence regions. In particular the concept is supported of a synergistic relationship between tobacco and alcohol when both are used by one individual, with the major role being played by tobacco, especially when smoked in pipes. Stress is also laid on contrasts between old and young on the assumption that dynamic shifts of mortality may be expected to follow as the young of today alter the patterns of intake established by their elders.