Burkitt's tumour in the West Nile District Uganda, 1961-5

Space-time clustering of childhood cancers: a systematic review and pooled analysis

The aetiology of childhood cancers remains largely unknown. Space–time clustering of cases might imply an aetiological role of infections. We aimed to review the evidence of space–time clustering of specific childhood cancers. We searched Medline and Embase for population-based studies that covered a pre-defined study area, included cases under 20 years of age and were published before July 2016. We extracted all space–time clustering tests and calculated the proportion of positive tests per diagnostic group. In a pooled analysis, we performed a Knox test of the number of pairs of cases close to each other in time and space pooled across studies. 70 studies met our eligibility criteria, 32 of which reported Knox tests. For leukaemia, the proportion of positive tests was higher than expected by chance at both time of diagnosis (26%) and birth (11%). The pooled analysis showed strong evidence of clustering at diagnosis for children aged 0–5 years for a spatial and temporal lag of 5 km and 6 months, respectively (p < 0.001). The evidence was mixed for lymphoma and tumours of the central nervous system. The current study suggests that leukaemia cases cluster in space–time due to an aetiological factor affecting children under 5 years of age. The observed pattern of clustering of young children close to time of diagnosis is compatible with Greaves’ delayed-infections-hypothesis.

A Role for RNA Viruses in the Pathogenesis of Burkitt's Lymphoma: The Need for Reappraisal

Certain infectious agents are associated with lymphomas, but the strength of the association varies geographically, suggesting that local environmental factors make important contributions to lymphomagenesis. Endemic Burkitt's Lymphoma has well-defined environmental requirements making it particularly suitable for research into local environmental factors. The Epstein-Barr virus and holoendemic Malaria are recognized as important cofactors in endemic Burkitt's Lymphoma and their contributions are discussed. Additionally, infection with Chikungunya Fever, a potentially oncogenic arbovirus, was associated with the onset of endemic Burkitt's Lymphoma in one study and also with space-time case clusters of the lymphoma. Chikungunya Virus has several characteristics typical of oncogenic viruses. The Flavivirus, Hepatitis C, a Class 1 Human Carcinogen, closely related to the arboviruses, Yellow Fever, and Dengue, is also more distantly related to Chikungunya Virus. The mechanisms of oncogenesis believed to operate in Hepatitis C lymphomagenesis are discussed, as is their potential applicability to Chikungunya Virus.

Spatial clustering of endemic Burkitt's lymphoma in high-risk regions of Kenya

Endemic Burkitt's lymphoma (eBL), the most common childhood cancer in sub-Saharan Africa, occurs at a high incidence in western Kenya, a region that also experiences holoendemic malaria. Holoendemic malaria has been identified as a co-factor in the etiology of this cancer. We hypothesized that eBL may cluster spatially within this region. Medical records for all eBL cases diagnosed from 1999 through 2004 at Nyanza Provincial General Hospital were reviewed for case residential information to examine this hypothesis. Two cluster detection methods, Anselin's Local Moran test for spatial autocorrelation and a spatial scan test statistic, were applied to this residential data to determine whether statistically significant high- and low-risk areas were present in the Province. During the 6-year study period, 272 children were diagnosed with eBL, with an average annual incidence of 2.15 cases per 100,000 children. Using Empirical Bayes smoothed rates, the Local Moran test identified 1 large multi-centered area of low eBL risk (p-values < 0.01) and 2 significant multi-centered clusters of high eBL risk (p-values < 0.001). The spatial scan detected 3 small independent low-risk areas (p-values < 0.02) and 2 high-risk clusters (p-values = 0.001), both similar in location to those identified from the Local Moran analysis. Significant spatial clustering of elevated eBL risk in high-malaria transmission regions and of reduced incidence where malaria is infrequent suggests that malaria plays a role in the complex eBL etiology, but that additional factors are also likely involved.

Is endemic Burkitt's lymphoma an alliance between three infections and a tumour promoter?

Malaria and Epstein-Barr virus (EBV), recognised cofactors for endemic Burkitt's lymphoma, are ubiquitous within the lymphoma belt of Africa, and, unless other cofactors are involved, the tumour should be much more common than it is. Malaria and EBV alone cannot account for the occasional shifting foci and space-time case clusters of endemic Burkitt's lymphoma. Arboviruses and plant tumour promoters are other possible local cofactors that could explain such characteristics. The geographical and age distributions of endemic Burkitt's lymphoma parallel those of potentially oncogenic, mosquito-borne arboviruses. Arboviruses seem to be associated with case clusters of endemic Burkitt's lymphoma, and symptoms compatible with arbovirus infection have been seen immediately before the onset of the tumour. RNA and DNA viruses, including EBV, are promoted by extracts of a commonly used plant, Euphorbia tirucalli, the distribution of which coincides with the boundaries of the lymphoma belt. Extracts of E tirucalli are tumour promoters and can induce the characteristic 8;14 translocation of endemic Burkitt's lymphoma in EBV-infected cell-lines. They also activate latent EBV in infected cells, enhance EBV-mediated cell transformation, and modulate EBV-specific immunity.

Parental occupation and intracranial neoplasms of childhood: anecdotal evidence from a unique occupational cancer cluster

Near the end of the data-collection phase of a case-control interview study of environmental factors and childhood brain tumors, an unusual space-time cluster was revealed. Not only had six genetically unrelated children been diagnosed with a primary intracranial tumor in a recent 2.4 year period in a rural county in Ohio, but each child had one parent employed by the same company (two mothers, four fathers). This represents an observed/expected ratio greater than 70 (p much less than 0.001). All tumors were microscopically confirmed, and all case parents worked at the facility in question for at least 1 year prior to conception, during the index pregnancy, and for at least 6 months after birth. The place of parental employment was an electronics firm (Standard Industrial Classification [SIC] group number 367, electronic components and accessories), where more than 100 chemical compounds are used by the company in a manufacturing process. Results of the cluster investigation are described, including a description of the case series. This cancer cluster is unique in that the index case series is composed of the offspring of workers, not the workers themselves.

Epstein-Barr virus: the hematologic and oncologic consequences of virus-host interaction

Varicella-zoster virus (VZV) and Epstein-Barr virus (EBV) are two of the human herpesviruses. The others include herpes simplex virus (HSV) type 1, HSV type 2, and cytomegalovirus (CMV). In a series of two articles, we review the clinical diseases caused by VZV and EBV infections; we pay particular attention to the manifestations of these two viral infections in immunosuppressed and immunocompromised patients. In addition to the clinical reviews, each of the two articles begins with a brief discussion of the molecular aspects of VZV and EBV, respectively; this introduction describes features of the genome and immunogenic viral proteins which have clinical relevance. A model for pathogenesis is included. The first review concerns VZV infections. Recent data about the DNA sequence of the entire VZV genome are included, as well as a review of the VZV glycoproteins. Primary VZV infection (chickenpox) and VZV reactivation (zoster) are described in detail in both healthy individuals and people with cancer. The decade-long VZV vaccine trials in children with leukemia receive special emphasis because they have engendered considerable interest and debate. The second review (published here) covers EBV infections. This virus has been implicated in the causation of a wide variety of human hematological and oncological disorders, besides classical infectious mononucleosis. In particular, Burkitt's lymphoma, nasopharyngeal carcinoma, and lymphoproliferative disorders are strongly associated with EBV infection of the transformed cells. In addition, immunologically mediated cytopenias occasionally follow EBV infection. Finally, treatment regimens with antiviral chemotherapy and other agents are discussed for both VZV and EBV infections.

Clustering of non-Hodgkin's lymphomas. A case study

Lymphomas developed in three genetically unrelated family members living in the same household over a period of one year. Two of the patients had diffuse histiocytic lymphoma, and one had nodular lymphocytic lymphoma. All three showed response to treatment initially, but two have had relapses and died. The "clustering" of lymphomas in this family suggests an environmental cause.

Cancer clusters: a myth or a method

Historically, cluster reports have been considered to be only marginally productive and generally discouraged as statistical artifacts. This report presents the results of a three year study involving in excess of 100 cancer cluster reports. The majority of these investigations represented statistical events; there were, however, some exceptions. Several of these reports were the basis for larger and more productive studies. A survey of the types of reports received, their sources and outcomes is presented. Examples of productive and nonproductive studies are highlighted to indicate decision points for selecting the most promising reports. Investigators are encouraged to consider cancer cluster reports from lay individuals as well as from more authoritative sources (i.e., tumor registries, physicians, medical-social workers). Investigators are also urged to perform actual field investigations of those reports choosing statistically promising and/or provocative circumstances for the greatest likelihood of identifying new environmental risk factors for cancer.

Space-time clustering of Burkitt's lymphoma in East Africa: analysis of recent data and a new look at old data

Forty cases of Burkitts' lymphoma (BL) in North Mara, Tanzania, with onset between 1971 and 1977, were analysed for evidence of space-time clustering. Previous analyses in East Africa had produced conflicting results. The Knox method used in those analyses dichotomizes the space and time scales and does not take into account the degree of closeness. The Mantel method, a generalization of Knox's, does permit closeness between pairs of cases to enter into computations. To see whether this method could clarify matters, previously reported data sets from West Nile, Uganda and North Mara were reanalysed. Unexplained differences were found between West Nile and North Mara with respect to age, sex and temporal distributions of BL, and between the eastern and western parts of North Mara with respect to incidence. In West Nile between 1961 and 1965, there was clustering. All of the Mantel analyses and a few of the Knox analyses were highly significant (p less than 0.0025). Since 1966, evidence of clustering is weak. In North Mara, there was no statistical evidence of space-time clustering between 1971 and 1977, as there was none between 1964 and 1970. The conflicting results in East Africa are compatible with a model involving several factors which "move about", or with a single factor which is sporadic in some areas but constant in others. Alternatively, artifactual biases or coincidence may have created or wiped out the appearance of clustering. Results of space-time clustering analyses permit little discrimination between infectious and non-infectious etiologic hypotheses. Either one type or both may be operating.

Burkitt's lymphoma in Ghana: urban-rural distribution, time-space clustering and seasonality

Epidemiological data are summarized from 236 cases of Burkitt's lymphoma (greater than 90% cytologically or histologically confirmed) seen from 1970 through 1975 at Korle Bu Hospital, Accra, Ghana. The rate of referral from rural areas was greater than that from urban areas, despite a probable bias toward referral from urban areas. The distribution of cases in Ghana appeared to be non-random but we attribute this to variable access to medical care and physician interest. Rainfall did not appear to be an important factor. Seasonal variation and time-space clustering were not observed. The incidence here seems lower than that reported in East Africa. We found no evidence of an environmental influence with a short incubation period, as has been postulated for this disease in East Africa. The higher risk among rural patients is consistent with severe malaria being a factor in the etiology of Burkitt's lymphoma.

The seasonal variation of births of offspring from couples heterozygous for cystic fibrosis

To test whether the month of birth of patients with cystic fibrosis (CF) is seasonally distributed as reported in a Dutch survey, published Australian data were examined and no difference in the monthly variation was found between births of CF patients and their unaffected sibs. When the two groups were combined and analysed by periodic regression using successively higher Fourier terms, a significant fit to the observed frequencies was obtained with a bimodal curve. Possession of a single CF gene seems therefore sufficient for expression of the cyclic variation. In substantial agreement with the Dutch series, maximum frequencies were found to occur in March or April and in September. It is suggested that one or both parents may be subject to variable fertility mediated by a temperature-dependent mechanism. The relevance of a periodic fertility pattern in preserving the CF gene in the population by selective heterozygote advantage is discussed.

Epidemiological evidence for causal relationship between Epstein-Barr virus and Burkitt's lymphoma from Ugandan prospective study

Results from a prospective sero-epidemiological study initiated in Uganda in 1971 indicate that children with high antibody titres to Epstein-Barr virus structural antigens are at high risk of developing Burkitt's lymphoma. These findings strongly support a causal relationship between the Epstein-Barr virus and Burkitt's lymphoma but suggest that the oncogenic potential of the virus is realised only in exceptional circumstances.

Space-time clustering of Burkitt's lymphoma in the West Nile district of Uganda: 1961-1975

Epidemiological data relating to all 202 patients diagnosed with Burkitt's Lymphoma (BL) in the West Nile District of Uganda in the period 1961 to 1975 have been reviewed and analysed. Statistically significant evidence of space-time clustering of cases, first reported for the period 1961-65, was also present during 1972-73, but not during other periods. The patients involved in such clusters were found to be older than other patients (P less than 0.001). The average annual incidence of BL in the District was 2.45 x 10(-5) and overall there was no change in the incidence during the study period. However, there were statistically significant changes in incidence in different counties, which could not be explained as case-ascertainment artifacts. One sib pair of patients with BL was found and the series also included 7 instances of BL in two cousins. It is suggested that study of variation in the intensity and type of malarial infestation in different areas at different times may help explain the epidemiological findings and suggest what, if any, aspects of this infection are critical for inducing BL.

Further studies of space-time clustering of Burkitt's lymphoma in Uganda

All hospital-treated cases of Burkitt's lymphoma (BL), with onset of symptoms in the period 1963-68 and resident in the Lango and Acholi districts of Uganda, were identified. The average annual incidence of BL in the 6-year period was 1-87 X 10(-5), similar to that in the adjacent West Nile district. Contrary to findings in other areas of Uganda, there was no evidence of seasonal variation in the onset of cases, nor of space-time clustering, nor of a decline in the incidence of BL in the study period. An inverse relationship was noted between the median age at onset of BL and the incidence of the disease in different areas of Uganda, a finding consistent with intense malarial infection being a precipitating factor for BL. The variable observations with respect to space-time clustering of BL and seasonal variation in incidence in different areas remains unexplained, but it is suggested that a closer study of the patterns of malarial infection in these areas may help to account for the findings.

Primary intracranial Burkitt's lymphoma in an infant

A case of intracranial Burkitt's lymphoma is reported in a child whose symptoms began at 3 months of age with a definite histologic diagnosis established at 18 months. Serologic studies demonstrated high antibody titers to Epstein-Barr virus (EBV) in the patient and in four out of five members of the immediate family. The patient also demonstrated immunity to antigens derived from African Burkitt's lymphoma cell lines. The autopsy findings strongly support the case for the primary intracranial origin of the neoplasm and a perinatal infection with EBV is probable in this case.

Epidemiology of childhood leukaemia in greater london: A search for evidence of transmission assuming a possibly long latent period

Studies of space-time clustering of cases of childhood leukaemia have yielded equivocal results. This might be because the disease has a long and variable latent period, in which case the usual statistical tests for such clustering are inappropriate. A new statistical method is described which allows for such latent periods. For each patient, periods of "susceptibility" and "infectivity" are defined in which it is assumed he respectively "caught" and could "transmit" the disease. The measure of clustering is taken as the number of patients who were in the "right" place at the "right" time to "catch" the disease from another patient. This test is applied to childhood acute lymphoblastic leukaemia (death before age 6) in Greater London in the period 1952-65. Cases are postulated to be "susceptible" at various times before clinical onset of leukaemia, including in utero, and "infective" at various times around onset. Their effective "contacts" at these times are defined as circles of radius up to 4 km around their places of residence at these times. Slight evidence of clustering was found associated with certain of the defined times and distances, but the degree of clustering was small and could reasonably be attributed to chance. It is suggested, however, that this method of analysis might usefully be applied to other sets of such data. No evidence was found to add to our previously reported finding of space-time clustering of the dates and places of birth of children with leukaemia.

Etiology of childhood bone cancer: epidemiologic observations

In dogs, osteosarcoma is markedly more frequent in giant breeds than in small ones. Ewing's tumor rarely occurs in species other than man. In children, both osteosarcoma dne Ewing's tumor appear to be related to the rate of bone growth. Nonradiogenic osteosarcoma occurs excessively in persons with the heritable form of retinoblastoma, and in certain malformation syndromes, some of which are known to be genetically induced. Osteosarcoma may also be of the heritable type when it is multicentric or aggregates in families. The neoplasm may occur excessively in certain families with specific cancers not involving bone. By contrast, the only evidence of a genetic influence on Ewing's tumor is its near-absence among blacks in the United States and in Africa. The only exogenous agent known to induce osteosarcoma (but not Ewing's tumor) in man is ionizing radiation in substantial doses. There is no epidemiologic evidence for the virus etiology of bone cancer in man. Despite the epidemiologic differences between osteosarcoma and Ewing's tumor, both histologic types occasionally occur in different portions of the same neoplasm.

Crohn's disease in Nottingham: a search for time-space clustering

All cases of Crohn's disease in the Nottingham area were ascertained and the date and place of domicile and work at the time of onset of symptoms noted. Applying the Knox and Pike and Smith tests for clustering of patients in time and space, no significant results were observed. Further analysis of differences in time-space clustering between a group of patients and matched controls is in hand.

Burkitt's lymphoma: a time-space cluster of cases in Bwamba County of Uganda

Seven cases of Burkitt's lymphoma have to date (March 1971) been diagnosed in the county of Bwamba in Uganda. All these patients had the clinical onset of their tumour in the 27 months from October 1966 to December 1968; five of them in the last six months of this period. Two of the patients were full sibs living in the same house. This is the most discrete time-space cluster of the disease yet recorded and provides further evidence for a role in the aetiology of Burkitt's lymphoma of an infective agent with a relatively short latent period.

Burkitt's lymphoma in Ilesha, Western Nigeria

The clinical picture and local epidemiology in 65 cases of Burkitt's lymphoma seen in Ilesha, Western Nigeria, over a 16-year period is presented. Incidence figures have been calculated and comparison made with other Nigerian and East African reports. Ilesha is the centre of a high tumour density area. A changing pattern of presentation over the years has evolved. Its possible relationship to the treatment of malaria and immunization facilities is suggested and discussed.

A comparison of results achieved in treating two series of patients with Burkitt's lymphoma

The results of treating two series of patients with Burkitt's lymphoma are presented in the form of survival curves. The second series shows an improved survival rate which seems to be due to a potentiating effect by potassium iodide on oral cyclophosphamide. So far no reason for this effect has been found.

Burkitt's lymphoma: remissions following seemingly non-specific therapy

Long-term remissions observed in four out of eight unselected patients with Burkitt's lymphoma following seemingly non-specific treatment with Septicemine, are described. This is regarded as strong evidence of an effective immunological response.

The Role of Epidemiological Investigation in the Detection of Environmental Carcinogenic Risks

An introductory review is presented of the uses and limitations of epidemiological methods for investigating cancer etiology. Uses of epidemiological methods can be grouped under three main headings: search af etiological indications, test of etiological hypotheses, and assessment of the effect of large scale prophylactic or therapeutic treatments. The search of etiological indications is chiefly performed through an analysis of mortality and/or morbidity data: time and space distribution of cancers are usually studied and sometimes an investigation on time-space association is added. On this basis etiological hypotheses are formulated and tested using retrospective studies and/or prospective studies: typical examples of these are found in oncological literature. Assessment of the effect of large scale prophylactic or therapeutic treatments, where feasible, is a further check on the soundness of an etiological hypothesis. Limitations intrinsic to the epidemiological approach (as to any merely observational approach) can be partly overcome through close linkage between epidemiologic and experimental oncology; use of mathematical models to interpret on a common basis data from epidemiological and laboratory studies can make easier this task.