Burkitt's lymphoma in the North Mara district of Tanzania 1964-70: failure to find evidence of time-space clustering in a high risk isolated rural area

Burkitt lymphoma risk shows geographic and temporal associations with Plasmodium falciparum infections in Uganda, Tanzania, and Kenya

Endemic Burkitt lymphoma (eBL) is a pediatric cancer coendemic with malaria in sub-Saharan Africa, suggesting an etiological link between them. However, previous cross-sectional studies of limited geographic areas have not found a convincing association. We used spatially detailed data from the Epidemiology of Burkitt Lymphoma in East African Children and Minors (EMBLEM) study to assess this relationship. EMBLEM is a case-control study of eBL from 2010 through 2016 in six regions of Kenya, Uganda, and Tanzania. To measure the intensity of exposure to the malaria parasite, Plasmodium falciparum, among children in these regions, we used high-resolution spatial data from the Malaria Atlas Project to estimate the annual number of P. falciparum infections from 2000 through 2016 for each of 49 districts within the study region. Cumulative P. falciparum exposure, calculated as the sum of annual infections by birth cohort, varied widely, with a median of 47 estimated infections per child by age 10, ranging from 4 to 315 infections. eBL incidence increased 39% for each 100 additional lifetime P. falciparum infections (95% CI: 6.10 to 81.04%) with the risk peaking among children aged 5 to 11 and declining thereafter. Alternative models using estimated annual P. falciparum infections 0 to 10 y before eBL onset were inconclusive, suggesting that eBL risk is a function of cumulative rather than recent cross-sectional exposure. Our findings provide population-level evidence that eBL is a phenotype related to heavy lifetime exposure to P. falciparum malaria and support emphasizing the link between malaria and eBL.

The burden of Burkitt lymphoma in Africa

BACKGROUND

Burkitt lymphoma (BL) is a relatively common cancer of childhood in tropical Africa, although its precise incidence and continent-wide geographic distribution have not been previously systematically studied.

METHODS

Using the methods employed to produce national estimates of cancer incidence for the "Globocan" series of the International Agency for Research on Cancer, along with detailed information on cancer incidence by histological subtype from cancer registries in Africa, we estimate the numbers and rates of incidence by sex, age group, country and region of Africa.

RESULTS

We estimate that the number of new cases that occurred in 2018 to be about 3900, two thirds in males, and 81% in children aged 0-14. On a national basis, the geographic distribution of incidence rates among children in sub-Saharan Africa resembles that of the prevalence of infection with Falciparum malaria. An estimated 81% of cases are associated with infection with Epstein Barr virus (EBV).

CONCLUSIONS

BL comprises almost 50% of childhood of non-Hodgkin lymphoma in Africa, almost all of which are associated with EBV, with the geographic distribution - at least in sub Saharan Africa - mediated by infection with malaria.

Burkitt lymphoma: Trends in children below 15 years reveal priority areas for early diagnosis activities in north-west Cameroon

Background: Burkitt lymphoma is one of the most common childhood cancers in Cameroon. Incidence rates of 5.9/100 000 and 2.58 per 100 000 have been reported in two studies in 2005 and 2012 amongst children below 15 years in the North-West Region.Aim: This study seeks to examine how Burkitt lymphoma incidence has varied between the various health districts of north-west Cameroon from 2003 to 2015.Setting: North-West region of Cameroon.Method: Ethics approval was obtained from the relevant university and Health Services Institutional Review Board. Population data was obtained from the regional delegation of public health. The Paediatric Oncology Networked Database registry from two hospitals and two pathology-based registries were reviewed for cases per year from the various districts. Age-standardised incidence rates were computed for all districts by year using the World Health Organizaion world standard populations.Results: A total of 317 cases were registered. Overall age-standardised incidence rate was 3.07 per 100 000. Annual incidence ranged from 0.09 in 2003 to 6.12 in 2010. The districts with the highest incidence rates for the entire study period include Nwa with 10.54; Ndop with 5.63; Benakuma with 5.48; Ako with 4.97; and Nkambe with 4.73.Conclusion: Clustering of Burkitt lymphoma is seen in the region, with the highest incidence in Nwa, Ndop, Benakuma, Ako and Nkambe. These districts should be prioritised for awareness creation campaigns. There is need for a population-based childhood cancer registry in the region, which will use both active and passive surveillance methods to record all childhood cancer cases.

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.

Epidemiology of Burkitt's lymphoma in Northwest Province, Cameroon, 2003-2010

BACKGROUND

Burkitt's lymphoma (BL) is an aggressive non-Hodgkin's lymphoma endemic to regions of Africa. Cases are thought to be typically found in low-lying, humid regions where malaria is rife.

AIMS AND OBJECTIVES

To investigate the clinical characteristics of BL, its incidence and relationship with malarial incidence in Northwest (NW) Province, Cameroon.

METHODS

Data on BL were collected from the three tertiary referral centres for BL treatment in NW Province, Cameroon. Data on malaria were collected from the Delegation of Public Health in Bamenda, NW Province. Data were collected between March and May 2010.

RESULTS

471 cases of BL were identified. The St Jude's stage of patients at presentation was as follows: stage I, 14.4% (43/299); stage II, 8.4% (25/299); stage III, 69.9% (209/299); stage IV, 7.4% (22/299). The incidences of BL per 100,000 children <15 years of age from 2005 to 2009 were as follows: 2005, 3.01 (29); 2006, 2.02 (20); 2007, 2.45 (25); 2008, 2.38 (25); 2009, 3.06 (33). The average incidence in NW Province was 2.58. In the Ndop plain, Ngo-Ketunjia, the incidences of BL were as follows: 2005, 10.3 (10); 2006, 3.00 (3); 2007, 1.95 (2); 2008, 2.84 (3); 2009, 4.60 (5). The average incidence was 4.54/100,000 children <15 years of age. Statistical analysis demonstrated a sinusoidal distribution of malaria cases throughout the year (P<0.00), with a peak incidence on 10 April. Conversely, no sinusoidal distribution of BL cases was demonstrated throughout the year (P = 0.09).

CONCLUSION

No relationship was demonstrated between an acute malarial infection and BL. Significant clustering was found, with the low-lying Ndop plain of Ngo-Ketunjia having an incidence of BL nearly twice that elsewhere in the region. The study demonstrates that the incidence of BL in NW Province, Cameroon remains one of the highest documented in the world.

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.

Familial Burkitt's lymphoma in Papua New Guinea

A study of Burkitt's lymphoma (BL) in Papua New Guinea for the years 1958-87 revealed four instances of familial BL. Incident cases occurred within 1 year of each other in the four families. Personal follow-up was possible for three of these families whose pedigrees showed that two or more siblings were affected. There was no significant variation of the incidence of BL by year of diagnosis or month of onset. There was significant variation in annual average incidence of BL between the three provinces studied, with the highest incidence in the Nuku and Lumi census districts (of the West Sepik Province). This is the first report of familial BL outside Africa.

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 markers in a series of Burkitt's lymphomas from the West Nile District, Uganda

In an epidemiological survey in the West Nile District of Uganda, 70 pathologically confirmed BL cases were detected over a 5-yr period; this corresponded to an annual incidence rate of 1.6 per 100,000 general population or about 5 per 100,000 children in the age group 5-14 yr. Of the confirmed cases which were examined by EBV/DNA molecular hybridization, 96% were found to contain an average of 38 EBV genome equivalents per tumour cell, whereas none of the examined unconfirmed cases did. Duplicate hybridization assays in two laboratories were in close agreement. Serological testing showed that 91% of the confirmed BL cases had elevated EBV/VCA titres (greater than or equal to 160) and 64% were EA(D)-positive (greater than or equal to 10). Most of the cases with high EBV/genome content had high VCA titres, but there was a poor correlation between the two parameters among all cases. This study confirms that in high BL incidence areas the association between EBV and this lymphoma is almost constant, whereas it is exceptional in low-incidence areas. This further supports the aetiological implication of EBV in the endemicity of this tumor in equatorial Africa.

Multiple cases of Burkitt's lymphoma and other neoplasms in families in the North Mara District of Tanzania

In an area of Tanzania in which Burkitt's lymphoma (BL) is endemic, five families are described in which multiple cases of BL were found or BL occurred with other neoplasms. The patients include two brothers and one half-brother with BL, two brothers with BL, a woman with nasopharyngeal carcinoma (NPC) whose daughter had BL, a boy with BL whose sister developed chronic myelogenous leukaemia (CML), and a man with CML whose son developed BL. The two full-sib pairs with BL is significantly more than would be expected to have arisen by chance and the association of BL with NPC and CML among close relatives is remarkable in view of the rarity of the last two neoplasms in the study area. It is suggested that genetic factors may be important. It is suggested that genetic factors may be important in determining susceptibility to the three malignancies in this population, but the possibility that the clustering of cases within families may be due to local environmental factors cannot be excluded.

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.

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.