Childhood leukaemia in The Netherlands, 1973-1986: temporary variation of the incidence of acute lymphocytic leukaemia in young children

Optimizing therapy in the modern age: differences in length of maintenance therapy in acute lymphoblastic leukemia

A majority of children and young adults with acute lymphoblastic leukemia (ALL) are cured with contemporary multiagent chemotherapy regimens. The high rate of survival is largely the result of 70 years of randomized clinical trials performed by international cooperative groups. Contemporary ALL therapy usually consists of cycles of multiagent chemotherapy administered over 2 to 3 years that includes central nervous system (CNS) prophylaxis, primarily consisting of CNS-penetrating systemic agents and intrathecal therapy. Although the treatment backbones vary among cooperative groups, the same agents are used, and the outcomes are comparable. ALL therapy typically begins with 5 to 9 months of more-intensive chemotherapy followed by a prolonged low-intensity maintenance phase. Historically, a few cooperative groups treated boys with 1 more year of maintenance therapy than girls; however, most groups treated boys and girls with equal therapy lengths. This practice arose because of inferior survival in boys with older less-intensive regimens. The extra year of therapy added significant burden to patients and families and involved short- and long-term risks that were potentially life threatening and debilitating. The Children's Oncology Group recently changed its approach as part of its current generation of trials in B-cell ALL and now treats boys and girls with the same duration of therapy. We discuss the rationale behind this change, review the data and differences in practice across cooperative groups, and provide our perspective regarding the length of maintenance therapy.

Radiation Exposure From Pediatric CT Scans and Subsequent Cancer Risk in the Netherlands

BACKGROUND

Computed tomography (CT), a strong diagnostic tool, delivers higher radiation doses than most imaging modalities. As CT use has increased rapidly, radiation protection is important, particularly among children. We evaluate leukemia and brain tumor risk following exposure to low-dose ionizing radiation from CT scans in childhood.

METHODS

For a nationwide retrospective cohort of 168 394 children who received one or more CT scans in a Dutch hospital between 1979 and 2012 who were younger than age 18 years, we obtained cancer incidence, vital status, and confounder information by record linkage with external registries. Standardized incidence ratios were calculated using cancer incidence rates from the general Dutch population. Excess relative risks (ERRs) per 100 mGy organ dose were calculated with Poisson regression. All statistical tests were two-sided.

RESULTS

Standardized incidence ratios were elevated for all cancer sites. Mean cumulative bone marrow doses were 9.5 mGy at the end of follow-up, and leukemia risk (excluding myelodysplastic syndrome) was not associated with cumulative bone marrow dose (44 cases). Cumulative brain dose was on average 38.5 mGy and was statistically significantly associated with risk for malignant and nonmalignant brain tumors combined (ERR/100 mGy: 0.86, 95% confidence interval = 0.20 to 2.22, P = .002, 84 cases). Excluding tuberous sclerosis complex patients did not substantially change the risk.

CONCLUSIONS

We found evidence that CT-related radiation exposure increases brain tumor risk. No association was observed for leukemia. Compared with the general population, incidence of brain tumors was higher in the cohort of children with CT scans, requiring cautious interpretation of the findings.

Incidence and survival time trends for Spanish children and adolescents with leukaemia from 1983 to 2007

OBJECTIVE

We have analysed incidence and survival trends of children and adolescents with leukaemia registered in Spanish population-based cancer registries during the period 1983-2007.

METHODS

Childhood and adolescent leukaemia cases were drawn from the 11 Spanish population-based cancer registries. For survival, registries with data for the period 1991-2005 and follow-up until 31-12-2010 were included. Overall incidence trends were evaluated using joinpoint analysis. Observed survival rates were estimated using Kaplan-Meier, and trends were tested using the log-rank test.

RESULTS

Based on 2606 cases (2274 children and 332 adolescents), the overall age-adjusted incidence rate (ASRw) of leukaemia was 47.9 cases per million child-years in children and 23.8 in adolescents. The ASRw of leukaemia increased with an annual percentage change of 9.6 % (95 % CI: 2.2-17.6) until 1990 followed by a stabilisation of rates. In adolescents, incidence did not increase. Five-year survival increased from 66 % in 1991-1995 to 76 % in 2001-2005. By age, survival was dramatically lower in infants (0) and adolescents (15-19) than in the other age groups and no improvement was observed. In both children and adolescents, differences in 5-year survival rates among major subgroups of leukaemias were significant.

CONCLUSIONS

The increasing incidence trends observed in childhood leukaemias during the study period were confined to the beginning of the period. Remarkable improvements in survival have been observed in Spanish children with leukaemias. However, this improvement was not observed in infants and adolescents.

Incidence of childhood leukemia in Yogyakarta, Indonesia, 1998-2009

BACKGROUND

In most developing countries, incidence data for childhood cancers are less reliable, because very few population-based registries exist. The aim of this study was to present the epidemiology of childhood leukemia in the Dr. Sardjito Hospital (DSH) region, which catchment area extends beyond the boundaries of the Yogyakarta Special Province (YSP).

PROCEDURE

Health records of children, 0-14 years of age, who were diagnosed with leukemia between January 1998 and December 2009, were reviewed. Diagnosis of leukemia was confirmed by morphological and histochemical examination of marrow samples.

RESULTS

The estimated average annual incidence rate (AAIR) of childhood acute leukemia in DSH was 46.2 per million per year. Interestingly, the annual incidence rate (AIR) of childhood acute leukemia from the catchment area of DSH significantly increased from 35 in 1999 to 70 in 2009 (ANOVA, P = 0.003). The YSP population data, analyzed separately, showed an increase in AIR from 15.7 to 32.9 (ANOVA, P = 0.325) and an AAIR of 28.8. Remarkably, a relatively high frequency (25.5% in DSH and 27.7% in YSP) of children with AML was found in the group of acute leukemias.

CONCLUSION

The DSH incidence calculations may be overestimated due to an underestimation of the population number. Since the population count for YSP is more precise, the data of YSP were used for comparison with developed countries. AAIR of ALL (20.8) is relatively low compared to Western countries (22.4-37.9). The AAIR of AML (8.0) is similar to Western countries (5.0-8.0) resulting a relatively high percentage of AML versus ALL (27.7%) in YSP.

Population-based incidence of childhood leukaemias and lymphomas in Spain (1993-2002)

The aim of this study was to estimate the incidence of leukaemias and lymphomas in children according to the International Classification of Childhood Cancer third edition (ICCC-3) in the population covered by the Girona, Valencia, and Zaragoza population-based cancer registries and compare it with the incidence rates in other European countries. All haematological malignancies (HMs) registered between 1993 and 2002 in children below 15 years of age were included in the study. Pathological and haematological diagnoses were reviewed, recoded according to International Classification of Diseases for Oncology-3 and reclassified on the basis of ICCC-3. Sex and age-adjusted incidence rates were calculated, using the world population as standard. Five hundred and seventy-one HMs were registered in the Girona, Valencia and Zaragoza Cancer Registries during the study period. According to ICCC-3, precursor cell leukaemias were the most frequent HMs in children and constituted 60% of all HMs (an age-adjusted incidence rate of 42.7 per million children-years). The second most frequent childhood HM was Hodgkin lymphoma (11.2% of all HMs), yielding an age-adjusted standardized incidence rate of 6.3 per million children-years. With regard to myeloid lineage, acute myeloid leukaemias were the most frequent with a rate of 7.9 per million children-years. The standardized incidence rates for lymphoid leukaemia (1.19) and Burkitt lymphoma (3.94) were statistically higher than the rates observed in Europe. Compared with European data, Spain has a high incidence of lymphoid leukaemias and lymphomas. In particular, a high incidence of Burkitt lymphoma was observed. The causes of this geographical variation are still unknown.

Temporal trends in the incidence rate of childhood cancer in Germany 1987-2004

The German Childhood Cancer Registry regularly presents graphs of childhood cancer incidence rates by period, but no systematic analysis. The Automated Childhood Cancer Information System-project found an increasing trend in Europe. Against this background we present the first detailed trend analysis of childhood (aged under 15) malignancies in Germany. We examined incidence rates separately in western Germany 1987-2004 and eastern Germany 1991-2004. We analyzed all malignancies, all main diagnostic groups and relevant subsets using an age-period-cohort model. Additionally we fitted fractional polynomials to assess the linearity of the drift. All malignancies combined (excluding Central Nervous System-tumors and neuroblastoma) show a significant trend: +0.7% in western and +1.1% per year in eastern Germany. The overall trend in Germany is mostly due to the significant increase in lymphoid leukemia, which increased significantly in western Germany (+0.7% per year) and significantly nonlinearly in eastern Germany (+3.3% per year until 1998, +0.8% since 1998), catching up from a level 20% below western Germany. This could be due to life style changes since the reunification in eastern Germany influencing early immune system training. We found no trends for acute non-lymphocytic leukemia and non-Hodgkin lymphoma. Hodgkin's disease shows a cohort effect in western Germany after reunification. Improved registration of CNS tumors led to an increase. Neuroblastoma yielded a period effect in western Germany due to screening. With the exception of germ cell tumors, further observations for solid tumor entities are in agreement with those reported for Europe.

Bayesian methods for early detection of changes in childhood cancer incidence: Trends for acute lymphoblastic leukaemia are consistent with an infectious aetiology

Published data on time trends in the incidence of childhood leukaemia show inconsistent patterns, with some studies showing increases and others showing relatively stable incidence rates. Data on time trends in childhood cancer incidence from the Childhood Cancer Registry of Piedmont, Italy were analysed using two different approaches: standard Poisson regression and a Bayesian regression approach including an autoregressive component. Our focus was on acute lymphoblastic leukaemia (ALL), since this is hypothesised to have an infectious aetiology, but for purposes of comparison we also conducted similar analyses for selected other childhood cancer sites (acute non-lymphoblastic leukaemia (AnLL), central nervous system (CNS) tumours and neuroblastoma (NB)). The two models fitted the data equally well, but led to different interpretations of the time trends. The first produced ever-increasing rates, while the latter produced non-monotonic patterns, particularly for ALL, which showed evidence of a cyclical pattern. The Bayesian analysis produced findings that are consistent with the hypothesis of an infectious aetiology for ALL, but not for AnLL or for solid tumours (CNS and NB). Although sudden changes in time trends should be interpreted with caution, the results of the Bayesian approach are consistent with current knowledge of the natural history of childhood ALL, including a short latency time and the postulated infectious aetiology of the disease.

Socioeconomic status and childhood leukaemia: a review

BACKGROUND

A long-held view links higher socioeconomic status (SES) to higher rates of childhood leukaemia. Some recent studies exhibit associations in the opposite direction.

METHODS

We reviewed journal literature through August 2002 for associations between childhood leukaemia and socioeconomic measures. We determined the direction of each association and its P-value. We described the results with regard to study design, calendar period, geographic locale, and level of the socioeconomic measures (individual or ecological). For measures with sufficient number of results, we computed summary P-values across studies.

RESULTS

Case-control studies conducted in North America since 1980 have involved subject interviews or self-administered questionnaires and have consistently reported inverse (negative) associations of childhood leukaemia with individual-level measures of family income, mother's education, and father's education. In contrast, associations have been consistently positive with father's occupational class in record-based case-control studies and with average occupational class in ecological studies.

CONCLUSIONS

Connections of SES measures to childhood leukaemia are likely to vary with place and time. Validation studies are needed to estimate SES-related selection and participation in case-control studies. Because different socioeconomic measures (such as income and education) and individual-level and ecological-level measures may represent different risk factors, we advise researchers to report these measures separately rather than in summary indices of social class.

Increasing incidence and improved survival of cancer in children and young adults in Southern Netherlands, 1973–1999

The aim of this study was to describe time trends in incidence, treatment and survival of children (0-14 years) and young adults (15-24 years) with cancer in an area in the Netherlands with a long registration period. Between 1973 and 1999, the population-based Eindhoven Cancer Registry (ECR) recorded 852 children and 1162 young adults with a malignancy and they were actively followed up until 1 July, 2003. The world standardised incidence rates for both children and young adults showed an increasing trend until 1997 and this flattened off afterwards (estimated annual percentage change [EAPC]=3.1%, P=0.66 for children and EAPC=3.6%, P=0.06 for young adults). Lymphomas in children and testicular malignancies and melanomas in young adults seemed to increase in particular. Better detection probably led to higher completeness for gliomas. Initial treatment for leukaemias and lymphomas in children has changed, protocols prescribe more chemotherapy and less radiotherapy. For all cancers combined, the 10-year survival rate for children significantly improved from 53% (95% confidence interval [95% CI] 45-61%) in 1973-1982 to 75% (95% CI 69-81%) in 1993-1999 (P-value<0.05). The 10-year survival rate for young adults significantly improved from 57% (95% CI 49-65%) to 81% (95% CI 77-85%) (P-value<0.05). We demonstrated significantly higher five-year survival rates for children with Hodgkin's disease (HD) and young adults with HD, non-seminoma or melanoma diagnosed in 1993-1999.

Incidence of childhood leukaemia and non-Hodgkinʼs lymphoma in France: National Registry of Childhood Leukaemia and Lymphoma, 1990–1999

The French National Registry of Childhood Leukaemia and Lymphoma (NRCL) covers the whole French mainland population aged less than 15 years (approximately 11 million children) for all childhood haematopoietic tumours since 1 January 1990, except Hodgkin's disease, which has been registered since 1 January 1999. During the period from 1990 to 1999, 5757 cases of leukaemia, lymphoma and myelodysplastic syndrome were registered in the NRCL, with an average of 2.5 sources per case. The age-standardized incidence rates per million per year were 43.1 for leukaemia (34.3 for acute lymphoblastic leukaemia, 7.1 for acute myeloblastic leukaemia, 0.6 for chronic myeloid leukaemia and 0.5 for chronic myelomonocytic leukaemia), 8.9 for non-Hodgkin's lymphomas and 6.7 for Hodgkin's disease. Down's syndrome was present in 110 cases of acute leukaemia (2.5%) and three cases of non-Hodgkin's lymphoma (0.3%). The incidence of acute lymphoblastic leukaemia showed a typical peak at age 2 years for girls and 3 years for boys. The incidence rates of leukaemia and non-Hodgkin's lymphoma did not show any temporal trends over the 10 year period.

Age- and Sex-Specific Incidence of Childhood Leukemia by Immunophenotype in the Nordic Countries

BACKGROUND

Studies from various countries have found an increasing incidence of childhood leukemia in recent decades. To characterize time trends in the age- and sex-specific incidence of childhood acute leukemia during the last 20 years in the Nordic countries, we analyzed a large set of population-based data from the Nordic Society of Paediatric Haematology and Oncology (NOPHO) in their acute leukemia database covering a population of approximately 5 million children aged 0-14 years.

METHODS

Temporal trends in acute myeloid leukemia and acute lymphoblastic leukemia incidence rates overall and for acute lymphoblastic leukemia immunophenotypes and for specific age groups were analyzed by Poisson regression adjusting for age, sex, and country. All statistical tests were two-sided.

RESULTS

We identified 1595 girls and 1859 boys diagnosed with acute lymphoblastic leukemia between January 1, 1982, and December 31, 2001, and 260 girls and 224 boys diagnosed with de novo acute myeloid leukemia between January 1, 1985, and December 31, 2001. No statistically significant change was seen in the overall incidence rate for acute lymphoblastic leukemia during the 20-year study (annual change = 0.22%, 95% confidence interval [CI] = -0.36% to 0.80%). The incidence rate of B-precursor acute lymphoblastic leukemia remained unchanged (annual change = 0.30%, 95% CI = -0.57% to 1.18%) from January 1, 1986, through December 31, 2001. A somewhat lower incidence in the first years of the study period indicated an early increasing incidence of B-precursor acute lymphoblastic leukemia that corresponded to a simultaneous decreasing incidence of unclassified acute lymphoblastic leukemia. Incidences of T-cell acute lymphoblastic leukemia (annual change = 1.55%, 95% CI = -1.14% to 4.31%) and acute myeloid leukemia (annual change = 0.58%, 95% CI = -1.24% to 2.44%) were stable during the study period.

CONCLUSION

Incidences of acute myeloid leukemia overall, acute lymphoblastic leukemia overall, and specific acute lymphoblastic leukemia immunophenotypes have been stable in the Nordic countries over the past two decades.

Increasing incidence of childhood leukemia in Northwest Italy, 1975-98

Although some childhood cancer registries reported increasing incidence, the evidence and magnitude of time trends in the incidence of childhood leukemia are debated and the scientific evidence is conflicting. Only limited data have so far been supplied from Southern European countries. We present an analysis of the incidence trend of childhood leukemia in Piedmont (NW Italy) in 1975-98, based on data from the population-based childhood cancer registry. The Childhood Cancer Registry of Piedmont has been recording cases of childhood neoplasms since 1967. Procedures have been uniform and are based on an active search for cases and relevant information. Only cases with confirmed residence in Piedmont at diagnosis are included. Eight hundred cases of leukemia (622 acute lymphoblastic [ALL], 133 acute nonlymphoblastic [AnLL], 45 other and unspecified) were recorded in the period 1975-98 considered in our study. Incidence trends were analyzed using piecewise regression and Poisson regression, based on annual incidence rates. As results from the 2 analyses were similar, only the former were reported. In the age group 1-4 years, a statistically significant annual 2.6% increase in incidence rate of ALL (adjusted by age and gender; 95% confidence interval [CI] 1.13-4.13) was estimated. There was no evidence of increase in other age groups. During 1980-98, a statistically significant 4.4% annual increase (95% CI 1.86-6.90) was seen for pre-B-All in the age group 1-4 years. An increase was also seen for T-ALL that was not statistically significant. Sensitivity analyses were conducted, with no relevant differences from the main results. Our data suggest an increasing trend in ALL incidence for children between the ages of 1 and 4 years. These results are unlikely to be explained by changes in quality of data or exhaustiveness in reporting in the study period. The results were not changed in the sensitivity analyses we conducted. Possible causes to be investigated include environmental factors, changes in family size and parental age, socioeconomic conditions and geographical distribution of cases.

Epidemiologic studies in a population-based childhood cancer registry in Northeast Hungary

BACKGROUND

Reports on the patterns of childhood cancer incidence are rare in Eastern Europe. To compare incidence rates and trends with international data, we processed records of the regional childhood cancer registry of Northeast Hungary.

PROCEDURE

Our computerized database contains population-based information on childhood cancer cases (<15 years) diagnosed in residents of two counties of Hungary: leukaemias from 1973, non-CNS solid tumours from 1978, and CNS tumours from 1984. After a retrospective evaluation of completeness of ascertainment, descriptive epidemiologic analyses were performed for the years of operation of the registry. Age-standardized annual incidence rates and age-specific incidences were calculated. Trends were evaluated in linear regression analysis.

RESULTS

The distribution of major histologic groups was similar to those observed in the Western countries with the exception that central nervous system tumours account for a higher percentage (27.3%). Average age-standardized annual incidence rates were as follows: all types of cancer: 120.7 per million; leukaemia: 37.3; CNS tumours: 31.6; lymphomas: 12.2; sympathetic nervous system tumours: 12.5; kidney tumours: 8.8. Significant increases were observed in incidence of leukaemia (average annual percent change AAPC: 0.7%), acute lymphoblastic leukaemia (AAPC: 1.9%), and all cancer groups (AAPC: 2.6%), but not in acute non-lymphocytic leukaemia or in CNS tumours. The strongest increases in cancer incidence were detected in the age group of 10-14 years (AAPC: 4.4%) and in infants (AAPC: 12.9%).

CONCLUSIONS

Incidences and trends are in accordance with the data in the latest literature, however, the contribution of CNS tumours and the rate of increase in total cancer incidence proved to be higher. Further detailed genetic and environmental studies of cancer registries may shed light on the etiology of the observed differences whether they represent a pattern specific for this region.

Incidence of childhood acute lymphoblastic leukaemia in Yorkshire, UK

Between 1980 and 1998, in the north-west of England, a significant rise in childhood acute lymphoblastic leukaemia was caused by an increase in the precursor B-cell form of this disease. We analysed data on children who were diagnosed with leukaemia in Yorkshire, UK, between 1974 and 1997. The incidence of acute lymphoblastic leukaemia remained stable, although a non-significant yearly increase of 2.4% was noted for the precursor B-cell form of this disease from 1980 onwards. The precursor B-cell form accounted for 80% of all acute lymphoblastic leukaemia. Our data are not consistent with increasing incidence for precursor B-cell acute lymphoblastic leukaemia, although numbers of children with acute myeloid leukaemia are rising.

Common and emerging infectious causes of hematological malignancies in the young

Comparative epidemiological studies have for a long time suggested a link (or links) between infectious agents and hematological malignancies in the young. Identification of Epstein-Barr virus (EBV) as the major cause of specific subtypes of Burkitt's lymphoma and Hodgkin's disease 20 and 10 years ago, respectively, and the recent involvement of human T-cell leukemia virus in non-Hodgkin's lymphomas of the T-cell lineage in young adults in Jamaica have given further credit to early presumptions that these diseases have an infectious etiology. The spectrum of possibly involved viruses: old, EBV, and new, herpesviruses 6, 7 and 8, and unknown retroviruses - as well as the list of partially or totally unresolved disease entities: Hodgkin's disease in adolescents, non-Hodgkin's lymphomas in the immunocompromised, and acute lymphocytic leukemia - is rapidly expanding. Both direct and indirect transforming effects of the above-mentioned viruses are being rapidly disclosed. However, the complex interaction between the different viruses and other causes of hematological malignancies in the young guarantees that many things remain to be discovered also in the future.

Epidemiology of childhood leukemia in Hokkaido, Japan

The population-based epidemiological indices (crude incidence, survival rate, mortality, etc.) of childhood leukemia (0-14 years of age) from 1969 to 1993 in Hokkaido Prefecture, Japan, were calculated, using data obtained from the Registry of Childhood Malignancies in Hokkaido Prefecture. A total of 1,084 cases of leukemia were diagnosed in the 1969-93 period. The annual incidence of all types of leukemia from 1984 to 1993 was about 4 per 100,000 children aged 0-14 years, with the incidence of ANLL decreasing slightly and that of ALL increasing. The ratio of ALL/ANLL could similarly be seen to be increasing in all age groups. Out of a cohort of 100,000 live births, about 65 children developed leukemia by 14 years of age, and in this longitudinal observation the ratio of ALL/ANLL was increasing. The incidence of ALL and ANLL and the ratio of ALL/ANLL in Japanese children are approaching those of Caucasians. Approximately 80% of the ALL cases were of the LI type (FAB classification), and about 65% of these could be immunologically classified as "common" ALL. The 5-year survival rate of T- and B-cell ALL cases was 50% or less, while that of "common" ALL cases was about 80%.

Childhood leukaemias in New Zealand: time trends and ethnic differences

Registrations from the New Zealand Cancer Registry were used to examine time trends in the incidence of leukaemias among children aged 0-14. There was a statistically significant increase in the incidence of leukaemia among children aged 0-4 during 1953-57 to 1988-90. In this age group, the recorded incidence rate increased from 4.89 per 100,000 person-years in 1953-57 to 7.92 in 1988-90. During 1973-77 to 1988-90 (and probably in earlier years), the increase was due to an increase in acute lymphoblastic leukaemia (ALL). The trends were unlikely to be due to changes in diagnosis or case ascertainment. The childhood leukaemia trends might be related to trends in family size, maternal age, socioeconomic level or exposure to infections. However, there are uncertainties about the importance of these factors or about their trends. The incidence of acute non-lymphoblastic leukaemia (ANLL) decreased between 1968-72 and 1988-90. The time trends highlight the likely importance of environmental factors in the aetiology of childhood leukaemias in New Zealand. The risk of ALL was lower in the Maori than in the non-Maori population (relative risk Maori/non-Maori 0.74). The risk of ANLL was higher among Maori (relative risk 1.84).

Small influence of parental educational level on the survival of children with leukaemia in The Netherlands between 1973 and 1979

We studied the effect of parental educational level (PEL), an indicator of socio-economic status (SES), on survival of children with acute lymphoblastic (ALL) and non-lymphoblastic leukaemia (ANLL). All children with ALL and ANLL diagnosed in The Netherlands in the period 1973-1979, registered by the Dutch Childhood Leukaemia Study Group and followed until 1991 were included. Bone marrow and blood smears had been uniformly classified in a central laboratory; cases with acute lymphoblastic leukaemia (ALL) were subdivided into standard risk (SR) and high risk (HR). PEL, assessed as a risk indicator in a separately conducted population-based case-control study of the same children (response rate: 88%), was divided into low, when neither of the parents had more than elementary school or lower vocational education, and high when either had more. Children with SR ALL of high PEL parents had a slightly higher 10-year survival rate than of low PEL parents (58% versus 54%, P = 0.25), whereas survival for the latter increased more (P = 0.06) from a lower level in the period 1973-1975. However, children of low PEL parents with HR ALL and ANLL had a higher 10-year survival rate compared with children of high PEL parents (P = 0.10 and 0.22, respectively). Children without information on PEL, non-responders, migrants and with missing values exhibited slightly worse survival rates. The influence of PEL on survival of acute leukaemia in children in The Netherlands during 1973-1979 appeared small or even equivocal. Small differences in SES and optimal geographic and financial access to care, delivered through national treatment protocols, may be responsible for these results.

Immunological subtypes of childhood acute lymphoblastic leukemia in Bulgaria

With regards to the geographical variation in acute lymphoblastic leukemia (ALL) distribution, we present data from the immunophenotyping of 171 newly diagnosed cases of childhood ALL in Bulgaria during a 4 year period (1990-1994). On the basis of 17 phenotypic markers the distribution of immunological subtypes was as follows: AUL 4%; Pro-B ALL 13%; common ALL 42%; Pre-B ALL 11%; B-ALL 1%; T-ALL 28% and unclassified 2%. Most of the cases were between 2 and 5 years of age. Common ALL was predominant (53%) in this age group. The male:female ratio was 1.7:1. The frequency of T-ALL (28%) was significantly higher (P < 0.01; t = 3.49) in comparison to that reported for the U.S.A. and West European countries (mean 13%). It was close to the frequency reported by some authors for France (20%), Greece (26%) and south Italy (28.1%). These countries and Bulgaria might form an environmental area with a moderate frequency of T-ALL.

Patterns and temporal trends in the incidence of malignant disease in children: I. Leukaemia and lymphoma

Patterns and trends in incidence of leukaemia and lymphoma in children aged under 15 years and resident in the North Western Regional Health Authority area of England at diagnosis, over the 35-year time period 1954-1988, were analysed. The study included 1407 cases registered with the Manchester Children's Tumour Registry, 100% of which had a histologically or cytologically verified diagnosis. Log-linear modelling identified significant linear increases in acute lymphocytic leukaemia (ALL) (average quinquennial increase 4%) and Hodgkin's disease (HD) (10%), but not in acute non-lymphocytic leukaemia nor non-Hodgkin's lymphoma. Additionally, the chi 2 test for trend identified a significant increase in the incidence of chronic myeloid leukaemia. The possibility that the increases seen in ALL and HD are linked to increases in prevalence of unknown infectious agents is discussed.

Malignant lymphomas in children in The Netherlands in the period 1973-1985: incidence in relation to leukemia: a report from the Dutch Childhood Leukemia Study Group

A retrospective study was done of the incidence of non-Hodgkin's lymphoma (NHL) in children in the Netherlands in the period 1973-85 in relation to that of acute lymphoblastic leukemia (ALL). Complete ascertainment of cases was most likely achieved through the network of cooperating pediatricians of the Dutch Childhood Leukemia Study Group (DCLSG). The incidence of NHL remained constant at 0.75 per 10(5) children per year; the boy/girl ratio was 2.5. In +/- 25% of cases the disease was localized at diagnosis. Of children with NHL who were not listed in the DCLSG leukemia register, 19% had greater than or equal to 25% lymphoblasts in the bone marrow at diagnosis, representing an overlap with ALL of +/- 5%. In 1% of the children with NHL an immuno-deficiency disorder preceded the diagnosis. The incidence of Hodgkin's disease (HD) was 0.3 per 10(5) children per year, with some fluctuation over time, the peak being 0.7 in 1983. The boy/girl ratio was 2.7. Age-specific incidence rates, clinical features of NHL and HD, as well as the ALL to NHL ratio corresponded with those in other European countries and for white children in the USA.