Increased incidence rates but no space–time clustering of childhood astrocytoma in Sweden, 1973–1992

Abstract

BACKGROUND.Incidence patterns, trends, and spatial and/or temporal clustering of childhood brain tumors were analyzed in the population-based national cancer registry of Sweden. METHODS.Temporal trends were analyzed by a logistic regression procedure in which the average annual percentages of change in incidence rates and the corresponding 95% confidence intervals (CIs) were calculated. Spatial and/or temporal clustering were investigated by using a geographic information system and analyzed with a modified version of the Knox test and a spatial scan statistic. RESULTS.Primary brain tumors in 1223 children ages 0 -15 years were registered during 1973-1992. In 80% of cases, the tumor was classified as malignant. Conclusive histopathology was classified in 1142 cases. The age-adjusted incidence rate for all subtypes of brain tumors was 35.9 cases per million children, and for malignant brain tumors 28.6. A statistically significant increasing temporal trend was observed for the group of malignant brain tumors as a whole (P ϭ 0.0001) and the astrocytoma subgroup (P ϭ 0.0001). The annual average increases were 2.6% (95% CI ϭ 1.5-3.8) and 3.0%, respectively (95% CI ϭ 1.6 -4.4). The increase in astrocytoma cases was significantly larger for girls than for boys (P ϭ 0.021) and was most striking for girls ages 6 -15 years, with an annual average increase of 4.7%.Rates had not increased for the primitive neuroectodermal tumor (PNET)/medulloblastoma or ependymoma subgroups. The geographic distribution of astrocytoma cases was homogenous. No statistically significant space-time interaction or local clusters in space and/or time were found for astrocytomas only or when astrocytomas were grouped with PNETs/medulloblastomas and ependymomas. CONCLUSIONS.The results show statistically increased incidence rates of childhood astroglial tumors, predominantly for girls, in Sweden during the period 1973-1992, but no clustering in space or time.

Increasing incidence of childhood tumours of the central nervous system in Denmark, 1980–1996

“…Overall, these findings agree with those of most previous studies (Blair and Birch, 1994;McKinney et al, 1994;Bunin et al, 1996;Gurney et al, 1996;Hjalmars et al, 1999;McNally et al, 2001;Dreifaldt et al, 2004), although differences have been found. Thus, a British study showed a stable rate of ependymomas (McNally et al, 2001), one study in the USA showed a stable rate of primitive neuroectodermal tumours (Gurney et al, 1996) and another study in the USA, spanning 21 years, showed that increases in the incidence rates of various morphological subgroups depends on the period studied .…”

“…Third, the greater increase in the incidence rate of slowly growing, benign tumours than of more aggressive tumours might indicate that heightened awareness of such tumours, improved diagnostic methods or improved access to diagnosis could explain the increase in childhood CNS tumour incidence, as these slowly growing tumours might otherwise have remained undetected, perhaps throughout life (Gurney et al, 1996;Smith et al, 1998). Accordingly, one Swedish study (Dreifaldt et al, 2004) also found a greater increase in the incidence rate of benign CNS tumours than of other types of CNS tumours, whereas another Swedish study (Hjalmars et al, 1999) found that the incidence rate increased to a greater extent for grade 3 -4 than for grade 1 -2 astrocytomas. We found the most pronounced increase in the annual incidence rate of slowly growing pilocytic astrocytomas, which have a good prognosis (Gjerris et al, 1998;Fernandez et al, 2003); however, the time between the onset of symptoms and diagnosis of pilocytic astrocytoma remained stable throughout the study, suggesting that earlier detection played only a minor role, if any.…”

“…Increasing incidence rates of central nervous system (CNS) tumours in children have been reported for several populations in countries where incident cancer cases are registered routinely, that is, in Australia, Italy, Sweden, the United Kingdom and the USA (Mosso et al, 1992;McKinney et al, 1994;Giles et al, 1995;Bunin et al, 1996;Gurney et al, 1996;Hjalmars et al, 1999;McNally et al, 2001;Dreifaldt et al, 2004). It is uncertain whether these increases are owing to improved diagnostic methods, changes in cancer registration procedures or changes in tumour classification practices, or whether the increases are biologically real and owing to changes in environmental or lifestyle factors (Black, 1998;Smith et al, 1998;Forman, 1999;Schechter, 1999;Varner, 1999).…”

“…In Sweden, the increase occurred throughout the 20-year period 1973 -1992 (Hjalmars et al, 1999), covering the introduction of both computed tomography (CT) and magnetic resonance imaging (MRI) as diagnostic methods. In contrast, the increase in the incidence rate of childhood CNS tumours in the United Kingdom occurred mostly before the introduction of MRI (McKinney et al, 1994;McNally et al, 2001).…”

Cancers in the first-degree relatives of children with brain tumours

“…About 80% of nervous system cancers are brain tumours, the incidence of which is highest in the Nordic countries being about 5 per 100 000 per year in Sweden Hjalmars et al, 1999). In spite of extensive studies, the causes of childhood brain cancer remain elusive, ionizing radiation and genetic predisposition being the only established risk factors (Bondy et al, 1991;Draper et al, 1994;Zahm and Devesa, 1995;Little et al, 1998;Little, 1999;Salminen et al, 1999;Kleihues and Cavenee, 2000).…”