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

Abstract

Incidence patterns, trends, and spatial and/or temporal clustering of childhood brain tumors were analyzed in the population-based national cancer registry of Sweden. 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. 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=0.0001) and the astrocytoma subgroup (P=0.0001). The annual average increases were 2.6% (95% CI=1.5-3.8) and 3.0%, respectively (95% CI=1.6-4.4). The increase in astrocytoma cases was significantly larger for girls than for boys (P=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. 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.