Survival from brain tumours in England and Wales up to 2001.

Abstract

Brain tumours comprise 2% of all malignant neoplasms in adults in England and Wales, with some 4000 new cases and 3000 deaths each year. Incidence has increased by approximately 25% since 1971 in England and Wales (Quinn et al, 2001). Similar increases have been seen in other western countries (Muir et al, 1994). Brain tumours are 20–50% more common in men. Incidence was approximately 25% higher in the most affluent fifth of the population in England and Wales than in the most deprived fifth during 1991–1993 (Quinn et al, 2001). The cause of most brain tumours is unknown. Ionising radiation is the only established cause, although some nitrosamines may be a risk factor (Preston-Martin, 1996). Inherited syndromes may account for 5% of cases. Acquired immunosuppression may increase the risk of cerebral lymphoma. Occupations that have been linked to increased risk include the petrochemical and rubber industries, agricultural work, the nuclear industry and work involving exposure to electromagnetic fields (Preston-Martin et al, 2006). Only tumours of the brain explicitly coded as primary, malignant (behaviour code 3) tumours were included here. Patients previously registered with another primary malignancy at any time since 1971 were excluded. Brain tumours coded as benign (behaviour code 0) or of uncertain or unspecified behaviour (behaviour code 1) are often considered together with malignant tumours (Muir et al, 1994), and approximately 10 900 such brain tumours were recorded in the National Cancer Registry during the period 1986–1999, approximately 20% of all recorded brain tumours in all regions of England and Wales (data not shown). These tumours were not considered eligible for analysis. It can be difficult to distinguish primary tumours of the brain from metastases of primary tumours in other organs, which are common, but tumours coded as metastatic (behaviour code 6) were excluded. Malignant tumours of the cranial nerves and spinal cord were also excluded. The survival analyses reported here are based on the data for 37 917 adults (aged 15–99 years) who were registered with a first, primary, malignant tumour of the brain in England and Wales during the period 1986–1999 and followed up to the end of 2001. These patients represented approximately 86% of those eligible for analysis. For 1.9%, the vital status was unknown on 5 November 2002 when the data were extracted for analysis, and they were excluded. Patients whose brain tumour was not their first primary malignancy (1.8%) were also excluded. Most of the other exclusions were for a recorded survival time of zero (date of diagnosis same as date of death; 9.8% of cases). Some of these patients may have died on the day of diagnosis, but many are likely to have been registered from a death certificate only (DCO) (data not shown), and the two groups could not be distinguished in these data. As the date of diagnosis and thus the duration of survival are not available from a death certificate, both categories were excluded. Such patients may well have shorter than average survival (Berrino et al, 1995); hence, their exclusion may have caused slight overestimation of overall survival. However, the proportion of DCO cases was similar between deprivation groups and stable over time; hence, their exclusion is unlikely to have caused bias in the estimates of trends in survival, or of socioeconomic gradients. During the 1990s, some 50% of brain tumours were specified as arising in the frontal, parietal, temporal or occipital lobes, and only 3% arose in the cerebellum or brain stem, but the site was poorly specified or unspecified for 42% of tumours. The proportions are similar to those for the 1980s (Coleman et al, 1999). Gliomas represented 87% of the tumours, mainly malignant glioma (52%) and astrocytoma (30%). Morphology was ill-defined or undefined for approximately 11%.