Chapter 4: Cancer incidence in Canada: trends and projections (1983-2032) – Central nervous system cancers - HPCDP: Volume 35, Supplement 1, Spring 2015

Chapter 4: Projections by Cancer Site

18. Central nervous system cancers

Cancers of the brain and nervous system are referred to collectively as central nervous system (CNS) cancers. During 2003–2007, the average annual number of CNS cancers was 1365 for males and 1055 for females in Canada, making up 1.7% and 1.4% of all new male and female cancer cases, respectively (Tables 4.18.1 and 4.18.2). One in 117 Canadian males and 1 in 150 females can expect to be diagnosed with CNS cancers in their lifetime, and 1 in 165 males and 1 in 220 females are likely to die from it.^{Endnote 1}

CNS cancers have a bimodal age distribution, with one peak in the pediatric population and another, much larger, in people in their 70s. In 2003–2007, the agespecific incidence was higher during early childhood (0–4 years) than young adulthood, increased gradually to peak at age 75 to 79, and then decreased (Figure 4.18.1).

CNS cancer is the second most common childhood malignancy (after leukemia), representing 20% of all cancers diagnosed in 0 to 14 year olds.^{Endnote 254} CNS cancers are the most common cause of cancer death in children. In 2003–2007, nearly 60% of CNS cancers were diagnosed in people aged 55 and over (Tables 4.18.1 and 4.18.2). Males and females had similar rates up to their late 30s, after which the rates were higher in males and the divergence increased consistently with age (Figure 4.18.1). The 5-year relative survival rates for CNS cancers diagnosed between 2006 and 2008 were 23% for males and 28% for females.^{Endnote 1} Survival is significantly higher in children and younger adults.^{Endnote 36, Endnote 254}

The overall incidence rates of CNS cancers in males have decreased consistently since 1988–1992, but to a very small degree, while the rates in females were relatively stable until 1998–2002 and then decreased slightly (Figure 4.18.2). During 1998–2007, ASIRs of CNS cancer were stable: decreased in males by 0.4% per year and by 0.8% in females (Figures 3.1 and 3.2). When the Atlantic region is excluded, an east–west gradient in ASIRs appears in both sexes starting from 1993–1997, with the highest rates in Quebec and the lowest rates in British Columbia (Figure 4.18.2). The ASIRs in the Atlantic region, which had been in the lower regional rates, approached the national level in the last observation period (2003–2007).

We based the CNS cancer projections on the trends in all the observation quinquennia. This produced downward trends in the predicted rates in males in Canada and its regions, decreasing by 4% in Quebec and 9% to 20% in the other regions from 2003–2007 to 2028–2032 (Figure 4.18.2). For females, the rates are expected to be stable in Quebec and the Atlantic region, and to decrease by 8% to 13% in the other regions. For both males and females, Quebec and British Columbia will remain in their respective highest and lowest ranking in the regional rates. The overall age-specific ASIRs are expected to stabilize in the youngest age group and decrease in each of the other age groups (Figure 4.18.3).

From 2003–2007 to 2028–2032, the ASIRs of CNS cancers are expected to decrease by 10% in males, from 7.9 to 7.1 per 100 000, and decrease by 8% in females, from 5.6 to 5.2 per 100 000 (Tables 4.18.3 and 4.18.4). Nevertheless, the aging and growth of the population means that the annual number of male cases is projected to rise by 44%, from 1365 to 1965, and the number of female cases, by 40%, from 1055 to 1470 (Tables 4.18.1 and 4.18.2).

Comments

Investigators have suggested that the increase in CNS cancer rates in people aged 75 or older in the observed periods until 1998–2002 was due to improved diagnostic techniques.^{Endnote 255} X-radiation and gamma-radiation are the only established risk factors for CNS cancers, according to IARC.^{Endnote 47} This conclusion was mainly based on studies of atomic bomb survivors and of patients with radiation diagnosis and treatment. IARC classifies radiofrequency non-ionizing radiation from telecommunications as a possible cause of CNS cancers, with limited evidence.^{Endnote 47, Endnote 86} Genetic and hereditary conditions are also linked to an increased risk. Having a parent with the disease confers a 1.7-fold increased risk, and having an affected sibling doubles the risk.^{Endnote 256}