Overall childhood cancer incidence
Around 1,500 children are diagnosed with cancer each year in the UK (Table 1.1).1-4
This equates to just under 140 cases per million children. The majority of childhood cancers aremalignant (93%), with the remainder being non-malignant tumours of the brain and central nervous system (CNS). In Great Britain, around one child in every 500 will develop some form of cancer by 14 years of age.5
Different types of childhood cancer have widely varying distributions of age at diagnosis, illustrated by age-specific incidence curves in Figure 1.1 and shown below 1.
The three most common types of cancer diagnosed in children are leukaemias; brain and CNS tumours and lymphomas collectively accounting for around two-thirds (66%) of all cancers diagnosed in 0-14 year olds (Figure 1.1).5
The incidence of cancer is about a fifth higher in boys than girls (ratio of around 1.2 : 1.0), and in both sexes the highest overall rates occur in the under fives, though this pattern varies greatly by tumour type (Figure 1.2).5
Leukaemias form the most commonly diagnosed cancer in children, accounting for around a third (31%) of all cases.15 Incidence peaks in boys and girls at the ages of three and two years, respectively, and subsequently decreases with age thereafter.
Acute lymphoblastic leukaemia (ALL) is the most common type of childhood leukaemia by far. ALL accounts for around four-fifths (79%) of all leukaemias diagnosed in children,5 and as such largely determines the age and sex pattern for childhood leukaemias overall. The incidence of ALL is much lower in adults, with children accounting for just over one-half (52%) of the total number of ALL cases being diagnosed at any age. 1
The next most common leukaemia diagnosed in children is acute myeloid leukaemia. AML accounts for 15% of childhood leukaemias; incidence rates are highest in infants (under one-year-olds) and show little variation with age from the age of three onwards (Figure 1.2).5
Read more about leukaemia for all ages
Brain and Central Nervous System (CNS) tumours (both malignant and non-malignant) form the second most common group of cancers in children, accounting for a quarter of all childhood cancers overall.5
The largest subgroup is astrocytoma and these constitute over two-fifths (43%) of all brain and CNS tumours in children.10 Astrocytoma is diagnosed throughout childhood and there is no strong pattern by either sex or age (Figure 1.3). Around three-quarters (76%) of astrocytomas are diagnosed as‘low grade’ and 15% as ‘high grade’.
The second most frequent subgroup is the intracranial and intraspinal embryonal tumours, which account for around a fifth (19%) of all childhood brain and CNS tumours. Most of this subgroup are primitive neuroectodermal tumours (PNETs), with nearly three-quarters (73%) being medulloblastoma. PNETs occur most frequently in younger children and incidence decreases with age (Figure 1.3).
Ten per cent of childhood brain and CNS tumours are defined as ependymoma and choroid plexus tumours; incidence is highest in one-year-olds in this subgroup (Figure 1.3).
Read more about brain and CNS tumours for all ages
Lymphomas account for a tenth of all cancers diagnosed in children and incidence is more than twice as high in boys than girls (ratio of around 2.2 : 1.0).5,15 Lymphomas are rare before the age of two and incidence increases with age thereafter such that lymphomas account for nearly a fifth (19%) of all childhood cancers diagnosed in 10-14 year-olds.15
There are two main types of lymphoma: Hodgkin lymphoma (also called Hodgkin’s disease) and non-Hodgkin lymphoma (NHL). Hodgkin lymphoma accounts for around two-fifths (41%) of all lymphomas diagnosed in children.5
Incidence increases steadily after the age of two until the last few years of childhood, where there is a much sharper increase such that two-thirds of all childhood Hodgkin lymphomas are diagnosed in 10–14 year-olds (Figure 1.4).
NHL (excluding Burkitt lymphoma) accounts for 44% of lymphomas in children. Incidence of NHL increases sharply in the first few years of childhood and subsequently increases more gradually with age (Figure 1.4).5
Read more about Hodgkin lymphoma and non-Hodgkin lymphoma for all ages.
The wide-ranging group of soft tissue sarcomas accounts for 7% of all childhood cancers overall.11Incidence is similar in both sexes in early and late childhood, but is markedly higher in boys between the ages of three and eight.
Just over half (53%) of all soft tissue sarcomas are rhabdomyosarcoma, which can occur in almost all parts of the body.5 The incidence of rhabdomyosarcoma is highest in three-year-olds (Figure 1.5).
Ewing and Askin tumours of soft tissue and peripheral primitive neuroectodermal tumours (pPNETs) of soft tissue collectively account for 15% of all soft tissue sarcomas. These tumours mainly occur in the trunk (62%), with the remainder being evenly divided between the head and neck and the limbs. Incidence remains fairly constant throughout most of childhood, with just a small increase in the last few years (Figure 1.5).5
Around 4% of childhood cancers are malignant tumours of the bone.5 Incidence rates are very similar in both sexes and increase steadily with age.
Overall, malignant bone tumours account for a tenth (9%) of all cancers diagnosed in 10-14 year-olds.5 The most common types of malignant bone tumours are osteosarcoma (accounting for 55% of cases) and Ewing tumour and related bone sarcomas (39% of cases).5
Osteosarcoma is extremely rare under the age of three; incidence increases with age thereafter such that over two-thirds (70%) of osteosarcomas are diagnosed in 10-14 year-olds (Figure 1.5 above). The vast majority of osteosarcomas are diagnosed in the long bones of the legs (84%) and arms (12%).
Ewing tumour and related bone sarcomas are mainly peripheral primitive neuroectodermal tumours (pPNETs) of the bone. Tumours can occur at a variety of sites, the most common being the long bones of the legs (38%) and the pelvis (23%).
Incidence of these tumours peaks in the last few years of childhood, with a male excess in 10-14 year-olds.5
Read more about bone cancer for all ages
This broad group of childhood tumours crosses over the standard classification, because embryonal tumours occur in many different parts of the body. There are four principal types – neuroblastoma in the sympathetic nervous system, retinoblastoma in the eye, nephroblastoma (Wilms tumour) in the kidney and hepatoblastoma in the liver. Other embryonal tumours include medulloblastoma in the brain and embryonal rhabdomyosarcoma in soft tissue.
They are characterised by the proliferation of tissue that is normally seen only in the developing embryo. They are generally very rare after childhood, and occur most commonly in the first few years of life (Figure 1.6). Several types of embryonal tumour have a peak of incidence in the first year of life. Some types are occasionally found to be present at birth.
Around 6% of childhood cancers are renal tumours and nephroblastoma (Wilms tumour) accounts for 90% of these.5 It is slightly different to the other principal embryonal tumours in that incidence rates have a slightly later peak in one- to three-year-olds (Figure 1.6 above). The majority (90%) of nephroblastomas occur in one kidney only.5
Read more about kidney cancer for all ages
Tumours of the sympathetic nervous system (SNS) account for 6% of childhood cancers overall, and nearly all tumours of the SNS are neuroblastomas (including ganglioneuroblastomas). Neuroblastoma is one of the principal embryonal tumours and is the most frequently occurring solid tumour in infants under the age of one, accounting for around a fifth (19%) of all cancers diagnosed in this age group.5 The incidence of neuroblastoma is rare after the age of five (Figure 1.6 above). Almost one half (46%) of neuroblastomas develop in the adrenal gland; other abdominal primary sites account for just over one quarter (26%) of cases, and thoracic sites account for 13%.
Retinoblastoma is another principal embryonal tumour and accounts for 3% of all cancers diagnosed in children.5 Around two-fifths (42%) of cases are diagnosed in the first year of life and incidence rates drop to a very low rate after five years of age (Figure 1.6 above). Around two-thirds (63%) of retinoblastomas are diagnosed in one eye only.5
Tumours of the liver are quite rare in childhood, with around one child in every million being diagnosed with the condition every year.5 This group is broadly divided into hepatoblastoma (Figure 1.6) and hepatic carcinomas, which account for around four-fifths (81%) and one-fifth (18%) of cases, respectively. Hepatoblastomas are the rarest of the four principal embryonal tumours, and are most likely to be diagnosed in children under two years of age.5
Read more about liver cancer for all ages
Carcinomas and melanomas account for 3% of childhood cancers overall. The group consists of carcinomas other than those of the kidney, liver and gonads that have already been mentioned, and malignant melanomas. Malignant melanomas account for around one-third (32%) of carcinomas and melanomas, and carcinomas of the skin and thyroid account for 17% and 15%, respectively.5
Germ cell and gonadal tumours account for 3% of all childhood cancers.5 The pattern by age and sex varies greatly by tumour type.
Malignant gonadal germ cell tumours account for 42% of this group; male gonadal germ cell tumours are most likely to be diagnosed in children less than two years old, with incidence rising again in teenagers, whereas incidence of female gonadal tumours increases with age. Tumours originating within the brain and spine account for more than a third (34%) of all gonadal and germ cell tumours, and are more common in older children (Figure 1.7). Other tumours in this group include extracranial and extragonadal germ cell tumours.5
Two large publications by the International Agency for Research on Cancer (IARC) in the 1980s and 1990s showed substantial variations in childhood cancer incidence between different regions of the world.16 For all childhood cancers diagnosed in the period 1980-1994, the World age-standardised incidence rates were typically in the range 70-160 cases per million children. 17 The UK incidence rate was at the lower end of the range observed in westernised countries, and Oceania and the white populations of North America were at the highest. More recent analyses of childhood cancer incidence in Australia and the US have shown continued high rates in comparison to the rest of the world.10
In Europe, the Automated Childhood Cancer Information System (ACCIS) 2 has enabled a detailed analysis of childhood cancer incidence across the continent.7 In the period 1988-1997, childhood cancer incidence rates were highest in Northern Europe and lowest in the British Isles/UK (Figure 1.8). Of the 19 countries studied, incidence rates were lowest in Turkey, Hungary and the UK and highest in Finland, Italy and Denmark. All of the diagnostic groups showed significant differences across Europe; brain and CNS tumours had the greatest variation in incidence, though differences in registration practice for non-malignant brain and CNS tumours could have accounted for some of the variation.7
Within the UK, there is limited evidence of geographical variation in incidence,6 though detailed analysis by tumour type is difficult due to the rarity of childhood cancer. While differences in cancer registration practice must be taken into consideration when assessing cancer incidence rates across geographic populations, it is likely that there is true disparity in risk for many childhood cancers.
Increases in childhood cancer incidence since the 1960s and 1970s have been reported in Europe and the rest of the world.9-11 In Great Britain, the World age-standardised incidence rate has increased by more than two-fifths (43%) since the late 1960s, from 107 cases per million children in 1966-1970 to 152 cases per million children in 2001-2005.5 Between 1966 and 2000 there has been a statistically significant average increase of less than 1% per year, though this varies between 0.5% and 2.5% per year by tumour type (Figure 1.9).5
Results from the ACCIS project (A collaborative project of the European cancer registries. The ACCIS database contains over 160,000 records of childhood and adolescent cancer cases diagnosed from the late 1960s onwards) have shown slightly higher increases for Europe as a whole.9,12 Over a twenty year time period, the World age-standardised incidence rate for Europe significantly increased by an average of 1.1% per year, from 120 per million children in 1978-1982 to 141 per million in 1993-1997.9
This varied across Europe, ranging from an average annual increase of 1.0% per year in Northern Europe to 1.4% per year in Eastern Europe. Slightly lower average annual increases of 0.6% per year were observed in the US over a similar time period,24 and a more recent US study reported a slowing down of this increase to a non-significant average annual increase of just 0.4% per year since the early 1990s. Recent findings from an Australian study are also consistent with a plateau in childhood cancer incidence rates from the mid-1990s onwards.11 While some of the worldwide increases are likely to be due to real changes in risk, improvements in the efficiency of systems for the diagnosis and registration of childhood cancers since the 1960s and 1970s will also have played a part. 5,13,14
For many years it was widely believed that children of high socioeconomic status (SES), such as those living in relatively affluent areas, were at an increased risk of developing leukaemia (and ALL in particular). 18 The evidence is far from conclusive, however, and many more recent studies have published associations in the opposite direction, that is lower rates of leukaemia in children of high SES.19 A recent report from the UK Childhood Cancer Study concluded that SES is not a determinant of childhood ALL in the UK.20 One reason for the controversy is that different measures of SES represent different risk factors, making it difficult to compare studies over place and time. Population mixing might explain at least some of the observed association of ALL with affluence, since affluent populations tend to be more mobile and rural.21 This theory is also consistent with the hypothesis that some childhood leukaemias are the result of a rare response to an unidentified infection following geographic or social isolation early in life (see the Risk factors section).21-23
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