Rates and Risk Factors
Rates and Risk Factors
Lymphomas affect the white blood cells of the immune system and are characterized by abnormal growth of lymphocytes, the infection-fighting cells in the lymph nodes, spleen, and thymus.6 Lymphomas are the third most common cancer among children. Hodgkin's lymphoma accounts for about half of these lymphomas. Others are often combined under the label "non-Hodgkin's lymphoma" (NHL), and several types of NHL, such as Burkitt's lymphoma, are often listed separately.
The incidence of lymphomas was 1.8 per 100,000 among children living in NJ during 1979-1995 and 1.6 per 100,000 among children living in the US during 1979-1994 (Table 1a). Among NJ boys, the incidence of lymphoma was 2.4 per 100,000, while the corresponding rate among US boys was 2.0 per 100,000. For unknown reasons, this difference is accounted for by different rates among black children. In NJ, black children have the same rates as white children, but for the US as a whole, black children have lower rates than white children (Table 1b). The incidence rate among NJ girls is the same as that for US girls (1.1 per 100,000). Among NJ children, the incidence of Hodgkin's lymphoma was 0.7 per 100,000 and the incidence of non-Hodgkin's lymphoma was 0.6 per 100,000. Burkitt's lymphoma was the third most common lymphoma in NJ with an incidence of 0.3 per 100,000 children.
Incidence and Mortality Trends
Figure 6 shows the incidence and mortality trends for childhood lymphoma. The incidence rates for NJ were constant at just under 2.0 per 100,000 children. The national incidence rates were constant and slightly less than those in NJ. Mortality rates were extremely low for NJ and the US. The NJ mortality rate declined from 0.3 to 0.2 per 100,000 over the period, while the US mortality rate was constant at about 0.2 per 100,000 children.
Figure 7 shows the trends in incidence and mortality rates for Hodgkin's lymphoma. Hodgkin's lymphoma incidence rates in NJ and the US were constant at just under 1.0 per 100,000 children throughout the period. Mortality rates in NJ and the US were very low between 1979-81 and 1983-85 and were negligible after 1983-85.
Figure 8 shows the incidence and mortality rates for non-Hodgkin's lymphoma in NJ and the US. NJ incidence of non-Hodgkin's lymphoma increased slightly from 0.5 per 100,000 to 0.7 per 100,000 children, while US incidence increased from 0.5 per 100,00 to 0.6 per 100,000 children. Mortality rates for non-Hodgkin's lymphomas were very low and constant at approximately 0.1 per 100,000 children.
Demographic Patterns, Types of Lymphomas and Survival Rates
The incidence of Hodgkin's lymphoma increases with age and peaks at ages 25 to 29. Overall, male rates are higher than female rates in childhood, and white children have a higher incidence rate than black children. Five-year survival rates for Hodgkin's lymphoma have improved from 79 percent in 1974-1976 to approximately 92 percent in 1989-1994.2
The incidence of non-Hodgkin's lymphoma (NHL) increases sharply in the first five years of life and continues to increase at a slower rate thereafter. The incidence rates are higher for boys than girls and are also higher for black children than for white children. The five-year survival rate for NHL among children has increased from 45 percent in the 1974-76 period to 78 percent in the 1989-1994 period.
Burkitt's Lymphoma Burkitt's lymphoma is a type of non-Hodgkin's lymphoma. In Africa, Burkitt's lymphoma has been linked to malaria and Epstein-Barr virus, however in the United States, both malaria and Epstein-Barr are uncommon suggesting different origins from the disease in Africa. The incidence of Burkitt's lymphoma is higher in white children than black children in the United States.
Immunodeficiency is associated with lymphoma. Non-Hodgkin's lymphoma in children is believed to be related to several rare, genetically determined, immune system diseases. Hemophilia patients who have been exposed to human immunodeficiency virus (HIV) have an increased risk of experiencing NHL, and transplant patients (who are deliberately immunosuppressed) have a substantially increased risk of developing lymphomas.6, 7, 17
NERVOUS SYSTEM CANCERS
Cancers of the Brain and Spinal Cord (Central Nervous System)
The central nervous system (CNS) is made up of the brain and spinal cord. Cancers of the central nervous system are the second most common type of childhood cancer after the leukemias. These cancers occur primarily in the brain. The most common form of CNS cancers are glioma, followed by primitive neuroectodermal cancers (PNET) which account for nearly a quarter of central nervous system cancers in children. Gliomas comprise several different types of cancers, including astrocytomas.
The incidence rate of cancers of the central nervous system during 1979-1995 among children in NJ, as well as among children in the US, was 2.9 per 100,000 children (Table 1a). Among NJ boys, the incidence rate was 3.2 per 100,000 and among NJ girls the incidence rate was 2.7 per 100,000. The corresponding rates for the US were similar. Among white children in NJ, the incidence of CNS cancers was 3.0 per 100,000 and among black children in NJ the incidence rate was 2.4 per 100,000 (Table 1b). The incidence of astrocytomas was about 1.4 per 100,000 among children in the US and NJ, accounting for almost half of all CNS cancer. Primitive neuroectodermal cancers had an incidence of 0.6 per 100,000 and were the second most common cancer of the central nervous system.
Incidence and Mortality Trends
Figure 9 shows the incidence and mortality rates for cancers of the central nervous system. The New Jersey CNS incidence rate peaked in the years 1983 and 1984 at 3.6 per 100,000 and then declined sharply to 3.0 per 100,000 in 1985. After 1985, the NJ CNS cancer incidence rate increased gradually to about 3.2 per 100,000 in 1994. CNS cancer incidence rates for the US have increased steadily over time from approximately 2.4 per 100,000 in 1980 to about 3.2 per 100,000 in 1993. NJ incidence rates were previously higher than the national rates, but the gap has narrowed over time.
The NJ mortality rate peaked at 1.4 per 100,000 in 1983 and declined to 0.8 per 100,000 in 1986. Since 1986, the morality rate has remained essentially unchanged. For the US, mortality rates have been approximately constant at about 1.0 per 100,000.
The age-specific patterns for glioma and PNET are similar. The incidence of these cancers peak at or just below age five and then decline. Boys and girls have the same incidence of glioma, while boys have higher rates of PNET. White children have higher incidence of CNS cancers than black children.
There has been much progress in the treatment of children with brain cancers. Note that the mortality rates for NJ and the US have been steady since 1986 (Figure 9). The five-year survival rate for all brain cancers combined is about 60 percent, and children with astrocytoma have a five-year survival rate of about 70 percent.6, 18
Some genetic disorders, such as neurofibromatosis and the Li-Fraumeni family cancer syndrome, have been linked to increased incidence of CNS cancers.6
High doses of ionizing radiation have been linked to cancers of the nervous system, however less is known about low levels of radiation exposure and the risk of CNS cancers.6
Several studies have reported significant associations between parental occupation and risk of brain cancers.18-20 The exposures studied included ionizing radiation, pesticides, chemical solvents, and polycyclic aromatic hydrocarbons. The industries examined included airline, electronic, chemical and drug sales, printing, and agricultural.
Other Parental Exposures
A class of chemicals called N-nitroso compounds were found by some researchers, but not by others, to be related to brain cancers in children of parents exposed through various means. Nitroso compounds are found in cured meats, burning incense, second-hand cigarette smoke, some facial cosmetics and antihistamines. By contrast, several studies on the use of vitamin supplements and high consumption of fruits and vegetables during pregnancy have shown a protective effect against brain cancer development in children, especially for children under age five.6, 22, 23
Various epidemiological studies since the late 1970s found weak associations between extremely low-frequency electromagnetic fields, e.g. power lines, and brain cancers. However, these studies were limited by difficulties in measuring exposure. More recent studies which have better measures of exposure have not confirmed the findings of the earlier reports.
Sympathetic Nervous System Cancers
The sympathetic nervous system (SNS) is the part of the nervous system that controls the vital functions of the body that are not consciously regulated. It includes the activity of the heart, the smooth muscles (such as digestive muscles), and glands. Cancers of the sympathetic nervous system include neuroblastoma and ganglioneuroblastoma. Neuroblastoma is the most common childhood cancer of the SNS. It is a cancer of the peripheral nervous system and can occur almost anywhere in the body.
Cancers of the sympathetic nervous system occurred at a rate of 1.0 per 100,000 among NJ and US children during 1979-1995 (Table 1a). While the incidence among US boys was equal to that of US girls, incidence was slightly higher among NJ boys (1.1 per 100,000) than among NJ girls (0.9 per 100,000). The incidence of SNS cancers among white children in NJ (1.0 per 100,000) was slightly higher than among black children in NJ (0.8 per 100,000). Neuroblastoma accounted for nearly all of the SNS cancers.
Demographic Patterns, Risk Factors and Survival Rates
Neuroblastomas arise during pregnancy. This cancer is typically diagnosed in infancy. It is the most common neoplasm in children under one year of age. Incidence rates of neuroblastoma are highest among white children and are higher among boys than girls. About one percent of neuroblastomas are attributed to known genetic diseases. There has been very little research on the effects of environmental exposures and the risk of neuroblastomas. The five-year survival rate for neuroblstoma is about 65 percent, and for ganglioneuroblastoma is approximately 85 percent.6, 7, 18