Childhood cancer: overview of incidence trends and environmental carcinogens
An estimated 8000 children 0 to 14 years of age are diagnosed annually with cancer in the United States. Leukemia and brain tumors are the most common childhood malignancies, accounting for 30 and 20% of newly diagnosed cases, respectively.
From 1975 to 1978 to 1987 to 1990, cancer among white children increased slightly from 12.8 to 14.1/100,000. Increases are suggested for leukemia, gliomas, and, to a much lesser extent, Wilms’ tumor.
There are a few well-established environmental causes of childhood cancer such as radiation, chemotherapeutic agents, and diethylstilbestrol.
Childhood cancer: overview of incidence trends and environmental carcinogens, Environ Health Perspectives, NCBI PubMed PMID: 8549470, 1995 Sep.
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Many other agents such as electromagnetic fields, pesticides, and some parental occupational exposures are suspected of playing roles, but the evidence is not conclusive at this time.
Some childhood exposures such as secondhand cigarette smoke may contribute to cancers that develop many years after childhood.
For some exposures such as radiation and pesticides data suggest that children may be more susceptible to the carcinogenic effects than similarly exposed adults.
Diethylstilbestrol exposure and Medications
Transplacental carcinogenesis was established by the discovery in 1971 of vaginal adenocarcinoma in the daughters of women who took the hormone diethylstilbestrol (DES) during pregnancy to avoid miscarriages. This very rare cancer has been detected in girls as young as 7 years old, with most affected between 15 and 22 years of age. There are concerns that at older ages the exposed daughters may also have increased risk of squamous carcinomas of the vagina and cervix and cancers of the breast and that exposed sons may have excess testicular and prostate cancer . Continued followup of the DES-exposed daughters and sons is ongoing at the National Cancer Institute and may provide further information on the late effects of DES and on transplacental carcinogenesis in general.
Suspected, but less well-established, of being a transplacental carcinogen is phenytoin, an antiepileptic drug. There are reports of neuroblastoma and soft tissue sarcoma in children exposed in utero to phenytoin.
There have also been reports of excess brain tumors, neuroblastomas, leukemia, and retinoblastomas in children of women who used antinausea medications (e.g., Bendectin) during pregnancy. This issue had received considerable publicity, however, which may have affected recall of use by study subjects. One study used medical records, not subject recall, to assess exposure and did not show any associations.
There is one report of excess Wilms’ tumor among Swedish children whose mothers were exposed to penthrane (methoxyflurane) anesthesia during delivery. The excess risk was higher in females and increased with age at diagnosis.
Some medical treatments received during childhood also play a role in the development of childhood cancer. Chemotherapy and radiation therapy received for an initial childhood cancer can dramatically increase the risk for second cancers. For example, in one study children treated with alkylating agents for cancer have a 5-fold risk of subsequently developing leukemia. At high doses, the risk was increased as much as 25 times the expected rate of leukemia. Bone sarcomas were also elevated in children treated with radiation and chemotherapy.
The potent antibiotic chloramphenicol, given to treat life-threatening infectious conditions, has been linked to excess acute lymphocytic leukemia and acute nonlymphocytic leukemia in children in Shanghai. This association with leukemia is consistent with a report of bone marrow depression following use of chloramphenicol.
Parental use of illegal drugs has been linked to childhood cancer in a few reports. Marijuana use was associated with rhabdomyosarcoma, leukemia, and brain tumors. Cocaine use was also associated with rhabdomyosarcoma.
These exposures are difficult to study accurately and need further research, but prevention efforts clearly must continue for noncancer-related reasons even in the absence of convincing data on childhood cancer.
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