Understand Childhood Cancers and Blood Disorders
Causes of Cancer
While much has been learned about the biology of cancer in recent years, no single clear-cut cause has been established. Cancers are a very diverse group of diseases with different symptoms and behaviors. As such, it is no surprise that these illnesses arise because of different factors. And while a straightforward cause and effect does not exist for most childhood cancers, many risk factors have been identified that predispose people to developing cancer.
Genetics and inheritance factors play an important role in some cancers. Some cancers, including retinoblastoma, an eye tumor, Wilms tumor, a cancer of the kidney, and Hodgkin’s lymphoma have been seen in parents and their children. An identical twin whose sibling is diagnosed with acute lymphoblastic leukemia has a very strong likelihood of developing the same illness, particularly if the children are young. Children with chromosome disorders, such as Downs Syndrome and Fanconi’s Anemia are at high risk for developing leukemia. Other inherited syndromes, such as neurofibromatosis, Bloom’s Syndrome, osteogenesis imperfecta, and tuberous sclerosis, have a strong association with brain tumors.
Infections have been associated with many different cancers. Epstein Barr Virus, the cause of infectious mononucleosis, has a strong association with Burkitt’s Lymphoma in African children, nasopharyngeal carcinoma in the Far East, and Hodgkin’s Lymphoma in the United States. Chronic hepatitis can lead to hepatocarcinoma, a cancer of the liver. Human immunodeficiency virus has been associated with a variety of cancers, including lymphoma, Kaposi sarcoma, and leiomyosarcoma. Human papilloma virus can lead to cancer of the cervix years later. T-cell leukemia is sometimes associated with another virus, HTLV.
Immunodeficiency disorders, whether inherited or acquired, are often associated with a variety of cancers, particularly B-cell leukemia and lymphoma. Agammaglobulinemia, severe combined immunodeficiency, and Wiskott Aldrich Syndrome are some of the inherited conditions that predispose to cancer. Medications such as azathioprine and cyclosporine, used to suppress the immune system for transplants and other conditions, are risk factors for lymphomas.
Radiation exposure has been established for many years to be a risk factor for cancer development. Children exposed to radiation from nuclear fallout have a high incidence of leukemia and thyroid cancer. Therapeutic radiation for conditions such as ankylosing spondylitis, enlarged tonsils, and tinea capitis have all been linked with cancer. Exposure to high doses of medications such as alkylating agents (such as nitrogen mustard and cyclophosphamide used to treat cancers), topoisomerase inhibitors (such as etoposide, also used for cancer therapy), and the anticonvulsant diphenylhydantoin have all been implicated to some extent with the development of cancer.
An area of intense research has been the investigation of changes in genetic material when cells become cancerous. Most patients with leukemia are found to have marker chromosomes that indicate a molecular change in the white cell; these altered chromosomes determine the behavior of the cells and serve as markers to follow the status of the disease. Oncogenes such as N-myc in children with neuroblastoma have been found to give important prognostic information altering how a patient is subsequently treated.
It is quite clear from all of the above that there is no one cause of cancer. While there are fundamental changes that occur in the genetic material of the cancerous cell, there are numerous agents and triggers that play an important role in making these changes. The challenge to medical science is to further the understanding of the process and find ways to reverse it.