Cancer is not caused by a single factor. Instead, it arises from a complex interplay of various elements. Scientists believe that cancer development is usually due to a combination of genetic predispositions, environmental influences, and individual characteristics.
It’s important to understand that cancer in children differs significantly from cancer in adults, particularly in terms of diagnosis, treatment approaches, and prognosis. A key difference lies in the survival rates and the underlying causes of the disease. Childhood cancers have a notably higher overall five-year survival rate, around 80%, compared to adult cancers, which stand at approximately 68%. This disparity is largely attributed to the fact that childhood cancers often respond more favorably to treatment, and children can generally tolerate more intensive therapies.
The origin of childhood cancers often traces back to stem cells. These are basic, unspecialized cells that have the capacity to develop into various specialized cells required by the body. Childhood cancer is frequently triggered by a sporadic cell change or mutation that occurs randomly. In contrast, adult cancers typically originate in epithelial cells. These cells form the lining of body cavities and the outer layer of the skin. Cancer in adults often develops due to accumulated environmental exposures affecting these epithelial cells over time. For this reason, adult cancers are sometimes referred to as “acquired” cancers.
Understanding Cancer Risk Factors
As previously mentioned, certain cancers, especially those occurring in adults, have been linked to repeated exposures or specific risk factors. A risk factor is defined as anything that increases an individual’s likelihood of developing a particular disease. It’s crucial to note that a risk factor doesn’t directly cause the disease, but it can weaken the body’s defenses against it. Several risk factors and mechanisms have been identified as potential contributors to cancer:
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Lifestyle Choices: Certain lifestyle factors significantly elevate the risk of some adult cancers. Smoking, diets high in fat, and occupational exposure to toxic chemicals are prime examples. However, most children diagnosed with cancer are too young to have experienced prolonged exposure to these lifestyle-related risk factors.
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Family History, Heredity, and Genetic Predisposition: Genetics can play a substantial role in the development of some childhood cancers. It’s not uncommon to find instances of various forms of cancer occurring within the same family. In such cases, it’s often challenging to pinpoint the exact cause. It could be due to an inherited genetic mutation, exposure to environmental toxins in the family’s living environment, a combination of both, or simply a matter of coincidence.
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Genetic Disorders: Certain genetic disorders are known to compromise the immune system, thereby increasing cancer risk. Conditions like Wiskott-Aldrich syndrome and Beckwith-Wiedemann syndrome are examples. The immune system is a complex network that protects the body from infections and diseases. Bone marrow is responsible for producing cells that mature and become key components of the immune system. One theory suggests that damage or defects in bone marrow stem cells can lead to the production of abnormal or cancerous cells when these stem cells reproduce. The underlying cause of these stem cell defects could be inherited genetic flaws or exposure to viruses or toxins.
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Viral Exposures: Exposure to certain viruses has been linked to an increased risk of developing specific types of childhood cancers. Epstein-Barr virus and HIV, the virus that causes AIDS, are associated with a higher incidence of cancers like Hodgkin lymphoma and non-Hodgkin lymphoma. It’s believed that these viruses can alter cells, causing them to reproduce in an altered state. Over time, these alterations can progress into cancerous cells that continue to multiply and spread.
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Environmental Exposures: The potential link between environmental exposures and childhood cancers has been a subject of research. Pesticides, fertilizers, and power lines have all been investigated for a direct connection. There have been instances of cancer clusters among unrelated children living in the same neighborhoods or cities. However, whether prenatal or early infant exposure to these agents directly causes cancer, or if these occurrences are coincidental, remains unclear.
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High-Dose Chemotherapy and Radiation: Paradoxically, certain cancer treatments can themselves increase the risk of developing secondary cancers later in life. Children who have undergone high-dose chemotherapy and radiation are at risk of developing a second malignancy. These powerful anticancer treatments can sometimes alter cells and/or weaken the immune system. A second malignancy is a new cancer that arises as a consequence of treatment for a previous, different cancer.
The Role of Cancer Genes
How Genes Influence Cancer Development
A significant breakthrough in cancer research has been the identification of specific genes that play a role in cancer development. It’s estimated that over 90% of cancers exhibit some form of genetic alteration. These genetic changes can be inherited, meaning they are passed down from parents, or they can be sporadic, arising randomly or as a result of environmental exposures, often over many years.
Types of Genes Involved in Cancer
There are three primary categories of genes that can impact cell growth and are frequently found to be altered (mutated) in various types of cancers:
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Oncogenes: These genes are responsible for regulating normal cell growth and division. Scientists often describe oncogenes as being like a cancer “switch” that exists in everyone’s body. However, what triggers these oncogenes to lose their ability to control normal cell growth, leading to the uncontrolled proliferation of abnormal cancer cells, is still largely unknown.
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Tumor Suppressor Genes: These genes act as guardians against cancer. They have the ability to detect abnormal growth and replication of damaged cells or cancer cells. When they identify such abnormalities, they can halt cell reproduction until the defect is corrected. However, if tumor suppressor genes become mutated and malfunction, they lose their ability to control cell growth, and tumor development can occur.
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Mismatch-Repair Genes: These genes play a crucial role in maintaining the integrity of DNA during cell division. When DNA is copied to create new cells, mismatch-repair genes identify and correct errors that may occur during this process. If the DNA copies don’t “match” perfectly, these genes repair the mismatches and rectify the errors. However, if mismatch-repair genes are not functioning correctly, errors in DNA can be passed on to new cells, causing damage and potentially leading to cancer.
