Definition:
cancer (malignant tumor) is defined as the abnormal, excessive, uncoordinated, autonomous and purposeless proliferation of cells (in any tissue or organ of the body), which have the tendency to spread & grow in other parts of the body.
Causes & Prevention of Cancer :
Most of the human cancers are caused by certain:
1. chemical.
2.physical
3.biological agents.
1. chemical.
2.physical
3.biological agents.
The process by which normal cell convert to cancer cell is called malignant transformation.
collectively known as carcinogens.
Role of Heredity:
Familial retinoblastoma, familial adenomatous polyposis, multiple endocrine neoplasia syndrome and hereditary breast & ovarian cancer syndromes.
Members of these families have one or more activated oncogenes in their inherited genome. Therefore fewer additional mutations are required in these persons for the cancer to development.
In most cancers genetic mutations are not inherited and arise in a somatic cells during adulthood as a result of exposure to environmental carcinogens.
In mutations (inherited and acquired) commonly involved three types:
1.Tumor suppressor genes
2.Oncogenes
3.genes involved in DNA repair mechanism.
Members of these families have one or more activated oncogenes in their inherited genome. Therefore fewer additional mutations are required in these persons for the cancer to development.
In most cancers genetic mutations are not inherited and arise in a somatic cells during adulthood as a result of exposure to environmental carcinogens.
In mutations (inherited and acquired) commonly involved three types:
1.Tumor suppressor genes
2.Oncogenes
3.genes involved in DNA repair mechanism.
Tumor suppressor genes:
Retinoblastoma 13 (13q14)
Rb is a tumor suppressor gene. Common in children. Both eyes can be affected. Inherited as an autosomal dominant trait. The gene is located in the proximal long arm of chromosome 13(13q14), where the functional protein of this gene is not absent.
p53
p53
Mutation of the tumor suppressor gene p53 which is located in 17q causes cancer of:
1.Colon cancer
2.Lung cancer
3.Breast cancer
4.Brain cancer
5.Hepatocellular carcinoma
6.Chronic myeloid leukemia in blast crisis.
The most important tumour suppressor genes known so far is:
p53 gene that suppresses uncontrolled proliferation of cells as well as triggers apoptosis (Mutations in p53 gene are seen in about 50 per cent cases of human cancers.
Rb gene (associated with Retinoblastoma and osteo-sarcoma).
Ret gene (associated with Endocrine cancer);
WT-1 (associated with Wilm's tumour);
NF-1 (associated with Neurofibromatosis type-1);
NF-2 (associated with Neurofibromatosis type-2);
APC and DCC (associated with the colon cancer).
Oncogenes:
Cellular oncogenes (c-onc) can be activated to cause cancer as a result of chromosomal rearrangement, e.g. in CML where Ph chromosome can be seen in the malignant bone marrow cells. As a result of this reciprocal translocation of the ABL gene to BCR gene, as a result a novel protein is produced which is said to be the cause of malignancy.
Genes involved in DNA repair mechanisms:
DNA repair mechanisms exist to correct DNA damage due to environmental; mutagens and accidental base misincorporation at the time of DNA replication. Inherited defects in either system can lead to cancer. Example is xerodermal pigmentosum which is an autosomal recessive disorder in DNA repair mechanism after exposure to ultraviolet light.
