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| 17.1 Cancer as a Genetic DisorderCancer in Families 1. The search for cancer genes in families has given way to a genomic approach to identifying cancer genes. 2. Carcinogens, most of which are mutagens, are cancer producing agents. 3. More than 100 oncogenes and 30 tumor suppressor genes have been identified. 4. DNA microarrays can be used to identify and distinguish different types of tumors. A Loss of Cell Cycle Control 1. Cancer is caused by a loss of cell division control. 2. Genes involved in the onset and progression of cancer include those encoding growth factors, transcription factors, DNA repair genes, and telomerase. Inherited versus Sporadic Cancer 1. Several mutations may contribute to the development of cancer. 2. Most cancers are sporadic and therefore, the causative mutation occurs in cells of the affected tissue. 3. Cancer may develop when an environmental trigger causes mutations in a somatic cell or when a somatic mutation compounds an inherited susceptibility. 17.2 Characteristics of Cancer Cells 1. Cancer cells do not respond to normal cell cycle control signals and as a result they grow vigorously and continuously. 2. The cancer phenotype is heritable and transmitted to daughter cells. 3. A cancer cell differs from normal cells in that it is transplantable (can be removed grow in a healthy animal), dedifferentiated (less specialized), lacks contact inhibition (will pile up on one another), and has surface structures that allow it to invade healthy tissue and metastasize (spread). 17.3 Genes that Cause CancerOncogenes 1. Many genes that normally control the cell cycle are proto-oncogenes. 2. Proto-oncogenes are transformed into oncogenes by mutations that increase the expression or alter the biological activity of their protein product. Tumor Suppressors 1. Mutations in tumor-suppressor genes that cause cancer are deletions causing loss of gene function. 2. Loss of tumor-suppressor genes enables cells to ignore extracellular constraints on cell division. 3. The RB, p53, and BRCA1 genes encode tumor suppressors. 17.4 A Series of Genetic Changes Causes Some CancersA Rapidly Growing Brain Tumor 1. Astrocytoma and FAP are two cancers that require several mutations to develop. 2. A series of genetic alterations recorded for astrocytoma involve loss of function for both p53 alleles, loss of interferon and tumor suppressor genes on chromosome 9, activation of an oncogene on chromosome 7, and loss of chromosome 10. Colon Cancer 1. FAP begins in early childhood with precancerous growths called polyps. 2. An autosomal dominant pattern of inheritance is associated with FAP and it occurs with a frequency of one in 5000 people in the United States. 3. A dominant mutation in the APC gene on chromosome 5 is the first step in the multi-step model for colon cancer. 4. Subsequent mutations in chromosomes 12p (Ras), 18q (DCC) and 17p (p53) cause the transformation of the polyp into a tumor. 17.5 Cancer Prevention and TreatmentDiet-Cancer Associations 1. Epidemiological studies are used to identify risk factors in a population. 2. Avoiding fats along with with eating more fruits, vegetables, and whole grain cereals is associated with a lower cancer risk. Diagnosing and Treating Cancer 1. Testing can identify family members at risk of inherited cancers. 2. Treatments for cancer target the characteristics of cancer cells. 3. Surgery removes tumors. 4. Chemotherapy and radiation nonselectively destroy rapidly dividing cells. 5. Newer treatments target receptors on cancer cells, block telomerase, trigger redifferentiation, or attack a tumor's blood supply. |