The Genetics of Cancer
Jan 01, 2016
The Genetics of Cancer
Human and Cancer
Life and adaptation
cell division
Cancer in the media
cancer is a disease of the cell cycle
Synth. Of RNA & proteins
Cont. Of RNA
Chromosomes are attached to the spindle
G1 checkpoint
G1
S
M
M checkpoint
G2 checkpoint
G2
Controlsystem
DNA damage or broken
In complete DNA replication
G1
G1 checkpoint
G1
G0
If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.
If a cell does not receive a go-ahead signal at the G1 checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.
Unlimited number of cell divisions.Growth without external signals.Failure to respond to 'stop' signalsAvoidance of cell death.The ability to leave the original tumor location and form a new tumor, or metastasis.
Cancer terminology
Classification by tissue type:• carcinoma
epithelial cell90% of all tumoursderived from ectoderm (mostly) or endoderm (some)
• sarcomaconnective tissue2% of all tumoursderived from mesoderm
• leukaemiacirculatory or lymphatic8% of all tumoursderived from mesoderm
• Myeloidblood cell
• Lymphoidlymphocytes or macrophages
• Central nervous system cancers of the brain
Main Features of Benign and Malignant Tumors
Cancer Spreads Step-by-Step
A Common Type of Colorectal Cancer May Develop by These Steps
Types of genes which may mutate to cause cancer:
• Tumor suppressor genes– Stop cell growth and division; prevent cancer
formation– May prevent expression of oncogenes– Retinoblastoma: only one functional copy of a
tumor suppressor gene on chromosome 13– BRCA1 and BRCA2– p53: codes for a regulatory protein that turns off
cell division when the cell is stressed or damaged
Types of cancer genes
Types of proteinsTypes of proteinsMutated functionMutated functionNormal functionNormal functionType of geneType of gene
Enzymes for mismatch or excision repair
Fail to repair DNA mutations
Repair DNA mutations
DNA repair gene mutation
Checkpoint molecules
Fails to suppress division
Suppresses cell division
Tumor suppressor gene
Growth factorsPromotes division - abnormal time or cell type
Promotes divisionOncogene
Tumour suppressor genes
• The gene’s normal function is to regulate cell division. Both alleles need to be mutated or removed in order to lose the gene activity.
• The first mutation may be inherited or somatic.• The second mutation will often be a gross event
leading to loss of heterozygosity in the surrounding area.
Oncogenes
• Cellular oncogene c-onc• Viral oncogene v-onc• Proto-oncogene, activated by mutation
to c-onc
Proto-oncogene activation
Other Factors Also May Lead to Cancer
• Inherited susceptibility to cancer– ~5% of cancers
• Viruses– Viral DNA may be inserted into a host cell’s DNA • May switch on a proto-oncogene• May carry oncogenes
Other Factors Also May Lead to Cancer
• Chemical carcinogens– Carcinogens: cancer-causing substances that can
lead to a mutation in DNA• Hydrocarbons in cigarette smoke• Aflatoxin: fungal product
• Radiation– UV from the sun and tanning lamps– X-rays: medical and dental– Radon, cosmic rays, and gamma radiation
Some Industrial Chemicals Linked to Cancer
In the U.S., More than 1 Million People Are Diagnosed with Cancer Each Year
Biopsy Is the Only Sure Way to Diagnose Cancer
• Biopsy– Removal and microscopic examination of tissue
Light Microscope Image Shows Cancerous Cells in Breast Tissue
Cancer Treatment and Prevention
• When a person is diagnosed with cancer, a variety of weapons are available to combat it
Chemotherapy drugs
Radiation therapy
Surgery
Chemotherapy and Radiation Kill Cancer Cells
• Chemotherapy– Drugs used to kill cancer cells; disrupt some aspect
of cell division– Toxic to healthy cells; hair, bone marrow,
lymphocytes, and epithelial cells of intestinal lining – Side effects include hair loss, nausea, vomiting, and
reduced immune responses– Genetic approach to chemo in the future
Chemotherapy and Radiation Kill Cancer Cells
• Radiation therapy– Used when cancer is small or has not
spread– Radioisotopes used, e.g., Ra-226 and
Co-60
• Chemotherapy and radiation destroy healthy cells
• More precise treatments– Monoclonal antibody treatment– Interferon treatment; limited at
present
Good Lifestyle Choices Can Limit Cancer Risk
• Avoid tobacco completely
• Maintain a desirable weight; eat a low-fat diet with plenty of fruits and vegetables
• Drink alcohol in moderation
• Make sure your living and work environment is safe from carcinogens
• Protect your skin from the sun’s UV rays
This Cancer Cell Is Surrounded by White Blood Cells
Cancer Causes and Contributing Factors
What mark have you thought to leave after?What mark have you thought to leave after?29