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Cellular Basis of Cancer. Dr Rosemary Bass [email protected]. Cancer: Characteristics of cancer cells Malignant & benign tumours O ncogenes & tumour suppressor genes (TSG) Invasion, Metastases , Angiogenesis . . Contents. Introduction. Causes. History. Terminology. - PowerPoint PPT Presentation
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Cellular Basis of Cancer
Dr Rosemary [email protected]
Cancer:
Characteristics of cancer cells
Malignant & benign tumours
Oncogenes & tumour suppressor genes (TSG)
Invasion, Metastases, Angiogenesis.
•Causes
Contents• Introduction
•History
•Terminology• Incidence Rates
•Cancer Types
•Progressive Nature of Cancer
• "cancer" from latin for "crab"
•disease of higher, multicellular organisms
•cell growth is dysregulated (abnormally controlled)
Introduction to Cancer
Cancer is a disease where cells grow out of control and invade, erode and destroy normal tissue. The driving forces behind the development of cancer are damaged genes.
Cancer develops when cells start to divide at the wrong time and in the wrong place, then continue to divide and invade nearby tissues and organs. It is this uncontrolled growth of cells that causes a swelling or tumour.
Cancer is not one disease but many, all with some similar features but all with a distinctive character, which varies according to the cancer's type and location.
www.cancerresearchuk.org
www.mariecurie.org.uk
www.macmillan.org.uk
What is cancer?
• Is cancer a modern disease?(David & Zimmerman (2010) Nat Rev Can10,728).
•Cancer occurs in all higher animals
•Evidence from ancient pictures & writings
Cancer - Background
• Increased incidence of cancer due to humans living longer - fewer deaths from infectious diseases
•Bone cancers found in Egyptian mummies•But rare in comparison to modern incidence
info.cancerresearchuk.org
•Pott suggested soot as causative agent - carcinogen
Cancer - History•Percival Pott (1775) - first scientific investigation of cancer
iaphomepage.org/ int302/potts
•Scrotal cancer in men who had been boy-sweeps
iaphomepage.org/ int302/potts
•Advised frequent washing and changes of clothes
•First epidemiological study on cancer
•Terms "cancer", "neoplasm" and "tumour" often used interchangeably
•Cancer usually means carcinoma (malignant tumour of epithelial origin)
Introduction to Cancer
•Neoplasm usually means the newly-formed tumour
•Tumour refers to any benign or malignant growth
•Cancer is "new growth resulting from abnormal proliferation of transformed cells"
•Growth may be rapid, moderate or slow vs normal cells
•Cancer is now the second most common cause of death in developed countries (after cardiovascular disease)
•The clinical study of cancer is "oncology"
Introduction to Cancer (2)
One in three people will be diagnosed with cancer
One in four people will die from cancer
Every two minutes someone is diagnosed with cancer in the UK (<300,000 new cases p.a.)
Cancer affects mainly older people.
Deaths from cancers of the lung, bowel, breast and prostate together account for 54% of all cancer deaths.
Cancer Incidence
http://info.cancerresearchuk.org/cancerstats/keyfacts/?a=5441http://info.cancerresearchuk.org/cancerstats/incidence/
• Cancer is a large collection of many diseases, with many causes
• Cancer kills because the uncontrolled replication of cells within the tumour disrupts the structural integrity of the patient – leading to the spread of the disease – metastasis
• With demographic shifts in the population, such that the population in Western countries is increasingly aged, this will lead to increased prevalence of cancer.
Report from Foresight Ageing Population Panel ,The Age shift - priorities for action, http://www.education.edean.org/pdf/Intro013.pdf
• Cancer rare in young, increased incidence with age
- lung
Cancer More Common in Some Tissues•most common types in men:
- prostate- colon rectum
•most common types in women:
- breast- cervix- colon rectum - lung
The 20 Most Commonly Diagnosed Cancers, UK 2008(Excluding Non-Melanoma Skin Cancer)
Non-melanoma skin cancer (NMSC) = very common condition, BUT it is curable in the vast majority of cases.
NMSC routinely omitted from the overall total for new cases of cancer
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10 Most Commonly Diagnosed Cancers in Males, UK 2008(Excluding Non-Melanoma Skin Cancer)
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10 Most Commonly Diagnosed Cancers in Females, UK 2008(Excluding Non-Melanoma Skin Cancer)
Cancer survival figures are usually written as a % or number of patients alive five years after diagnosis.
This does not necessarily mean that the patient is cured:No recurrence of cancerRecurrence of cancer but alive Recurrence after the five years.
The figures quoted are true for the population but not for an individual.
Cancer Survival
http://www.ncsdf.org/
Causes of cancer
• Hereditary (though probably <5%)
• Environmental: radiationchemicalhazards in workplace
• Lifestyle dietsmokingalcohol
sex
• Viruseshttp://info.cancerresearchuk.org/cancerstats/causes/lifestyle/tobacco/
• Most cancers are “avoidable” – being due to environmental and lifestyle factors
• 1/3 of ALL cancers are attributable to SMOKING
http://info.cancerresearchuk.org/cancerstats/causes/lifestyle/tobacco/
Cancer Research-UK data on risk of lung cancer in relation to intensity of smoking and age at which smoking ceased.
http://info.cancerresearchuk.org/cancerstats/causes/lifestyle/tobacco/
Diet is also a major factor in cancer incidence
• Data above show breast cancer incidence relation to dietary fat.• Similar relationships hold for prostate & other cancers. • The importance of diet & lifestyle in cancer incidence is shown
by “epidemiological” studies. • Early epidemiological studies of Japanese people who moved
to N. America showed that after 1 generation this population had the same breast cancer risk as the general N. American population.
Origins of Cancer• There are many connections between embryogenesis & cancer
• Most tumours arise in the cells that come in contact with the outside world & these are epithelial cells – i.e. the epidermal keratinocytes of the skin, epithelial cells lining digestive tract, respiratory system etc.
• Cancers are classified differently based on their cell of origin:
Epithelial cancers = carcinomasMesenchymal (ie connective tissue cell types such as fibroblasts) cancers = sarcomasBlood/lymphoid tissue = leukaemias/lymphomas
•suffix "-oma" defines solid tumour
Terminology (2) - Examples2. Solid Tumours
•prefix defines tissue type eg:
- adenoma = benign tumour of glandular tissue
- fibroma = benign tumour of connective tissue
- fibroadenoma = mixed tumour of glandular + connective tissue
- sarcoma = malignant tumour of connective tissue cells
Terminology (3) - Examples- carcinoma - malignant tumour of
epithelial cells
- adenocarcinoma = malignant tumour of glandular epithelium
others
- lymphoma = tumours of lymph tissue- teratoma = primitive germ cell tumour of gonads
Tissue Proliferation Rates
•Rapid Proliferation – bone marrow, gastrointestinal mucosa, ovary, testis, hair follicles
•Slow Proliferation – lung, liver, kidney, endocrine glands, vascular endothelium
•Almost no Proliferation – muscle, bone, cartilage, nerve
The molecular genetic basis of cancer
• Cancer is a genetic disease• Cancer arises from mutations in critical genes
Proto-oncogenes- the “accelerators” Tumour suppressor genes (TSGs) – the “brakes”
• Cancer is a multistep process involving a series of genetic 'hits‘
• Cancer is clonal - one cell 'goes wrong‘• Many factors working both inside and outside
the cell can determine a cell’s likelihood of sustaining genetic damage
Oncogenes
Causes of Cancer - Genetic Factors
• retroviral cancer-causing genes
• cellular equivalents = proto-oncogenes
•encode growth factors (GFs), GF receptors or nuclear proteins
First identified Oncogene:Rous isolated virus from spontaneous chicken sarcomas = Rous Sarcoma Virus (RSV) (retrovirus)
29
WHAT ARE ONCOGENES?
"A gene that causes the transformation of normal cells into cancerous tumour cells."
"Mutated and/or over-expressed version of normal gene, that in a dominant fashion releases the cell from normal growth restraints."
GAIN OF FUNCTION
A proto-oncogene is the wild-type allele (normal gene) of an oncogene.
Activating mutation of proto-oncogene creates the oncogene
One allele usually only affected = DOMINANT
WHAT SORTS OF GENES HAVE THE POTENTIAL TO BE ONCOGENES?
growth factors
growth factor receptors
G proteins
cytoplasmic tyrosine kinases
serine-threonine kinases
other cytoplasmic proteins
nuclear proteins
Oncogene FunctionGrowth Factors int-1 matrix proteinsis
Platelet derived growth factor
Growth-Factor Receptor (Tyrosine Kinase type) erb-B Epidermal growth factor receptorkit
Stem cell growth factor receptormet
Hepatic growth factor receptorros
Unknown ligand
G proteins H-ras
GTPase
K-ras
GTPase
N-ras GTPase
ret Glial-derived neurotrophic factor with GFR-a1-4 receptors
33
Cytoplasmic Tyrosine Kinasesbcr-abl Tyrosine kinasehck Tyrosine kinaselck Tyrosine kinase
src Tyrosine kinase
Serine-Threonine Kinases raf/mil Serine-Threonine Kinase
Other cytoplasmic proteins bcl-2 Prolongs life-span of cell
Nuclear proteins erb-A
Thyroid hormone receptorfos Transcription factorL-myc Transcription factormyc Transcription factor
Oncogene Function
HOW ARE PROTO-ONCOGENES ACTIVATED?
Mutation
Amplification
Translocation
Deletion or point mutation in coding sequence
DNA
RNA
hyperactive protein made in normal amounts
fusion to activelytranscribed genegreatly overproducesfusion protein; or fusionprotein is hyperactive
Chromosome rearrangement
nearby strong enhancer causes
normal protein to be overproduced
Gene Amplification
normal protein greatly overproduced
ACTIVATION OF PROTO-ONCOGENES
Tumour Suppressor Genes (TSGs)•100s recessive genes that normally regulate or suppress cell growth
• loss of function of TSG can lead to tumour formation or progression
•first identified in rare, inherited childhood tumours (retinoblastoma)
•TSG protein functions may be tissue-specific (RB - retina; BRCA1 - breast, ovary etc.)
HOW CAN TUMOUR SUPPRESSOR GENES BE LOST?
Mutation
Deletion
Loss of heterozygosity (allelic deletion)
Methylation
Haploinsufficiency
LOSS OF HETEROZYGOSITY (LOH)
Heterozygosity = individual is heterozygote for a genotype
1 normal gene, 1 mutated gene
When second copy is mutated (doesn't have to be the same mutation) neither allele will have functioning gene - homozygous for mutated gene, hence LOH
Evolving tumour cells can discard the second, still functional tumour suppressor gene copy
Also occur via missegregation or mitotic recombination
39
PROMOTER METHYLATION epigenetic
Methyl groups attached to cytosines at CpG
CpG methylation causes repression of transcription (if present in promoter of gene)
Histone deacetylases (HDACs) recognise and bind MeCpG• acetate groups removed from histones• resulting chromatin configuration
disfavours transcription
40
HAPLOINSUFFICIENCY
Heterozygous for a certain gene mutation or hemizygous (only one copy) at a particular locus (often due to a deletion of the corresponding allele) is clinically affected because a single copy of the normal gene is incapable of providing sufficient protein production as to assure normal function
Human Rb+/- develop normallyMouse Smad4+/- predisposed to tumours in stomachMouse p27Kip1+/- tumour proneMouse PTEN+/- acceleration of prostate cancer and Human
WHAT SORTS OF GENES CAN BE TUMOUR SUPPRESSOR GENES?
Signalling Smad4, DCC, APC
Transcription WT-1, p53
Gene Expression VHL
Cell Cycle Control pRb, p53
Cell Adhesion E-cadherin
Cytoskeletal Architecture NF-2
DNA Damage and Repair p53, ATMBRCA1, BRCA2
One single oncogene will not cause cancer – cooperativity
Cooperating oncogenesin mice-
Land H et al., (1983) Nature 304, 596-602; Ruley HE (1983) Nature 304, 602-606.
•cumulative effect of carcinogens
•cumulative effect of mutations
Causes of Cancer - Age
•age-related metabolic / hormonal changes
• reduced ability to repair DNA
•viruses- eg. human papilloma virus cervical cancer
• ionising radiation
Causes of Cancer - Environmental
- eg. 131I thyroid cancer post-Chernobyl- eg. UV radiation skin cancer
- eg. arsenic in tobacco smoke lung cancer
•chemicals in food / environment
CellGrowth
CellDeath
Normal Cells
Normal tissues balance cell growth with cell death.
Cell
GrowthCell
Death
Tumour Cells
In cancer this balance is disrupted.
Acquired Characteristics of Cancer
1. Limitless replication capacity2. Evasion of apoptosis3. Self-sufficiency of growth signals4. Insensitivity to growth inhibitory signals5. Tissue invasion and metastasis6. Sustained angiogenesisFrom:Hanahan D and Weinberg RA(2000) The hallmarks of cancer. Cell 100:57-70
47
Is there hope for the future? Yes – definitely!
Cancer Prevention
Novel Therapeutics
Molecular Diagnostics
Cancer Genetics
Normal Cells
Initiation(tumourigenesis)
Normal Growth
Persistent cell clone
Single transformed
celldysregulated growth
Progressive Nature of Cancer
chemicals, viruses, radiation
Promotion(smoking, free
radicals, radiation)
Progressive Nature of Cancer (2)
dysregulated growth - progressive mutations, persistence of
tumour cell subclones, enhanced blood supply
Dysplasia
further growth - mutations, production of tissue-modelling enzymes, enhanced blood supply
Invasive Tumour Metastasis
Benign Tumour
Carcinoma in situ