Neoplasia 1 Flashcards
Where is the word neoplasia derived from?
Greek - ‘neo’ = new, ‘plasia’ = growth or formation
Definition of neoplasia
uncoordinated growth of cells that persists after the initial stimulus is removed
Description of normal cell growth
coordinated, controlled, responsive to stimuli, self-limiting, well-differentiated
Description of neoplastic growth
autonomous growth that escapes normal regulatory mechanisms
What is the result of neoplasia?
abnormal tissue masses (tumours/neoplasms)
What are the 2 types of neoplasia?
benign or malignant
What are the cells of benign neoplasms like?
well-differentiated cells that resemble the tissue of origin (e.g. if benign neoplasm is in epithelia, cells look like epithelial cells)
What is the growth rate of benign neoplasms?
slow growth
Metastasis definition
the spread of cancer cells from the primary tumour site to other parts of the body (via circulatory/lymphatic system)
Can benign neoplasms metastasise?
no metastasis - local expansion rather than invasion
What structural feature of benign neoplasms prevent invasion of surrounding tissue?
the borders are well defined - often encapsulated
Are benign neoplasms life-threatening?
no unless in critical location
Examples of benign neoplasms in oral cavity
fibroma, lipoma, papilloma
What are the cells of malignant neoplasms like?
often poorly differentiated and variable/poor histological resemblance to normal tissue (look like stem cells rather than original tissue)
What is the growth rate of malignant neoplasms?
rapid, uncontrolled growth
Can malignant neoplasms metastasise?
yes due to poorly defined borders
What does the absence of defined borders in malignant neoplasm allow?
Enables infiltrative growth and invasion of surrounding tissue
Can malignant neoplasms be life-threatening?
malignant neoplasms are often fatal is untreated
Is there a potential for recurrence after removing a benign neoplasm?
No - benign tumours are encapsulated so all the cells are removed
Is there a potential for recurrence after removing a benign neoplasm?
yes - cells may escape removal and reform tumour
Examples of malignant neoplasms in the oral cavity
squamous cell carcinoma, mucoepidermoid carcinoma, salivary gland carcinoma
What is the frequency of necrosis occurring in benign neoplasms?
rarely occurs
What is the frequency of necrosis occurring in malignant neoplasms?
common
Which type of neoplasm commonly exhibits ulceration?
malignant neoplasm (rare in benign)
Where does ulceration commonly occur in malignant neoplasms?
skin or mucosal surfaces
What is the direction of benign neoplastic growth on skin or mucosal surfaces?
often exophytic (projects outwards from surface - lump/ulcer may be present)
What is the direction of malignant neoplastic growth on skin or mucosal surfaces?
often endophytic (invades inwards)
Anaplasia definition
loss of cellular differentiation and reversion to a more primitive, stem-cell like form that often has an increased capacity for rapid cell division
Which type of neoplasia has anaplastic cells?
malignant neoplasms
What changes do malignant cells undergo?
anaplasia, nuclear changes and cellular changes
What are the nuclear changes that malignant cells undergo?
enlarged nuclei (high nucleus : cytoplasm ratio), hyperchromasia (so darkly staining), abnormal chromatin pattern, prominent nucleoli
What cellular changes occur in malignant cells?
pleomorphism, abnormal mitotic figures, loss of polarity
Pleomorphism definition
variation in size and shape (of cell/nuclei)
What feature of a cell when disrupted can lead to loss of polarity?
cytoskeleton (maintains cell shape and structure)
Cell polarity definition
the intrinsic asymmetry observed in cells (shape, structure, cellular organisation)
What is the importance of cell polarity in epithelial cells?
cell polarity allows the formation of defined apical and basal membranes in epithelial cells
What process is loss of cell polarity often associated with?
epithelial-to-mesenchymal transition (EMT)
What happens during epithelial-to-mesenchymal transition (EMT)?
epithelial cells lose their polarity and acquire mesenchymal characteristics which promotes cell migration and invasion
How are benign tumours named?
cell/tissue of origin + suffix ‘-oma’
How are malignant tumours named?
cell/tissue of origin + either carcinoma / sarcoma
When would a malignant neoplasm have ‘carcinoma’ as a suffix?
if the malignancy is of epithelial origin
When would a malignant neoplasm have ‘sarcoma’ as a suffix?
if the malignancy is of mesenchymal origin
Name of benign neoplasm of surface epithelium
papilloma
Name of malignant neoplasm of surface epithelium
squamous cell carcinoma
Name of benign neoplasm of glandular epithelium
adenoma
Name of malignant neoplasm of glandular epithelium
adenocarcinoma
Name of benign neoplasm of fibrous tissue
fibroma
Name of malignant neoplasm of fibrous tissue
fibrosarcoma (connective tissue is of mesenchymal origin)
Name of benign neoplasm of adipose tissue
lipoma
Name of malignant neoplasm of adipose tissue
liposarcoma
Name of benign neoplasm of cartilage
chondroma
Name of malignant neoplasm of cartilage
chondrosarcoma
Name of benign neoplasm of bone
osteoma
Name of malignant neoplasm of bone
osteosarcoma
Where are epithelial tumours derived from?
epithelial tissues
Examples of epithelial tumours
squamous cell carcinoma, basal cell carcinoma
Where are mesenchymal tumours derived from?
connective tissues
Examples of mesenchymal tumours
osteosarcoma, chondrosarcoma, liposarcoma
Where are hematopoietic tumours derived from?
blood forming tissues
Examples of hematopoietic tumours
leukaemia, lymphoma
Where are neural tumours derived from?
Neural tissues
Examples of neural tumours
neurofibroma, schwannoma
Where are mixed tumours derived from?
more than one tissue type
Example of mixed tumour
pleomorphic adenoma of salivary glands
What are the different types of genetic alterations?
point mutations, chromosomal translocations, gene amplifications, deletions
What happens during a point mutation?
one nucleotide/base is swapped
What happens during chromosomal translocations?
part of a chromosome breaks and is reattached to a different chromosome (can lead to overexpression)
What happens during gene amplifications?
multiple copies of a gene is produced (leads to overexpression)
What does the accumulation of genetic alterations result in?
uncontrolled proliferation, resistance to apoptosis, ability to invade and metastasise
What are the key genes that can lead to cancer if affected?
DNA repair genes, oncogenes, tumour suppressor genes
Definition of oncogenes
genes that promote cell growth and division
How do oncogenes exist initially before they are overexpressed/mutated?
proto-oncogenes
What are proto-oncogenes?
normal cellular genes that regulate cell growth
What are the main functions of oncogenes?
promote cellular proliferation, survival and migration
What are the mechanisms that activate oncogenes from proto-oncogenes?
chromosomal translocation, point mutations, gene amplification, insertion of promoter/enhancer
How may chromosomal translocation of the oncogene cause its activation?
the oncogene can be translocated from an untranscribed site to a position adjacent to an actively transcribed gene (e.g. Ig gene in B cell) which leads to inappropriate transcription of oncogene
Example of neoplasia where chromosomal translocation involving an oncogene is the cause
Burkitt lymphoma (increased B cells)
How can a point mutation within the oncogene lead to activation?
substitution of a single base is translated into an amino acid substitution resulting in a hyperactive oncogene
How can gene amplification of the oncogene lead to neoplasia?
multiple excess copies of the oncogene are inserted stimulating cellular proliferation
How may the insertion of a promoter/enhancer activate oncogenes?
insertion of promoter or enhancer sequence proximal to oncogene actives its expression
Examples of oncogenes (inactive in health)
RAS (signal transduction), MYC (transcription factor), HER2/neu (growth factor receptor), BCL-2 (inhibits apoptosis)
Definition of tumour suppressor genes
genes that inhibit inappropriate cell division and suppress growth
What are the functions of tumour suppressor genes?
cell cycle regulation, apoptosis induction, DNA damage repair, maintain genomic stability
How are tumour suppressor genes inactivated?
two hit hypothesis - both alleles (on both chromosomes) must be inactivated - tumour suppressor gene can still function is only one chromosome is affected
What is the consequence of tumour suppressor genes being inactivated?
loss of cell cycle control leading to uncontrolled proliferation, genomic instability
Examples of tumour suppressor genes
Tp53, RB (retinoblastoma gene)
What is the cause of DNA mutations/damage?
cariogenic stimuli
Function of TP53 gene
‘guardian of the genome’ - maintains genome stability via the synthesis of p53
What happens to cells with DNA mutations that have a normal p53?
cell is arrested in G1 until the damage is repaired or apoptosis occurs if the damage is too severe
What happens in cells that have a DNA mutation and a defective p53 (due to TP53 mutation)?
no repair or apoptosis occurs and the cell proceeds to S phase. DNA damage is propagated to daughter cells, uncontrolled proliferation to form tumour
What are retinoblastomas?
malignant tumours derived from the retina that occur almost exclusively in children
What are the two types of retinoblastomas?
inherited and sporadic retinoblastoma
Which was the first tumour suppressor gene identified?
retinoblastoma gene (RB)
What is the function of a normal retinoblastoma gene?
controls progression from G1 to S phase of cell cycle, bind and inactivates transcription factors (E2F family), prevents uncontrolled cell division
What must occur for retinoblastoma to take place?
both RB alleles must be inactivated (two-hit hypothesis)
What happens during retinoblastoma?
there is a loss of cell cycle control leading to uncontrolled proliferation
Which type of retinoblastoma is more common?
inherited retinoblastoma (one allele is already impaired)
Which type of retinoblastoma has a high risk for bilateral retinoblastoma?
inherited retinoblastoma (high possibility of at least one mutation occurring in any cell)
Which type of retinoblastoma causes unilateral retinoblastoma?
sporadic retinoblastoma
What happens in inherited retinoblastoma?
one of the paired RB1 genes is already mutated/absent. So mutation/loss of the remaining RB1 allele in any retinal cell will lead to retinoblastoma. Likely to occur more than once (high risk of bilateral retinoblastoma)
What happens in sporadic retinoblastoma?
mutations/deletions of both RB genes in the same cell or its daughters must occur (very rare and is unilateral - almost impossible for process to occur in both eyes!)
Carcinogens definition
agents that initiate or promote cancer development
What are the categories of carcinogens?
chemical, physical and biological carcinogens
Examples of chemical carcinogens
tobacco, asbestos, benzene
Examples of physical carcinogens
UV radiation, ionizing radiation
Examples of biological carcinogens
HPV, HBV, H. pylori
What tumour is associated with polycyclic aromatic hydrocarbons?
skin (mineral oil exposure) and lung cancer (smoking)
What tumour is associated with aromatic amines?
bladder cancer (in rubber and dye workers)
What tumour is associated with alkylating agents?
leukaemia
What tumour is associated with vinyl chloride?
liver angiosarcoma
Which biological carcinogen is associated with cervical and oropharyngeal carcinoma?
human papillomavirus
Which biological carcinogen is associated with nasopharyngeal cancer?
epstein-barr virus
What is carcinogenesis?
the multi-step process of cancer development
What are the steps in the theory of carcinogenesis?
- initiation
- promotion
- progression
What happens during the initiation step of carcinogenesis?
carcinogen causes an irreversible alteration in DNA (of relevant genes e.g. oncogene/tumour suppressor gene)
What happens during the promotion stage of carcinogenesis?
a promoter stimulates proliferation of initiated cells via clonal expansion to form a benign tumour (reversible process)
What happens during the progression stage of carcinogenesis?
additional mutations are acquired which increases malignant potential and develops invasive and metastatic capabilities
Definition of latency period
time between exposure to carcinogen and development of cancer
How does cellular senescence normally work?
each time a cell divides, the telomeres become shorter until the chromosome is too short and the cell can no longer divide.
What are the 3 genetic mechanisms in carcinogenesis?
- expression of telomerase
- loss/inactivation of both TSG copies
- activation of oncogenes
How does telomerase expression contribute to carcinogenesis?
telomerase prevents telomeric shortening with each cell division hence preventing cellular senescence, making the cell immortal
How does inactivation of tumour suppressor genes contribute to carcinogenesis?
the loss of TSG function permits mutations (DNA repair is impaired) and removes inhibitory growth control
How does the activation of oncogenes contribute to carcinogenesis?
results in cell proliferation via autocrine growth stimulation
Epigenetics definition
the study of changes in organisms caused by modification of gene expression rather than an altered gene code
How do epigenetic mechanisms contribute to carcinogenesis?
either normally repressed genes are abnormally expressed or normally active genes are repressed (silenced)
What are the 3 epigenetic mechanisms that contribute to carcinogenesis?
- hypermethylation
- histone modifications
- microRNA
How may hypermethylation contribute to carcinogenesis?
gene silencing results from the hypermethylation of promotor DNA sequences
How can histone modification contribute to carcinogenesis?
histone modifications usually to histone tails can alter chromatin structure leading to gene up- or downregulation
How does microRNA contribute to carcinogenesis?
increased microRNA leads to reduced mRNA translation and protein expression whereas decreased microRNA enhances protein expression
What is microRNA?
short sequences of inhibitory RNA that binds to mRNA transcripts
What are some host factors that can contribute to carcinogenesis?
race/ethnicity, diet and obesity, constitutional factors (sex, inherited risks..), transplacental exposure, premalignant lesions
What are premalignant lesions of the oral cavity referred to as?
Oral Potential Malignant Disorders (OPMD)
Examples of premalignant lesions of the oral cavity
leukoplakia, erythroplakia, oral submucous fibrosis
Definition of leukoplakia
white patch that cannot be characterised clinically or pathologically as any other disease
What is the malignant transformation rate of leukoplakia?
3-17%
Definition of erythroplakia
red patch that cannot be characterised clinically or pathologically as any other disease
What is the malignant transformation rate of erythroplakia?
14-50%
What is oral submucous fibrosis characterised by?
fibrosis and restricted mouth opening
What is associated with causing oral submucous fibrosis?
areca nut/betel quid chewing
How is the risk of cancer of premalignant lesions predicted?
checking for dysplasia in biopsy of premalignant lesion
What are the factors affecting tumour growth?
cell proliferation rate, cell death rate (apoptosis), angiogenesis, stromal interactions
How does angiogenesis affect tumour growth?
blood vessels supply nutrients and oxygen, provides route for metastasis
What is the growth pattern for benign tumours?
expansile growth (pushes surrounding tissues aside, encapsulated, distinct border)
What is the growth pattern for malignant tumours?
infiltrative growth (invasion of surrounding tissues, irregular/ill-defined borders, destruction of normal architecture)
How is growth rate / aggression of a tumour estimated clinically?
using tumour doubling time
What is meant by tumour heterogeneity and clonal evolution?
diverse cell populations in tumours, selection pressures leads to emergence of aggressive clones, has implications for treatment resistance
