Unit 7: Neoplasia Flashcards
what is neoplasia
excessive and disorganized cell or tissue growth that is unresponsive to normal growth control mechanisms
what is required for the normal structure of a tissue to be maintained after damage
the rate of cell proliferation must balance with the rate of differentiation (leading to cell death)
what happens if there is discrepancy between rate of cell proliferation and rate of differentiation in attempt of tissue repair
the tissue will become abnormal at both the gross and histologic levels which can lead to increase of decreased mass of the affected tissue
what is hyperplasia
- increased numbers of cells
- the main mechanism that causes increased size in organs and tissues consisting of labile and stable cell types
when does hyperplasia result
- when the cells of a tissue are stimulated to undergo mitosis
what is hypertrophy
- increased size of cells
- the only method of adaptation that can occur in tissues made up of permanent cells (cells can’t multiply)
- there is an increase in the amount of cytoplasm and the number of cytoplasmic organelles
hyperplasia vs hypertrophy
- both can be physiologic, occurring in response to an increased demand
- both are reversible if the demand is removed
- can occur together and lead to organ enlargement
- can be pathologic, without an increased demand
what is atrophy
- “waste away” as a result of degeneration of cells
why do you experience atrophy when you have a cast on
- lack of use of the muscles results in reduction in the structural components of the cell (decreased synthesis, increased catabolism or both)
atrophy is the opposite of…
hypertrophy and hyperplasia
what is the significance of decreased cell size in atrophy
- to re-establish equilibrium between cell size and reduced blood supply, nutrition or trophic stimulation
when can the term atrophy not be used to describe an organ
when it is hypoplastic (underdeveloped) or aplastic (completely undeveloped)
osteoporosis: example of disuse atrophy
- the result of bone resorption occurring more rapidly than formation
- weight-bearing exercise is important to prevent osteoporosis
what is disuse atrophy
- atrophy caused by lack of the use of muscles
- causes a rapid decrease in the size of muscle cells (fibres)
- can be reversed quick when activity is resumed
what happens if skeletal muscle fibres are lost
- only capable of limited regeneration so if fibres are lost muscle mass can only be restored by hypertrophy (increasing size) of muscle fibres - slow process
what is denervation atrophy
the result of lack of stimulation of muscle fibres by lower motor neurons
- seen in the limbs of people with spinal chord injuries
what is senile atrophy
cell loss associated with normal aging
what is pressure atrophy
atrophy as the result of ischemia due to compression of blood vessels
how can atrophy result from the lack of trophic hormones
the lack of estrogen following menopause leads to atrophy of the vaginal epithelium and endometrium
what is metaplasia
- abnormal growth resulting from abnormalities in differentiation and maturation
- the normal phenotype of mature cells is replaced by another type of mature cell which is not normal for that site
- a reversible change
what is squamous metaplasia characterized by
- non-cancerous (benign) changes in squamous cells in the epithelium
why does epithelial metaplasia occur
- ## stem cells have the potential to differentiate in different ways in response to chronic irritation
what is osseous metaplasia
- areas of bone formation seen amongst the dense, fibrous scars
does metaplasia have any clinical significance?
- generally no
- may have survival advantages
functional deficit from metaplasia of ciliated columnar epithelium of the bronchi
- infection can happen due to loss of the mucus/ciliary clearance mechanism
what happens if the influences that caused metaplasia persist?
- neoplastic transformation may occur if other factors are favourable to abnormal cell growth - squamous cell metaplasia leads to squamous cell neoplasia
what is dysplasia
- abnormality of both differentiation and maturation, primarily seen in epithelial tissue
- characterized by increased nuclear size, increased chromatin content, cytoplasmic abnormalities, increased rate of multiplication and disorderly maturation
- loss of the uniformity of individual cells
dysplasia as a premalignant lesion
- the risk of developing cancer increases with the “severity” of the dysplasia, its duration and its site
how does dysplasia differ from neoplasia
- dysplastic lesions are NON-invasive (neoplasia is) and may spontaneously revert to normal
- dysplasia may look like cancer but so not yet show evidence of invasive behaviour
what is a tumour/neoplasm
the resulting mass of abnormal tissue due to excessive and disorganized growth of cells or tissues that is unresponsive to normal growth control
what is oncology
the study of tumours
how do cancer cells differ from normal cells
- cancer cells contain genetic damage to growth-promoting proto-oncogenes and growth-suppressing cancer suppressor genes which cause them to behave abnormally
what are the 10 hallmarks of cancer
- self sufficient growth signals
- insensitivity to growth inhibitory signals
- altered cell metabolism
- evasion of cell death
- limitless potential for replication
- angiogenesis
- invasion of metastasis
- evasion of immune surveillance
- genomic instability
- tumour-promoting inflammation
which of the hallmarks of cancer are considered the 2 enabling factors
- self sufficient growth signals - proton-oncogenes are mutated to oncogenes which promote cell growth
- insensitivity to growth inhibitory signals - cancer suppressor genes are mutated and lose control of the cell cycle, allows growth of tumours and prevents their apoptosis
self sufficient growth signals - hallmark of cancer
- proto-oncogenes are mutated to oncogenes, and oncoproteins are produced which promote cell growth without external signals
insensitivity to growth inhibitory signals - hallmark of cancer
- the protein products of tumour suppressor genes are disrupted, allowing cells to become refractory to growth inhibition
- the RB cancer suppressor gene is inactivated by growth factors which allow cells to enter the S phase
- loss of normal cell cycle control
- mutations in molecules that act to inhibit cell proliferation impairs their effects
almost all cancers have disabled G1 checkpoints due to defects in…
RB, p16, cyclin D or CDK4
TP53 tumour suppression gene
- a commonly mutated gene is cancer
- has anti-proliferative effects and regulated apoptosis
- known as the “guardian of the genome”
- in cells with mutations of TP53, DNA damage does not induce cell cycle arrest or DNA repair - damaged cells proliferate and neoplasms arise
altered cell metabolism - hallmark of cancer
- Warburg effect = distinct form of metabolism displayed by cancer cells
- in cancers, oncogenic mutations involving growth factor signalling pathways and MYC deregulate normal metabolic pathways
evasion of cell death - hallmark of cancer
- mutation in any gene that regulates apoptosis prevents apoptosis of tumour cells and allows them to persist
limitless potential for replication - hallmark of cancer
- when telomeres are shortened to a certain point, cells can no longer divide effectively
- tumour cells show activation of telomerase which acts to maintain normal telomere length
- thus capable of replicating indefinitely
angiogenesis - hallmark of cancer
- tumours need blood to grow and metastasize
- tumour-associated neoangiogenic factors may be produced by tumour cells which aid in the formation of new blood vessels
- the balance between angiogenic and anti-angiogenic factors control tumour growth
invasion and metastasis - hallmark of cancer
- the appearance of new “tumour associated antigens” on surfaces of cancer cells represents expression of the altered genome
- tumour associated antigens may invoke an immune response
evasion of immune surveillance - hallmark of cancer
- cancer evades the immune system, preventing it from recognizing and destroying cancer cells
genomic instability - hallmark of cancer
- constant but rare genome instability can contribute to the development of cancer
- fosters activation of genetic mutations
tumour-promoting inflammation - hallmark of cancer
- chronic inflammation modifies the tumour environment, aiding in tumour progression
integration of cancer hallmarks
- cancer results from the accumulation of multiple mutations
- main factors in cancer development are transformation of proton-oncogenes into oncogenes and loss of function of tumour suppressor genes
tumours are heterogenous…
- mutations do not occur in all tumour cells at once, but rather in individual cells
- the rate at which these mutant subclones are generated is variable between tumour types
what are known agents that cause specific types of cancer
cigarette smoke = lung cancer
Human pappiloma virus (HPV) = cervical cancer
what are the main carcinogenic agents and why
- chemicals, radiation and viruses
- all have the ability to directly cause genetic damage
latent period of carcinogens
- “first hit” = exposure to the carcinogen
- after exposure several changes and mutations occur in the latent period
- then a tumour starts to develop