http://www.joomag.com/magazine/ntu-undergraduates-research-april-2014-biosciences/0163496001398433142
Above is the link for the project abstracts in our year, (mine is on page 115!) enjoy! :)
Sunday 27 April 2014
Tumour Pathology
Tumour Pathology
Cancer is a general term for over 200 diseases, used to indicate the presence of malignant neoplasms (abnormal mass of tissue). These can be characterised by the rapid and uncontrollable division of cells forming malignant tumours, whom can invade and destroy healthy tissues, and whom also persist in the same manner even when the primary stimulus causing the abnormal growth is removed. These cells have the ability to spread via invasion or implantation.
Cancer has six main hallmarks, these are:
Cancer is a general term for over 200 diseases, used to indicate the presence of malignant neoplasms (abnormal mass of tissue). These can be characterised by the rapid and uncontrollable division of cells forming malignant tumours, whom can invade and destroy healthy tissues, and whom also persist in the same manner even when the primary stimulus causing the abnormal growth is removed. These cells have the ability to spread via invasion or implantation.
- Invasion: direct growth into tissue adjacent to the tumour.
- Implantation: growth in distant sites caused via metastasis
A tumour can be defined as any unknown lump or tissue, and can be benign of malignant.
- Benign: non-cancerous mass of localised cells which will not spread.
- Malignant: cancerous mass of cells which can spread invasively to nearby tissues (known as malignant) or to distant tissues (known as metastatic).
- Neoplasm: swelling or lump comprised of an abnormal proliferation of cells, whom are no longer under normal physiological control, of uncertain origin. The ratio of proliferation to apoptosis favours the first. Neo - new, plasma - that which is formed.
Carcinoma
Carcinoma is essentially another name for cancer, referring to a malignant tumour of epithelial origin.
Carcinoma is essentially another name for cancer, referring to a malignant tumour of epithelial origin.
This would be a tumour located in the epithelial cell layers which cover body surfaces and line the organs. Carcinomas approximately make up 80% of all cancers. Common examples would be:
- Skin
- Gut
- Breasts
- Prostate
Cancer has six main hallmarks, these are:
- Avoidance of apoptosis
- Self-sufficiency of growth signals
- Insensitivity to anti-growth signals
- Limitless replication potential
- Tissue invasion and metastasis
- Sustained angiogenesis
- Deregulation of cellular energetics
- Avoiding immune destruction
- Mutation and instability of the genome
- Tumour-promiting inflammation
Another interesting trend is the difference in the types of cancers commonly found in children in comparison to adults in 2004. In adults, 54% of cancers were derived of breast, lung, bowel and prostate cancers, whereas in children, 56% of cancers were derived of leukaemias, lymphomas and CNS/brain cancers. These findings, in my opinion, show that life style and age have a severe determining factor with adult cancers. Lung cancer is a good example of this, making up 13% of adult cancers, this will be due to the presence of smoking within the population, and the abundance of asbestos which would have been inhaled in the past couple of decades.
Cancer stages
Diagnosis of the tumour will then allow for it's prognosis, allowing to predict the tumours future activity, such as:
A benign tumour tends to be well circumscribed, can be encapsulated, is slow growing, resembles the tissue of origin and will push other tissues aside, in comparison to a malignant tumour, where there is infiltrative growth, no capsule, and will cause destruction of other tissues.
Malignant tumours
Those derived from epithelial cells, from any of the 3 germ layers, are referred to as carcinomas. A carcinoma with a glandular growth pattern would be referred to as an adenocarcinoma. Carcinomas producing squamous cells are referred to as squamous cell carcinoma. It's also general practice to mention the organ of origin, e.g renal cell adenocarcinoma. Those composed of undifferentiated unknown tissue origin, are referred to as poorly differentiated or undifferentiated malignant tumour.
Many tumours are a result of chromosomal translocations, this is an abnormal rearrangement between non homologous chromosomes, where a part of one detaches, and reattaches to another, examples of these are lymphomas, such as follicular, mantle cell, Burkitt's, and MALT.
Soft tissue sarcomas
Typically rare, only an estimated 1,300 people diagnosed per year in the UK. Occur in muscle, fat, blood vessels or any organ that supports, protects and surrounds the organs. Soft tissues of the body are referred to as mesenchyma tissues, thus sarcomas being referred to mesenchymal tumours. Generally these occur in those over 30, however some do occur in young persons. Almost half occur in the limbs, mainly near the knee joint. The chest, abdomen and pelvis are common areas. Less common are the head and neck.
Blue small round cell tumours
Small blue round cells are typically found in children and young adults with cancer, the cancers are similar in their histological features, however their diagnosis is essential as their prognosis and treatment can differ greatly. The use of karyotyping (establishing the number of chromosomes and their appearance) will provide very specific information, however in order to do this, cells must be cultured. The use of FISH would be useful.
Karyotyping
Cells which have been grown within a culture are arrested during metaphase using colchicine, they'e then placed in hypotonic solution to make them swell, and are then fixed in methanol-acetic acid. Once fixed they're placed onto slides to create metaphase spreads, and their chromosomes can be stained to create the characteristic coloured bands. An example of such a stain is "G banding", this works by the use of trypsin partially digesting histone proteins, allowing the chromosome to relax and the dye to attach itself to the exposed DNA, in this case dense A&T regions. The size and location of these bands allow cytogenetics to compare and distinguish homologous chromosome pairs. This process is extremely specific but is not cost or time effective.
In Situ Hybridisation
This is a method of localising mRNA and DNA within a cell by the hybridisation of the sequence of interest via the use of a complementary nucleotide probe. This is a morphological technique and does not cause destruction of the tissue. It's detection level is 10-20 copies per cell. The sequence of interest can range in size, from 20bp long up to 1000 bp long. It's useful for untranslated or secreted proteins. It avoids the problems of anything with shared epitopes as it's very specific. There are 5 types of probes:
Originally probes were labelled with biotin, however it has recently been discovered that endogenous biotin exists within some tissues, thus a different label is now used, such as digoxigenin (Dig) or fluorescein. The Abs for these labels are made with reporter systems attached, such as alkaline phosphatase. The advent of fluorescent labels has allowed the visualisation of multiple probes simultaneously, and resulted in the development of the FISH technique. Once only applied to metaphase chromosome spreads, it can now be used on interphase cells (interphase cytogenetics).
Benign neoplasm features
Benign tumours have specific characteristics, they:
Malignant tumours have specific characteristics, they:
Pleomorphism: variation of size and shape of cells located within a neoplasm. Mitoses on their own are not a sign of malignancy, however the presence of abnormal mitoses are, and these alongside the presence of pleomorphism and hyperchromatism (development of excess chromatin) definitely favours malignancy.
Ki 67 is a protein associated with cellular proliferation. It is found only in cells which are carrying out the cell cycle, and is brought to the surface during mitosis, however in resting cells it is not present.
Carcinoma of unknown origin
Some diagnostic techniques for malignancies can fail to determine the primary origin site where the cancer developed, if the cancer has carried out metastasis. This is referred to as carcinoma of unknown primary origin (CUPO) or occult primary malignancy. In 2007, 32,100 people (roughly 50:50 gender ratio) were diagnosed with unspecified primary cancers. In post mortem examination, 15-25% still could not be identified. This is a problem as the primary site of the cancer in most cases decides the treatment and prognosis.
The majority of CUPO are adenocarcinomas or undifferentiated tumours,however it is possible they are squamous cell carcinomas, melanomas, sarcomas or neuroendocrine tumours.
Cellular differentiation
Tumours can be "graded" on how closely they imitate parent tissues which they originate from:
TNM
This is a system for determining the anatomical extent of a disease based on the assessment of 3 components:
Both grading and staging have prognostic value, but the staging is the most valuable as it indicates extent of the disease.
- Transformation stage: Single normal cell mutates into a single tumour cell
- Progression: Tumour cell replicates, and cellular variants begin to emerge, after 30 "doublings" the mass is around 1 gram in weight and contains 10^9 amount of cells. This is also known as the smallest clinically detectable mass. These cells are now mutating and becoming genetically unstable, forming different cancer cell types. Small metastases may be found in other organs. After another 10 doublings, the tumour has increased in weight to 1 kilogram, consisting of 10^12 cells, this size is considered the maximum size compatible with life. At this stage the varying cancer cells with have caused heterogeneity of the tumour. Large metastases will be present in other organs.
- Non-antigenic
- Invasive
- Metastatic
- Some will require fewer growth factors to carry out mitosis.
Neoplasia
Growth of a cancer. Size is usually bearing on no biologic behaviour. It can have varying growth configurations, such as:
Growth of a cancer. Size is usually bearing on no biologic behaviour. It can have varying growth configurations, such as:
- Infiltration and projection onto the surface
- Infiltration and ulceration of the surface
- Infiltration forming tumour mass
- Papillary
- Cauliflower appearance
- Nodular
- Lobular
- Cystic
Varying amounts of proliferating neoplastic cells and supportive stroma give tumours their excessive features.
Diagnosis of the tumour will then allow for it's prognosis, allowing to predict the tumours future activity, such as:
- Mode of spread
- Therapy response
- Genetic implications
Benign tumours
As a general rule, if -oma is a suffix then the tumour is benign, however there are exceptions, such as lymphoma, carcinoma.
The prefix coincides with the growth type, e.g:
- Adenoma (glandular)
- Papilloma (finger like)
- Cystadenoma (Cystic)
- Polp (Mucosal projection)
- Combined features such as papillary cystadenoma
A benign tumour tends to be well circumscribed, can be encapsulated, is slow growing, resembles the tissue of origin and will push other tissues aside, in comparison to a malignant tumour, where there is infiltrative growth, no capsule, and will cause destruction of other tissues.
Malignant tumours
Those derived from epithelial cells, from any of the 3 germ layers, are referred to as carcinomas. A carcinoma with a glandular growth pattern would be referred to as an adenocarcinoma. Carcinomas producing squamous cells are referred to as squamous cell carcinoma. It's also general practice to mention the organ of origin, e.g renal cell adenocarcinoma. Those composed of undifferentiated unknown tissue origin, are referred to as poorly differentiated or undifferentiated malignant tumour.
Many tumours are a result of chromosomal translocations, this is an abnormal rearrangement between non homologous chromosomes, where a part of one detaches, and reattaches to another, examples of these are lymphomas, such as follicular, mantle cell, Burkitt's, and MALT.
Soft tissue sarcomas
Typically rare, only an estimated 1,300 people diagnosed per year in the UK. Occur in muscle, fat, blood vessels or any organ that supports, protects and surrounds the organs. Soft tissues of the body are referred to as mesenchyma tissues, thus sarcomas being referred to mesenchymal tumours. Generally these occur in those over 30, however some do occur in young persons. Almost half occur in the limbs, mainly near the knee joint. The chest, abdomen and pelvis are common areas. Less common are the head and neck.
Blue small round cell tumours
Small blue round cells are typically found in children and young adults with cancer, the cancers are similar in their histological features, however their diagnosis is essential as their prognosis and treatment can differ greatly. The use of karyotyping (establishing the number of chromosomes and their appearance) will provide very specific information, however in order to do this, cells must be cultured. The use of FISH would be useful.
Karyotyping
Cells which have been grown within a culture are arrested during metaphase using colchicine, they'e then placed in hypotonic solution to make them swell, and are then fixed in methanol-acetic acid. Once fixed they're placed onto slides to create metaphase spreads, and their chromosomes can be stained to create the characteristic coloured bands. An example of such a stain is "G banding", this works by the use of trypsin partially digesting histone proteins, allowing the chromosome to relax and the dye to attach itself to the exposed DNA, in this case dense A&T regions. The size and location of these bands allow cytogenetics to compare and distinguish homologous chromosome pairs. This process is extremely specific but is not cost or time effective.
In Situ Hybridisation
This is a method of localising mRNA and DNA within a cell by the hybridisation of the sequence of interest via the use of a complementary nucleotide probe. This is a morphological technique and does not cause destruction of the tissue. It's detection level is 10-20 copies per cell. The sequence of interest can range in size, from 20bp long up to 1000 bp long. It's useful for untranslated or secreted proteins. It avoids the problems of anything with shared epitopes as it's very specific. There are 5 types of probes:
- Double stranded DNA: can be produced within bacteria via the use of plasmids, or through PCR, it has to be denatured to allow hybridisation with DNA or mRNA. They are possible to be produced in bulk, however when done so there is a risk of them re-annealing to themselves. If they're large, they may have problems when attempting to access the cell.
- Single stranded DNA: around 200-500bp in length. Can be produced via the process of reverse transcription of mRNA, or via asymmetric PCR using one primer.
- Riboprobes: these have an advantage as RNA-RNA hybrids are very strong, and are also resistant to digestion by RNases, thus post hybridisation washing with RNase can remove non-hybridised RNA and give a very clear background. These probes are hard to produce by in vitro transcription of a linearised plasmid, with an RNA polymerase from a promoter site which can produce either sense or antisense probes.
- Oligonucleotides: produced synthetically as in PCR primers, usually around 20-40bp in length. Their size is ideal for penetrating cells, however they do cover less of the target, so they're usually mixed into a cocktail in order to increase sensitivity.
- PNA probes: mimics DNA, however it has a repeating backbone of N-(2 aminomethyl)-glycine unites linked by amide bonds, The bases are attached to the backbone via methylene carbonyl linkage. It cannot be used as a PCR primer.
Originally probes were labelled with biotin, however it has recently been discovered that endogenous biotin exists within some tissues, thus a different label is now used, such as digoxigenin (Dig) or fluorescein. The Abs for these labels are made with reporter systems attached, such as alkaline phosphatase. The advent of fluorescent labels has allowed the visualisation of multiple probes simultaneously, and resulted in the development of the FISH technique. Once only applied to metaphase chromosome spreads, it can now be used on interphase cells (interphase cytogenetics).
Benign neoplasm features
Benign tumours have specific characteristics, they:
- Grow slowly
- Are encapsulated within a fibrous capsule
- Have a smooth surface
- Compress surrounding organs and tissues, pushes them to the side
- Small in size (usually)
- Do not cause death unless occurring in the central nervous system, or compressing vital organs
- Cells are very differentiated, thus resemble the tissue of origin
- Cells are uniform and almost identical
- Blood vessels around the tumour are well formed
- Doesn't have necrosis
- Doesn't metastasise
- DNA content is normal
- Karyotype is normal
Malignant tumours have specific characteristics, they:
- Grow rapidly
- Do not have a capsule
- Have an irregular surface
- Tumour invades and destroys surrounding tissue
- Large in size (usually)
- Causes death if not treated
- Cells are not very well differentiated, especially in comparison to benign tumours
- Malignant neoplasms mostly do not resemble origin tissue
- Cellular nuclei can be enlarged and hyperchromatic (darker nucleus)
- Numerous prominent nucleoli
- Cellular pleomorphism
- Increased mitotic activity with abnormal mitotic figure
- Blood vessels surrounding the neoplasm are numerous and poorly formed, some do not have any endothelial lining, and this can leads to tissue haemorrhaging
- Necrosis is present
- Metastasis does occur
- DNA content of the cells tends to be increased, additional chromosomes can be present
- Karyotyping abnormalities such as aneuploidy and polyploidy occur.
Pleomorphism: variation of size and shape of cells located within a neoplasm. Mitoses on their own are not a sign of malignancy, however the presence of abnormal mitoses are, and these alongside the presence of pleomorphism and hyperchromatism (development of excess chromatin) definitely favours malignancy.
Ki 67 is a protein associated with cellular proliferation. It is found only in cells which are carrying out the cell cycle, and is brought to the surface during mitosis, however in resting cells it is not present.
Carcinoma of unknown origin
Some diagnostic techniques for malignancies can fail to determine the primary origin site where the cancer developed, if the cancer has carried out metastasis. This is referred to as carcinoma of unknown primary origin (CUPO) or occult primary malignancy. In 2007, 32,100 people (roughly 50:50 gender ratio) were diagnosed with unspecified primary cancers. In post mortem examination, 15-25% still could not be identified. This is a problem as the primary site of the cancer in most cases decides the treatment and prognosis.
The majority of CUPO are adenocarcinomas or undifferentiated tumours,however it is possible they are squamous cell carcinomas, melanomas, sarcomas or neuroendocrine tumours.
Cellular differentiation
Tumours can be "graded" on how closely they imitate parent tissues which they originate from:
- Well-differentiated: the cells are very similar in both appearance and conformation to the tissue of origin
- Poorly-differentiated: the cells only show minimal resemblance's to the normal parent tissue
- Anaplastic: tumour shows no obvious similarities to the origin tissue, this type is associated with having aggressive behaviour.
The grading is based upon the appearance of the cells under a light microscope along with H&E staining. A higher grades means a smaller degree of differentiation, thus the worse the biological behaviour. Most systems have 3 or 4 grades:
- Grade 1: Well differentiated
- Grade 2: Moderately differentiated
- Grade 3: Poorly differentiated
- Grade 4: Anaplastic
Functional differentiation
Well differentiated tumours produce the normal product of the origin tissue, however poorly differentiated tumours are less likely to carry out the standard functions. This differentiation provides clues as to the clinical aggressiveness of the tumour. Tumours can lose their differentiation features over time as they become more malignant, and acquire more genetic mutations. The level of differentiation within the cells depict how they will respond to certain therapies and treatments.
Spreading pathways
There are different pathways taken during metastasis of malignant cells:
- Lymphatic spread: usual route for carcinomas, involves the lymph nodes
- Haematogenous spread: usual route for late stage carcinomas
- Transcoelomic (body cavity) spread: seeding of cavities surfaces by tumour, typical in ovarian carcinomas
TNM
This is a system for determining the anatomical extent of a disease based on the assessment of 3 components:
- T: the extent of the primary tumour
- N: the presence or absence and extent of regional lymph node metastasis
- M: the presence of absence of distant metastasis.
The addition of numbers to these 3 components indicates the extent of the malignant disease. The system is a shorthand notation for describing the extent of a particular malignant tumour:
TX - Primary tumout cannot be assessed
T0 - No evidence of primary tumout
Tis - Carcinoma in situ
T1,2,3,4 - Increasing size and/or local extent of primary tumour
NX - Regional lymph nodes cannot be assessed
N0 - No regional lymph node metastasis
N1 - Regional lymph node metastasis
MX - Distant metastasis cannot be assessed
M0 - No distant metastasis
M1 - Distant metastasis
Both grading and staging have prognostic value, but the staging is the most valuable as it indicates extent of the disease.
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