Oncology Notes

Oncology

1. Introduction

A neoplasm is the abnormal proliferation of cells. It can be defined as a new growth of cells, originally derived from normal tissues, which have undergone heritable genetic changes that have made them relatively unresponsive to growth controls and to expand beyond their normal anatomic boundaries.

Neoplasms may be benign or malignant. Whilst a tumour may be either benign or malignant, cancer always refers to malignant neoplasms.

Oncology is the study of neoplasia.

Benign tumours do not invade the surrounding tissue or spread around the body and so are usually curable. Malignant tumours, if left untreated, can invade the site of location and spread to new sites around the body – metastasis.

Pre-neoplastic changes can be diagnostically important. These include hyperplasia (increased cell number in a tissue), metaplasia (transformation of one differentiated cell type to another) and dysplasia (abnormal pattern of cell growth).Hyperplasia must be differentiated from hypertrophy, which is an increase in size of individual cells. Pre-neoplastic changes are usually reversible and are physiological responses to injury, irritation or increased demands.

2. Nomenclature

Most tumours consist of a single cell type. The name of the neoplasm reflects the cell type from which the tumour has arisen.

Benign tumours that have arisen from mesenchymal cells are given the suffix –oma. Malignant tumours of mesenchymal origin are -sarcomas. A prefix indicates the tissue of origin. For example, a lipoma is a benign tumour derived from a lipocyte, whereas a liposarcoma is a malignant tumour derived from a lipocyte. The cells of the haematopoietic system are mesenchymal. Tumours arising from blood cells or their precursors are called leukaemia. Neoplastic haematopoietic cells are usually found in large numbers in the blood stream, but may also form solid masses.

Benign tumours arising from nervous tissue also are given the suffix –oma, for example astrocytoma arising from astrocyte cells. The word malignant is added to describe malignant tumours.

Benign tumours arising from glandular epiethelium are termed adenomas. This term is also used to describe tumours that have not arisen from glandular epithelium but that have a tubular appearance, such as renal adenomas. Malignant tumours arising from the glandular epithelium are adenocarcinomas.

Benign tumours arising from protective epithelium are termed papillomas. Malignant tumours of epithelial origin are called carcinoma. Prefixes may be added to further describe the tumour.

Carcinomas or adenocarcinomas that cause excessive collagen formation in the surrounding tissue are called scirrhous.

For BSAVA full list of tumour nomenclature see: file:///C:/Users/user/Documents/Year%203/Principles%20of%20Clinical%20Veterinary%20Science/Week%202/Reading%20-%20Nomenclature%20of%20neoplasms.pdf

3. Tumour grading

Grading schemes indicate how similar or dissimilar a neoplasm is to normal tissue. Tumour grade is strongly linked to prognosis and response to therapy. Grading schemes evaluate the degree of differentiation of tumour cells. Grade I is well differentiated, Grad II is moderately differentiated and Grad III is poorly differentiated.

The TMN system classifies tumours according to the size of the primary tumour (T), the degree of lymph node involvement (N) and the extent of metastasis (M). It is as follows:

• T0 indicates carcinoma in situ

• T1-4 the indicate size of the primary tumour. The characteristics of this description vary depending on the type of tumour.

• N0 indicates no lymph node involvement.

• N1 indicates regional lymph node involvement

• N2 indicates distant lymph node involvement.

• M0 indicates there is no detectable metastasis.

• M1 indicates there is a secondary tumour in the same organ or cavity.

• M2 indicates there is distant metastasis.

4. Benign versus malignant tumours

Anaplastic cells are poorly differentiated cells that exhibit notable cellular and nuclear pleomorphism (variation in size and shape). Anaplastic nuclei are often:

• Hyperchromatic (very dark staining) because of increased DNA content.

• Disproportionately large compared to cell size

• Have prominent nucleoli.

Mitotic figures appear as darkly staining figures histologically.

5. Tumour growth

The latent period is the time before the tumour becomes clinically detectable. Masses become detectable at around 1cm in size and contain around 10⁹ cells, a result of around 30 rounds of replication. This means by the time tumours are clinically detectable they have been developing the host for many years in the latent form.

Many neoplastic cells no longer respond to extrinsic cell signals directing them to G₀ (the quiescent state of the cell cycle) or express functional p53 (tumour suppressor gene product that gives cells time to repair damaged DNA by initiating cell-cycle arrest). As such they are insensitive to anti-growth signals, and are self-sufficient in growth signals. They have limitless replicative potential. Many cancer cells are also resistant to apoptosis.

Genomic instability is a classic characteristic of cancer.

Tumour growth begins with inititation, the introduction of an irreversible genetic change in cells by the action of a mutagenic agent or initiator. Mutagenic agents or initiators are physical or chemical carcinogens that damage...

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