CA05 (2010) - Question E1

Compare and contrast the natural history and biological behaviour of benign and malignant neoplasms

Curriculum Reference: Introduction to neoplasms

This question is exactly the same as the 2009 version of E1.

Comparison of Natural History

A single tumour stem cell must undergo in excess of thirty divisions before a clinically detectable mass ( > 1 gm) is formed. A further ten divisions would lead to a mass of over 1 kg, incompatible with life. This statement is only true if all the cells produced in a division survive and continue to replicate themselves. Also, the growth of tumours may also be dependent on endocrine influences. Leiomyomas of the uterus may change size dependent on the menstrual cycle, and during pregnancy may become much larger before shrinking in menopause
In general, the less differentiated a tumour is, the less restrictions it has on cell division and the rate of growth is usually faster. As malignant tumours tend to be less differentiated, they also trend towards more rapid growth. This generalisation is not always true as some benign tumours (eg. keratoacanthoma) may grow more rapidly than malignant equivalents (eg. squamous cell carcinoma of skin).
The natural history of malignant tumours includes invasion and metastasis, which are not seen in benign tumours.

Comparison of Biological Features

Benign tumours typically grow more slowly, do not infiltrate into surrounding tissues and do not metastasise to distant sites. In some locations they may still cause deleterious effects due to compression of critical structures (eg. skull base meningioma). Benign tumours are typically well differentiated, and may produce hormones or other products similar to their parent tissue.
Malignant tumours will often grow rapidly and infiltrate surrounding structures. They may also grow with a ‘pushing border’ similar to benign tumours. They can cause symptoms through direct invasion, metastatic spread or through paraneoplastic syndromes such as hypercalcaemia or cachexia.
The rate at which a tumour grows may be measured as a volume doubling time, the time taken for the tumour to double in size. This is dependent on the number of cycling cells (growth fraction, GF) and the speed of the cell cycle. By multiplying these two figures, it is possible to obtain the potential doubling time Tpot. The actual doubling time is significantly longer than the potential time due to loss of cells to senescence, necrosis or apoptosis.


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