Tumours can be related to four basic tissue types:
♦ Nervous, or precursors of germ cells.
Benign tumours recapitulate normal cell morphology, lack invasive-ness and metastatic potential, are slowly growing, but may cause severe damage and death because they are strategically placed (e.g. CNS, larynx). Benign tumours may transform into malignant (e.g. Schwannoma).
Tumour cells proliferate autonomously, escaping to an unpredictable extent the control of hormones and growth factors. They show varying degrees of atypical morphology, in terms of degree of maturation, and differentiation. The malignant appearance (pheno-type) of cells include:
♦ Anaplasia (lack of differentiation).
♦ Cytoplasmic basophilia (increase of ribosomes).
♦ Nucleolar hypertrophy. and/or:
♦ Increase in number of the nucleoli.
♦ Increase of the mitotic index.
♦ Presence of bizarre mitotic figures.
♦ Variations in cell size and shape.
♦ Increase of nucleo-cytoplasmic ratio.
Disorderly structure and deviations from the normal tissue architecture, such as loss of polarity, are reflected in atypical growth.
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