Reactive, regenerative or reparative squamous epithelium (for example in response to trauma, inflammation, irradiation or ulceration) may manifest atypical cytology or architectural disturbance. Nutritional deficiencies such as iron, folate, and vitamin B12, can also simulate dysplasia. Such lesions are not considered precursor lesions and should be distinguished from them. Clinical history is helpful, and morphologic changes suggestive of the inciting event (e.g. ulceration, inflammation, haemorrhage, radiation-induced mesenchymal and/or endothelial nuclear enlargement and hyperchromasia) may be present. The epithelial changes in these cases are generally less pronounced than in severe dysplasia/atypical hyperplasia or CIS, atypical mitoses are almost never present, and the epithelium may be thinned, or, if thickened, stratification and maturation often develop as the regenerative/ reparative process matures.
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