Epithelial hyperplasia is benign proliferative breast lesion which arising as an unexpected new growth of epithelial cells. Sometimes epithelial hyperplasia is referred to as 'intraductal breast hyperplasia' or possibly 'breast hyperplasia of the usual type'. The lesion has also commonly been referred to as 'epitheliosis'. Somtimes epithelial hyperplasia has been referred to as papillomatosis as well. Breast epithelial hyperplasia may occur within a duct, ductule, or a lobule. However, because there can be many variations in presentation, likely due to the influence of various hormones, the distinction between ductal and lobular epithelial hyperplasia can be quite subjective.
Benign epithelial hyperplasia of the breast will often appear as parallel or 'streaming' arrangment of central cells featuring indistinct cell borders. Cells will often have a granular and 'acidophilic' cytoplasm. Nuclei tend to be oval and normochromatic and with a slight overlap. Nucleoli tend to be small and indistinct. Frequently, myoepithelial cells are also present. Apocrine metaplasia may also be variably present, and one sometimes finds either intraluminal or stromal calcification. Necrosis is rare. Cell mitoses are generally either absent or extremely minimal, and there will generally be no other atypical features of any kind.
The number of 'layers' of neoplastic cells is often used as an informal means of disinguishing different degrees of hyperplasia. When there are two to four new epithelial cell layes, this might be called 'mild' hyperplasia, (which has no increased risk for breast cancer development). When there are greater than four layers the lesion might be termed 'moderate' breast hyperplasia, which does increase risk for breast cancer between 1.5 to 2 times. (This increased risk is thought to be higher for women over 50). When the new layers of neoplastic epithelial cells are so prevelant as to virtually fill the breast duct completely, the lesion might be termed 'florid' hyperplasia, which also increases risk of future breast cancer development up to two times.
It still remains unclear whether or not epithelial hyperplasia is a completely benign condition, or whether or not it may undergo malignant change into carcinoma. About 26% of cases of epithelial hyperplasia show now atypical features.
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