Hyperplasia corresponds to an increase in the number of cells in an organ or tissue, which can result in the formation of a benign neoplasm or in the enlargement of that organ. In other cases, hyperplasia can only be seen under a microscope.
An example of normal (or physiological) hyperplasia is the increase in milk-producing mammary cells in response to pregnancy. An example of hyperplasia causing organ enlargement is benign prostatic hyperplasia, which occurs in about 50% of men around the age of 50. Another example of hyperplasia is that which affects the endometrium, which is the inner lining tissue of the uterus.
Endometrial hyperplasia can be caused, for example, by the administration of hormone therapy with tamoxifen, increasing the risk of developing endometrial cancer.
