hyperplasias

Hyperplasia is an increase in the number of cells in a tissue or organ, leading to enlargement. It results from increased cell proliferation rather than cell enlargement (hypertrophy) and can be reversible if the stimulus is removed. Hyperplasia is not a cancer itself, but certain forms may predispose to neoplasia depending on context.

Hyperplasia can be physiologic (normal, hormone-driven) or pathologic (driven by abnormal stimuli). Physiologic hyperplasia occurs in response to hormones or growth factors, such as endometrial thickening under estrogen during the reproductive cycle, or mammary and uterine tissue changes during pregnancy. Compensatory or regenerative hyperplasia occurs after tissue loss or injury, such as hepatic hyperplasia after partial hepatectomy or kidney hyperplasia after nephrectomy.

Pathologic hyperplasia arises from persistent stimulation or irritation, such as estrogen-driven endometrial hyperplasia without progesterone counterbalance, or benign prostatic hyperplasia in aging men. Other examples include thyroid follicular hyperplasia in response to elevated TSH, and skin or mucosal hyperplasias due to chronic irritation. In many cases, the abnormal stimulus can be removed or treated to reverse hyperplasia; however, persistent hyperplasia may be associated with an increased risk of neoplasia in specific tissues (for example, endometrial hyperplasia with atypical features may progress to cancer).

Diagnosis relies on clinical context and histopathology, sometimes with imaging; management targets removing the stimulus or reducing cell proliferation. Hyperplasia contrasts with hypertrophy and metaplasia, and with neoplasia, which involves clonal cell growth and potential malignant transformation.