Hyperplasia (or "hypergenesis") is a general term for an abnormal increase in the amount of the cells of an organ or tissue causing it to increase in size. It may be due by any number of causes including (but not limited to) chronic inflammatory response, hormonal dysfunctions, or neoplasia.

Some of the more commonly-known forms of hyperplasia, or conditions leading to hyperplasia, are:

• Congenital adrenal hyperplasia. The Adrenal Hyperplasia Network provides an overview of this disease.

• Polycystic ovary syndrome. The amenorrhea/oligomenorrhea associated with this syndrome results in hyperplasia of the endometrium, or inner lining of the uterus. If left untreated, this can lead to endometrial cancer. Hyperestrinism produces the glandular and stromal proliferation in endometrium. There are three types of endometrial hyperplasia: simple hyperplasia (cystic hyperplasia), adenomatous (complex) hyperplasia and atypical adenomatous (complex atypical) hyperplasia. These types are associated with variable risk of malignant change. Grossly, the endometrium is thicker. Microscopically, in simple hyperplasia the proliferated epithelium is normal appearing (columnar, unistratified or cuboidal, if the glands are cystic dilated - cystic "Swiss cheese" hyperplasia) 1. This type is has no increased risk of malignancy. The complex hyperplasia is characterized by crowded and irregular glands. There is a low risk of malignant transformation (10%). Complex atypical hyperplasia of endometrium, also called intraendometrial neoplasia, presents architectural and cytological atypia in a reduced stroma. There is a higher risk of malignant transformation (about 25% after three years).

• Benign prostatic hyperplasia, also known as prostate enlargement. (For more information, refer to Prostate Enlargement: Benign Prostatic Hyperplasia)

• Hyperplasia of the breast. Types of breast hyperplasia are:
  • benign ductal or lobular hyperplasia - increased growth in size and/or number of cells in breast ducts or lobes, but generally does not indicate an increased risk of breast cancer
  • atypical ductal or lobular hyperplasia - increased growth in size and/or number of cells in breast ducts or lobes that develops in an unusual pattern, and can indicate an increased risk of breast cancer. A regular follow-up program is recommended.
  • lobular carcinoma in situ, or LCIS - a form of atypical lobular hyperplasia where the cell changes in the lobes are very unusual. It presents a risk of breast cancer in the future. A regular follow-up program is highly recommended; also, a specialist may wish to discuss the option of surgery with a woman having this form of breast hyperplasia.

• Focal epithelial hyperplasia (also known as Heck's disease). This is a wart-like growth in the mucous tissues of the mouth or, rarely, throat that is caused by certain sub-types of the human papillomavirus (HPV). Heck's disease has not been known to cause cancer. (For more information, refer to Focal Epithelial Hyperplasia at the Maxillo Facial Center)

• Sebaceous hyperplasia - a condition where small yellowish growths develop on the skin, usually on the face. This condition is neither contagious nor dangerous. (For more information, refer to Sebaceous Hyperplasia and Fordyce's Condition at The Skin Site)