by Justin Lee

Created on: February 24, 2009   Last Updated: May 11, 2009

People commonly confuse, misinterpret, or incorrectly explain the "-plasias." Health and research journals toss the words "metaplasia," "heteroplasia," "dysplasia," "neoplasia," "hyperplasia," and "anaplasia" throughout their works, but what do these words really mean?

It is tempting for readers to lump all the "-plasias" together, assuming that they all refer to cancerous or pre-cancerous cells, but that's an erroneous assumption. Hyperplasia, metaplasia, and heteroplasia don't necessarily deal with cancer, and the other three terms cover a wide spectrum of cancer progression.

1. Hyperplasia is any abnormal multiplication of cells.

Hyperplasia refers to an abnormal increase in cellular quantity (i.e., constantly dividing cells). Hyperplastic growth in cell number usually results in organ enlargement or (benign) tumor formation, but sometimes it is noticeable only under a microscope. Hyperplasias only form benign tumors (unless further DNA damage/cellular mutations occur) because the cells of a hyperplastic growth remain subject to normal regulatory control mechanisms. This stands in contrast to neoplastic growth (the process underlying malignant tumors), in which cells replicate/proliferate in a non-physiological manner which is unresponsive to normal stimuli.

Hyperplasia may be due to a number of causes, including: increased exertion/stress (as in the case of muscle use), chronic inflammatory response, hormonal dysfunctions, or compensation for damage or disease elsewhere. Sometimes, hyperplasia is a natural response and completely normal/harmless; for instance, the growth and multiplication of milk-secreting glandular cells in the breast as a response to pregnancy is considered "hyperplastic cell growth."

Other times, however, hyperplasia can cause (non-cancerous) medical problems. If an infant consumes too much sugar in his/her first year of life, his fat cells (adipocytes) will greatly multiply in number (hyperplasia), and later in life he will be at higher risk for "hyperplastic obesity," obesity caused by an increase of the number of fat cells. This stands in contrast to "hypertrophic obesity," where a person has a normal quantity of adipocytes, but each of those fat cells is abnormally large in size.

2. Metaplasia is the transformation of one type of tissue into another.

Metaplasia ("change in form") refers to the exchanging of one type of differentiated cell type for another mature differentiated cell type. This change can be a normal physiological

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