What Do Dysplasia, Metaplasia, Atrophy, Hyperplasia and Hypertrophy Mean in Pathology Reports?

To determine exactly what a formation anywhere in the body is and diagnose it, a sample must be taken by biopsy and examined in pathology. Many people undergo biopsies for various conditions, with results appearing as pathology reports. Patients often become confused and anxious on receiving them. We explain common pathology findings that are not cancer, although some carry cancer risk: hypertrophy, hyperplasia, atrophy, metaplasia and dysplasia.

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Cells adapt to environmental changes. Adaptations may occur normally (breast and uterine growth during pregnancy due to hormones) or pathologically. Pathological adaptations respond to stress by changing cell structure and function to avoid injury—solutions the body finds for difficult situations. Several forms exist:

What is hypertrophy?

Cell and organ size increases, often responding to greater workload, initiated by growth factors produced through mechanical stress or other stimuli, in tissues whose cells cannot divide. These are larger cells with increased structural components, not new cells. It can be physiological or pathological. Uterine growth in pregnancy and increased muscle mass in athletes are physiological examples; heart enlargement in hypertension is pathological.

What is hyperplasia?

In response to hormones and other growth factors, cell numbers increasein tissues with dividing cells or abundant stem cells. Physiological hyperplasia includes remaining liver cells proliferating to restore normal weight after partial removal. Pathological hyperplasia follows excessive hormone or growth factor stimulation. In some viral infections, growth factors drive hyperplasia; papillomaviruses cause warts, for example. Growth factors may be encoded by viral or infected host-cell genes.

These hyperplastic processes remain controlled; if initiating signals stop, hyperplasia disappears. Responsiveness to normal regulation distinguishes pathological hyperplasia from cancer, whose growth control is defective or ineffective. Nevertheless, pathological hyperplasia often provides fertile ground for cancer; uterine hyperplasia, for example, increases uterine cancer risk. Hyperplasia, hypertrophy may occur together, often responding to the same stimulus.

What is atrophy?

Due to reduced nutrients or disuse, cell and organ size decreases, associated with increased organelle breakdown and reduced production of building blocks. Atrophic cells may function less but are not dead. For example, prolonged immobilization of a broken arm for healing may cause muscle atrophy.

What is metaplasia?

It is a reversible replacement of one cell type by another better able to withstand adverse conditions. Usually arising from altered stem cell differentiation, it may reduce function or increase cancer susceptibility. A familiar example is respiratory epithelial cells (lining cells widespread in the body) changing into squamous epithelium in smokers. Although metaplastic cells gain survival advantages, important protective mechanisms such as mucus production and removal of harmful airborne particles are lost. Metaplasia is thus double-edged. Persistent initiating influences may predispose to cancer. Smoking is thought initially to cause squamous metaplasia, with cancers later developing in altered foci. 

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What is dysplasia?

Cells cease resembling each other and undergo structural change. Elements related to division (mitosis) increase greatly. When pronounced dysplasia involves the full thickness of an organ’s lining, it is called the precancerous stage carcinoma in situ . Although dysplasia often occurs adjacent to cancer foci, long-term smoker studies show epithelial dysplasia almost certainly precedes cancer. Dysplasia is not synonymous with cancer; mild-to-moderate dysplasia not involving the entire epithelial thickness returns completely to normal, particularly when its cause is removed (such as stopping smoking).

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