Dysplasia: Definition

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Dysplasia is a word pathologists use to describe cells that look abnormal and disorganized under the microscope but have not turned into cancer. In most parts of the body, dysplasia is a precancerous change, which means the cells carry a higher-than-normal risk of developing into cancer over time if they are left untreated. The abnormal cells are still confined to the surface layer or their original location; they have not invaded deeper tissues or spread to other parts of the body.

Dysplasia is almost always reported together with a grade (low grade or high grade) and the part of the body where it was found, for example low-grade dysplasia of the colon or high-grade dysplasia of the cervix. This article explains what dysplasia means on a pathology report, how it is found and graded, and what the different results mean for follow-up. (A few unrelated conditions, such as fibrous dysplasia of bone, also use the word “dysplasia” but are not precancerous; these are explained near the end.)

Does dysplasia mean cancer?

No. Dysplasia is not cancer. It describes abnormal cells that have the potential to develop into cancer over time but have not yet gained the ability to invade nearby tissues or spread to other parts of the body. For this reason, dysplasia is best understood as a warning sign, one that can often be monitored or treated to prevent cancer from developing.

How do pathologists identify dysplasia?

Dysplasia is identified when a pathologist examines a tissue sample under the microscope. The sample is usually collected during a biopsy, for example during a colonoscopy, a colposcopy of the cervix, or a skin biopsy, depending on where the abnormal area is located. Under the microscope, the pathologist looks for cells that have lost their normal, orderly arrangement. Features that suggest dysplasia include enlarged and darkly staining nuclei (the part of the cell that holds its DNA), cells that vary in size and shape, an increased number of dividing cells, and a loss of the normal way cells mature as they move toward the surface. In dysplasia, these changes are limited to the surface layer of cells (the epithelium) and have not broken through into the tissue below. This is the key feature that separates dysplasia from invasive cancer.

How do pathologists grade dysplasia?

When dysplasia is found, the pathologist assigns a grade based on how abnormal the cells look and how much of the tissue is involved. The grade helps predict how likely the dysplasia is to progress to cancer and guides decisions about whether to monitor the area or treat it. Most parts of the body now use a two-tier system:

Low-grade dysplasia (mild) — The cells are only mildly abnormal and still resemble normal cells in many ways. The risk of progression to cancer is relatively low, and close monitoring is often the chosen approach.
High-grade dysplasia (moderate to severe) — The cells are markedly abnormal and closely resemble cancer cells, although they have not invaded. This grade carries a higher risk of progressing to cancer and more often leads to treatment, such as removal of the abnormal area.

Some older reports, and a few specific sites, still use a three-tier system (mild, moderate, and severe). In that system, moderate and severe dysplasia together correspond to high-grade dysplasia. When high-grade dysplasia involves the full thickness of the surface layer, it may also be called carcinoma in situ.

How often does dysplasia turn into cancer?

The likelihood that dysplasia will become cancer varies widely depending on its location, its grade, and its underlying cause. In general, high-grade dysplasia carries a greater risk of progressing to cancer than low-grade dysplasia. For example, high-grade dysplasia of the cervix (also called a high-grade squamous intraepithelial lesion or HSIL) is more likely to progress to cervical cancer than low-grade dysplasia of the cervix (also called a low-grade squamous intraepithelial lesion or LSIL). Even so, not all dysplasia progresses; some cases stay stable or resolve completely.

Can dysplasia go away on its own?

Sometimes. Low-grade dysplasia can occasionally resolve on its own, particularly when the underlying cause is removed or controlled. For example, low-grade dysplasia of the cervix caused by a human papillomavirus (HPV) infection may clear once the immune system clears the virus. High-grade dysplasia is much less likely to go away on its own and usually needs treatment.

What causes dysplasia?

Dysplasia develops when cells build up genetic changes that disrupt the normal control of cell growth, causing the cells to look and behave abnormally. These changes can accumulate for several reasons, including:

Chronic inflammation, such as from long-term irritation or an inflammatory disease.
Prolonged hormonal stimulation, such as long-term exposure to estrogen.
Viral infections, most notably HPV.
Exposure to harmful substances, such as tobacco smoke or ultraviolet (UV) radiation from the sun.

Over time, these genetic changes disrupt normal cell growth, causing cells to look and behave abnormally.

Is dysplasia always a precancerous change?

In most parts of the body, dysplasia is a precancerous change. However, the word “dysplasia” is also used for a few unrelated conditions that are not precancerous. Fibrous dysplasia, for example, is a bone condition in which normal bone is replaced by abnormal fibrous tissue; it can weaken or deform the bone but does not turn into cancer. Skeletal dysplasias are a group of inherited conditions that affect how bones and cartilage develop. These conditions share the name “dysplasia” because they involve abnormal growth or development, but they do not carry the cancer risk of the epithelial dysplasia seen on most pathology reports.

What is the difference between dysplasia and metaplasia?

Dysplasia and metaplasia both describe abnormal cell changes, but they differ in their appearance under the microscope, their causes, and their relationship to cancer:

Dysplasia — Abnormal growth in which cells look disorganized and abnormal in structure. Dysplasia is precancerous and can progress to cancer.
Metaplasia — A change in which one type of normal cell is replaced by another type of normal cell, usually in response to chronic irritation or inflammation. Metaplasia is not itself precancerous, but it can create an environment in which dysplasia later develops.

Understanding this distinction helps explain why some findings are watched closely while others are not.

Questions to ask your doctor

What grade of dysplasia was found, low grade or high grade?
Where in my body was the dysplasia found?
What is the chance that this dysplasia could turn into cancer over time?
Do I need treatment now, or can this be monitored?
If monitoring is recommended, how often will I need follow-up tests or biopsies?
What is the likely cause of my dysplasia, and can anything be done to reduce it?
If treatment is needed, what are my options?
Will I need repeat testing to make sure the dysplasia has not come back?