Section Editor: Allison Osmond MD FRCPC
June 14, 2026
Pathologists use the term atypical melanocytic proliferation to describe a skin growth composed of melanocytes (the cells that produce pigment) that does not appear completely normal under the microscope. The growth shows some unusual or atypical features, but not all of the features needed to confidently call it benign (noncancerous) or malignant (cancerous). It is best thought of as a description of uncertainty rather than a final diagnosis. This article explains what the term means, what the findings in your pathology report describe, and how those findings guide the next steps in your care.
Is an atypical melanocytic proliferation a type of cancer?
An atypical melanocytic proliferation is not the same as a diagnosis of cancer. At the same time, it does not completely rule out the possibility that the growth could behave like a melanoma (a type of skin cancer). The term reflects genuine uncertainty about whether the growth is benign or malignant, and pathologists use it when the features under the microscope make a definite diagnosis difficult. It is a way of saying that the growth needs careful evaluation and follow-up to ensure nothing is missed.
What does an atypical melanocytic proliferation look like?
On the skin’s surface, an atypical melanocytic proliferation may resemble other nevi (moles) or pigmented spots. Features that may draw attention include:
- Uneven color — A spot with shades of brown, black, or even red.
- Irregular borders — Edges that are uneven or an unusual shape.
- Larger size — A spot larger than most moles, sometimes more than about 6 millimeters (the size of a pencil eraser).
- Change over time — A spot that has become darker, larger, or more irregular.
Because these features can overlap with both harmless and concerning growths, any unusual or changing spot should be examined by a doctor, who may remove a sample for microscopic examination.
How is the diagnosis made?
The term is applied after a skin growth is biopsied or removed and examined under the microscope by a pathologist. Under the microscope, melanocytes may appear larger, darker, or more irregular than normal; they may grow in an unexpected or uneven pattern; and they may extend into the deeper layers of the skin. Often, the growth shows a mix of features seen in benign moles and melanoma, which makes it impossible to confidently place it in either group.
When the features are borderline, pathologists frequently ask one or more colleagues, often a dermatopathologist (a pathologist who specializes in skin diseases), for a second opinion. The clinical context, such as the location of the growth, the patient’s age and history, and how the spot looked and behaved before removal, also helps guide its classification. Additional tests may be used to help in difficult cases, including immunohistochemistry (special stains such as PRAME and p16) and molecular tests (such as FISH or other genetic tests) that look for changes more often found in melanoma.
What happens after this diagnosis?
Because the diagnosis is uncertain, the care team usually takes a cautious approach to protect the patient and avoid unnecessary procedures. The findings in the report, along with the size and location of the growth and the patient’s history, guide what is considered, which may include:
- Complete removal — The growth is often completely removed with a margin of normal skin around it. This removes atypical cells and allows the pathologist to examine the entire growth, providing the most reliable assessment of whether it is benign or malignant.
- Expert review — The case may be sent to one or more specialized pathologists for additional opinions.
- Close follow-up — Regular skin examinations are usually recommended to watch for any new or returning growths.
If a fuller evaluation shows the growth is benign, no further treatment beyond routine skin checks is usually needed. If it is reclassified as melanoma, treatment follows the melanoma pathway. Working closely with your doctor is the best way to decide on the right next steps for your situation.
Questions to ask your doctor
- What atypical features were seen, and how concerning are they?
- Was the whole growth removed, or only part of it?
- Do I need a wider excision to remove the rest with a clear margin?
- Was my case reviewed by a second pathologist or a dermatopathologist?
- Were any special tests (immunohistochemistry, FISH, or molecular testing) done, and what did they show?
- Is there a chance this could be melanoma?
- How will I be monitored, and how often?
- What changes should prompt me to call you?
- What can I do to protect my skin from sun damage?
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