Pilomatricoma: Understanding Your Pathology Report

Section Editor: Allison Osmond MD FRCPC
September 13, 2026

A pilomatricoma is a noncancerous growth that develops from the cells at the base of a hair follicle, the structures in the skin that make hair. It is one of the commonest lumps removed from a child’s skin.

Your report may use a different spelling or an older name. Pilomatrixoma means the same thing, as does calcifying epithelioma of Malherbe, the name used when the growth was first described. All three refer to the same diagnosis.

This article is written for parents and caregivers. A pilomatricoma is not cancer, it does not become cancer, and once it is removed it rarely comes back. Most of what follows explains why it felt so hard and why the surgeon may not have known what it was beforehand. It also covers the one situation in which finding one leads to further questions.

What causes a pilomatricoma?

A hair follicle has a growth zone at its base called the matrix, where the cells that will become the hair shaft are made. A pilomatricoma forms when a group of those matrix cells keeps dividing instead of maturing into hair.

This happens because of a change in a gene called CTNNB1, which is found in most pilomatricomas. That gene makes a protein called beta-catenin, which normally helps control when hair follicle cells grow and when they stop. When the gene is changed, that control is lost.

The change happens by chance within the skin of the person who has it. It is not inherited, is not caused by anything a parent did, and is not related to injury, hygiene, or hair care.

How common is a pilomatricoma, and where does it occur?

Pilomatricoma is one of the most frequent skin growths removed in childhood. Roughly half of all cases occur in people under 20, with a peak in the first decade of life and a second, smaller peak in older adults.

More than half develop in the head and neck, most often on the cheek, in front of or below the ear, or on the eyelid and eyebrow. The arms and shoulders are the next commonest sites. Most are a single growth measuring 1 to 3 centimeters.

What does a pilomatricoma feel and look like?

The features families and clinicians notice are quite characteristic once you know them.

Hard. Often described as stone-like or bony. This is because the growth contains calcium deposits, and it is the single most useful clue.
Fixed to the skin but movable over the tissue beneath. The lump moves with the skin rather than sliding under it.
A bluish or reddish tinge to the skin above it. Sometimes with fine visible blood vessels.
Angular edges when the skin is stretched. Pulling the skin taut over the lump reveals flat facets and sharp corners rather than a smooth dome. Clinicians call this the tent sign.
Painless and slow-growing. Most are noticed by chance rather than because they cause trouble.

Occasionally a pilomatricoma becomes inflamed, breaks through the skin, and discharges chalky material. That is alarming to see but does not change the diagnosis or its noncancerous nature.

Why it is often mistaken for something else

This is worth knowing, because many families are told one thing before surgery and something different afterward.

In a review of 137 children with a pilomatricoma, the correct diagnosis had been made before surgery in only 38 percent. The rest were thought to be something else, most often an epidermoid cyst, another kind of cyst, a swollen lymph node, or occasionally something more worrying.

A pilomatricoma can also take up the tracer used in PET scans, which can raise concern about cancer when the scan was done for another reason entirely. Your child may have been investigated for a possible serious diagnosis before the answer turned out to be a pilomatricoma. That sequence is common and does not mean anyone made an error.

How is the diagnosis made?

Doctors confirm the diagnosis by removing the growth and examining it under a microscope. Imaging can suggest it, particularly an ultrasound showing a hard lump with calcium in it, but it cannot confirm it.

A needle sample is sometimes taken first, and this is one situation where that approach can mislead. The cells of a pilomatricoma look unusual enough on a needle sample that they have been mistaken for cancer cells. A pathologist examining the entire removed growth sees the full picture and can diagnose it with confidence.

What the pathologist sees

A pilomatricoma has a microscopic appearance unlike anything else, and two cell types define it.

Basaloid cells. Small, dark, closely packed cells at the edge of the growth. These are the actively dividing cells, and they resemble the matrix cells at the base of a normal hair follicle.
Shadow cells. Also called ghost cells. These sit at the center and are the remains of basaloid cells that have tried to become hair. Each has a pale pink body with a space where its nucleus used to be, leaving an outline, or shadow, of the cell.

Between the two is a transition zone where one cell type is turning into the other. Calcium deposits are present in most, and some also contain bone. Multinucleated giant cells are usually present too, part of the body’s reaction to the keratin the growth produces.

Reports sometimes note that the growth is actively dividing or that mitotic figures are frequent. In a pilomatricoma, this is expected and is not a sign of cancer. It reflects the basaloid cells doing what hair matrix cells normally do.

Beta-catenin

Most reports do not need any additional testing, because the microscopic appearance is distinctive. If the appearance is unusual or the sample is small, a beta-catenin stain may be used.

Normally beta-catenin sits at the edges of cells. In a pilomatricoma, the changed gene causes it to collect inside the nucleus of the basaloid cells instead, and a stain shows it there; if your report mentions nuclear beta-catenin, that supports the diagnosis rather than indicating anything concerning.

When there is more than one

The great majority of children have a single pilomatricoma, and a single one has no wider meaning. Having two over the years is not unusual either.

Multiple pilomatricomas, particularly several at once or a steady succession of them, are a different matter. Several inherited conditions are associated with them, and in those conditions the skin growths sometimes appear before anything else is recognized.

Myotonic dystrophy. A muscle condition. The association is well described, and it can affect the child or a parent.
Gardner syndrome. A form of familial adenomatous polyposis, which causes bowel polyps and has important implications for the whole family.
Turner, Rubinstein-Taybi, and Sotos syndromes. Each has been reported in association with multiple pilomatricomas.

If your child has had several, it is reasonable to ask whether any assessment for an underlying condition is appropriate. You can read more in our article What is a hereditary cancer syndrome? For a child with one growth and nothing else of note, no such assessment is needed.

Can a pilomatricoma be cancer?

There is a cancerous counterpart, called pilomatrix carcinoma, but it is exceedingly rare and occurs almost entirely in adults, with an average age around 52. It is essentially not a consideration in a child.

An ordinary pilomatricoma does not turn into it. The two are separate diagnoses from the outset. A pathologist distinguishes them by looking for invasion into surrounding tissue and markedly abnormal cells, neither of which is present in a pilomatricoma.

What happens after it is removed?

Complete surgical excision is the treatment, and for almost all children it is the only treatment needed. The growth does not respond to creams or medication and does not disappear on its own.

Your report will usually describe the margins, the edges of tissue cut by the surgeon. When the growth is completely removed, it rarely comes back. If a small amount is left behind, it can regrow, which is the usual reason a pilomatricoma returns.

No follow-up appointments, imaging, or blood tests are needed for a single completely removed pilomatricoma. It is reasonable to mention any new hard lump to your doctor, both because a second one can occur and because several over time raise the question described above.

Questions to ask your doctor

Does the report confirm a pilomatricoma, and does it use any other name for it?
Was the growth completely removed, and were the margins clear?
If it wasn’t completely removed, does anything else need to be done?
Is there any chance this is something other than a pilomatricoma?
Was a beta-catenin stain done, and what did it show?
The report mentions dividing cells. Does that mean anything concerning?
Has my child had one of these before, and does the number matter?
Should my child be assessed for an underlying condition?
What should I do if another hard lump appears?
Will there be a scar, and does the site need any particular care?
Does my child need any follow-up appointments?
Is there anything my child should avoid while the site heals?