p53 in Endometrial Cancer

by Jason Wasserman MD PhD FRCPC
March 29, 2026

If your pathology or molecular report mentions p53, it refers to the result of a special stain or genetic test that looks at a protein — and the gene that makes it — that plays a central role in how cells control their own growth and repair their DNA. In endometrial cancer, testing for p53 is now a routine part of the molecular workup used to classify the cancer into one of four groups. These groups help your medical team understand how your cancer is likely to behave and guide treatment decisions. A p53 result that shows an abnormal pattern is one of the most important prognostic findings in endometrial cancer — but it is also one of the results that benefits most from careful explanation.

What the test looks for

The TP53 gene provides the instructions for making a protein called p53. In healthy cells, p53 acts as a tumour suppressor — when DNA becomes damaged, p53 helps to pause cell division long enough for repairs to be made, or triggers the cell to self-destruct if the damage is too severe. This makes p53 one of the most important safeguards against cancer development.

When the TP53 gene is mutated — meaning its instructions are altered — the p53 protein either stops working or accumulates abnormally inside the cell. Pathologists can detect this by performing a test called immunohistochemistry (IHC), which uses specially designed proteins called antibodies to stain p53 within tumour cells. A normal p53 result and an abnormal p53 result each produce a distinct staining pattern, which the pathologist interprets under the microscope.

In some cases, especially when results are borderline or a comprehensive molecular profile is needed, the TP53 gene may also be tested directly using next-generation sequencing (NGS). This technology reads the tumour’s genetic code to identify specific mutations.

Why is the test done

In endometrial cancer, p53 testing is one of four molecular tests used together to classify tumours into distinct groups. This system — known as the molecular classification of endometrial cancer — was developed after researchers discovered that certain molecular patterns predict how a cancer will behave far more accurately than tumour appearance under the microscope alone.

The four molecular groups are:

POLE-mutated (POLEmut). Tumours with mutations in the POLE gene, which controls DNA proofreading during cell division. Despite often looking aggressive under the microscope, these tumours have an excellent prognosis and may not need aggressive adjuvant treatment.
Mismatch repair-deficient (dMMR) / microsatellite instability-high (MSI-H). Tumours with defects in the mismatch repair machinery — a system that corrects errors in DNA. These tumours have intermediate outcomes and may benefit from immunotherapy. Patients with this finding should also be assessed for Lynch syndrome, a hereditary condition that raises the risk of several cancers.
p53 abnormal (p53abn). Tumours with an abnormal p53 result. This group is associated with the most aggressive behaviour and the poorest outcomes of the four groups. It corresponds closely to what pathologists previously called serous endometrial carcinoma or high-grade endometrioid carcinoma with p53 mutation, though the molecular category is now preferred.
No specific molecular profile (NSMP). Tumours that do not fall into any of the three groups above. This is the largest group and has intermediate outcomes that vary depending on other pathological features.

The p53 test helps determine whether a tumour belongs to the p53 abnormal group. This directly affects treatment decisions, including the intensity of adjuvant therapy — treatment given after surgery to reduce the risk of the cancer returning.

Importantly, the molecular groups are assessed in a specific order. If a tumour has a POLE mutation, it is classified as POLEmut regardless of its p53 result. A p53 abnormal result is only used to classify a tumour as p53abn after POLE mutation and mismatch repair deficiency have already been ruled out. This hierarchy matters because patients whose tumours are POLE-mutated have a very good prognosis even when p53 is also abnormal, and treating them based on the p53 result alone could lead to unnecessarily aggressive treatment.

p53 testing is recommended for essentially all newly diagnosed endometrial cancers, not just those that appear high-grade under the microscope. Tumour appearance alone can be misleading — some cancers that appear relatively low-grade can harbour a p53 mutation, and these patients benefit from early identification so that treatment can be appropriately intensified. In Canada, access to full molecular classification may vary by province and institution. If you have not been told whether your tumour has been molecularly classified, it is worth asking your oncologist or gynaecologic pathologist.

How the test is performed

The p53 IHC test is performed on a sample of tumour tissue, usually obtained during the initial surgery to remove the uterus (a hysterectomy) or during a biopsy performed before surgery. The tissue is preserved in a solution called formalin, embedded in wax, and sliced into very thin sections, which are then mounted on glass slides.

A laboratory technician then applies a liquid containing antibodies that bind specifically to the p53 protein. A chemical reaction causes the areas where p53 is present to become coloured under the microscope. The pathologist examines the slide and records both the pattern and the intensity of staining across the tumour cells.

If NGS is also performed — either as part of reflex molecular testing or because the IHC result is ambiguous — a separate portion of the tumour sample is used to extract DNA, which is then analysed using sequencing technology. NGS can identify the exact location and type of TP53 mutation, providing a more detailed picture than IHC alone.

How results are reported

The p53 IHC result is reported based on the staining pattern observed across the tumour cells. The pathologist does not simply record “positive” or “negative” — instead, they describe one of three staining patterns:

Wild-type pattern. A scattered, variable pattern of staining across different tumour cells — some cells stain, and some do not, and the intensity varies from cell to cell. This is the normal pattern and indicates that the p53 protein is functioning as expected. It does not mean there is no cancer; it means the cancer does not have a p53 mutation.
Overexpression pattern (diffuse strong positive). Approximately 80% of tumour cell nuclei stain strongly and uniformly for p53. This pattern indicates that the TP53 gene carries a missense mutation — a change in the genetic code that causes an abnormal p53 protein to accumulate inside cells. This is an abnormal result.
Complete absence pattern (null pattern). No staining at all in the tumour cells, even though nearby normal cells stain normally. This pattern indicates that the TP53 gene carries a mutation that prevents the p53 protein from being produced at all. This is also an abnormal result.

Either the overexpression pattern or the null pattern is classified as a p53 abnormal result. Both carry the same clinical significance.

When NGS results are available, the report will typically describe the specific mutation found — for example, a missense mutation at a particular position in the TP53 gene — and may classify it according to standard variant classification systems.

What the result means

Wild-type (normal) p53

A wild-type p53 result means the cancer does not have a detectable p53 mutation. The tumour will be classified into one of the other three molecular groups — POLEmut, dMMR, or NSMP — based on the remaining test results. A wild-type result does not determine prognosis on its own; the significance depends on what the other molecular tests show.

p53 abnormal

An abnormal p53 result — whether overexpression or null — indicates the tumour carries a mutation in the TP53 gene and is classified in the p53abn molecular group. This group is associated with a higher risk of the cancer spreading beyond the uterus, a higher risk of recurrence after treatment, and shorter survival compared to the other molecular groups.

In large studies of endometrial cancer, patients in the p53abn group have five-year progression-free survival rates of 40–50% for advanced-stage disease — significantly lower than the POLEmut group, where five-year progression-free survival exceeds 90%, and lower than the NSMP group as well. This difference is the primary reason why the p53abn classification triggers more intensive adjuvant treatment in most clinical guidelines.

It is important to understand that a p53 abnormal result describes the biology of the cancer — it is not a reflection of anything you did or did not do. TP53 mutations in endometrial cancer are acquired during tumour development and are not typically inherited from a parent or passed to children. This is different from germline TP53 mutations, which cause a rare hereditary condition called Li-Fraumeni syndrome. If you or your family have features that raise concern about hereditary cancer risk, your medical team can arrange a referral to a genetic counsellor.

Receiving a p53 abnormal result can feel overwhelming. What it means in your specific situation — including your stage, your overall health, and the other features of your cancer — is something your oncologist is best placed to discuss with you in detail.

What happens next

For most patients with a p53 abnormal endometrial cancer, the next step after surgery is a referral to a gynaecologic oncologist and a radiation oncologist to discuss adjuvant therapy. Current clinical guidelines support more intensive adjuvant treatment for p53abn tumours than for lower-risk molecular groups.

Adjuvant treatment for p53abn endometrial cancer typically involves a combination of chemotherapy and external beam radiation therapy to the pelvis. Vaginal brachytherapy — a form of internal radiation delivered to the top of the vaginal cuff — may also be included. The specific approach depends on the stage of the cancer at diagnosis and your overall health.

Immunotherapy is increasingly being studied in p53abn endometrial cancer, though its role remains evolving. Unlike dMMR tumours — where immune checkpoint inhibitors such as pembrolizumab have well-established benefit — p53abn tumours are often mismatch repair-proficient, meaning they tend to be less reliably responsive to immunotherapy alone. Clinical trials are ongoing, and your oncologist will be aware of options relevant to your situation.

If your cancer is diagnosed at an advanced stage or recurs after initial treatment, systemic therapy — including chemotherapy, targeted therapies, or enrolment in a clinical trial — will be discussed as part of your care plan.

Questions to ask your doctor

Has my tumour been fully molecularly classified — including testing for POLE mutations and mismatch repair status — in addition to p53?
What stage is my cancer, and how does the p53 abnormal result change my treatment plan?
What adjuvant treatment are you recommending, and what does the evidence show about its effectiveness in p53 abnormal endometrial cancer?
Is immunotherapy an option for me, either now or through a clinical trial?
Should I see a genetic counsellor to discuss whether my cancer or my family history could indicate a hereditary cause?
Are there any clinical trials I should consider?