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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Pediatric Oncology

Decoding the Pathology Report and Risk Markers

At a Glance

A Wilms tumor pathology report guides treatment by detailing the tumor's histology (favorable or anaplastic) and genetic markers. Testing for markers like LOH 1p, 16q, and 1q gain helps pediatric oncologists assess the risk of relapse and adjust chemotherapy intensity.

After your child’s surgery, the removed tissue is sent to a pathologist—a doctor who studies cells under a microscope. Their findings are summarized in a pathology report. This document is the most important “map” for your child’s oncologist, as it determines the intensity of the treatment that follows [1][2].

The “Triphasic” Nature of Wilms Tumor

A classic Wilms tumor is described as triphasic, meaning it is made up of three different types of cells [3][4]:

  1. Blastemal cells: These are very immature, “busy” cells that look like the earliest stage of a developing kidney. If these cells remain alive (viable) after chemotherapy, it often suggests a more aggressive tumor [5][6].
  2. Stromal cells: These are connective tissue cells, like muscle or fat, that help support the tumor [4].
  3. Epithelial cells: These look like the more mature lining of the kidney’s filtering units [4].

The proportion of these cells—and how they reacted to any chemotherapy given before surgery—helps doctors categorize the tumor into risk groups (Low, Intermediate, or High) [5][7].

Favorable Histology vs. Anaplasia

The most critical distinction in the report is the histology (cell appearance):

  • Favorable Histology (FHWT): About 90% of Wilms tumors have “favorable” cells, which lack significant abnormalities and generally respond very well to treatment [8].
  • Anaplasia: This term describes cells with large, distorted nuclei that look very different from healthy cells. It is a marker of unfavorable histology because these cells are often more resistant to chemotherapy [8][9].
    • Focal Anaplasia: The abnormal cells are limited to one or two small spots. While technically an “unfavorable” finding, it is often treated as “intermediate risk” because the dangerous cells are contained and easier to manage than when they are widespread [10].
    • Diffuse Anaplasia: The abnormal cells are spread throughout the tumor. This is “high risk” and requires more intensive therapy [10][9].

Modern Risk Markers: Molecular Testing

In addition to looking at cells, scientists now look at the “fine print” of the tumor’s DNA. Certain genetic changes help predict if a tumor is more likely to return (relapse):

  • LOH 1p and 16q: This stands for Loss of Heterozygosity at chromosomes 1p and 16q. When a tumor loses both of these specific pieces of DNA, it has a higher chance of coming back. In these cases, doctors may “step up” or augment treatment to improve the chances of a cure [11][12].
  • 1q Gain: If the tumor has extra copies of chromosome 1q, it is also linked to an increased risk of relapse [13][14].

Completeness Checklist

When you review the report with your doctor, ensure the following six elements are present and clearly explained:

  • [ ] Histology Type: Is it Favorable (FHWT) or Anaplastic?
  • [ ] Anaplasia Pattern: If present, is it focal or diffuse? [9]
  • [ ] Molecular Markers: Were 1q gain and LOH 1p/16q tested, and what were the results? [11][13]
  • [ ] Surgical Margins: Are the edges of the removed tissue clear of cancer cells? [15]
  • [ ] Lymph Node Status: Were lymph nodes checked, and did they contain any tumor cells? (Note: Under the COG protocol, if the surgeon does not sample lymph nodes, the tumor is often automatically upgraded to Stage III) [16].
  • [ ] Viability (if post-chemo): What percentage of the tumor was “necrotic” (killed by chemo) versus “viable” (still alive)? [17]

Back to Home

Common questions in this guide

What is a triphasic Wilms tumor?
A classic Wilms tumor is 'triphasic,' meaning it contains three types of cells: blastemal, stromal, and epithelial. The proportion of these cells helps doctors determine how the tumor behaves and categorize it into risk groups for treatment.
What does favorable histology mean on my child's report?
Favorable histology means the tumor cells lack significant abnormalities and generally respond very well to standard treatment. Fortunately, about 90% of Wilms tumors have favorable histology.
What is the difference between focal and diffuse anaplasia?
Anaplasia refers to abnormal, distorted cells that are more resistant to chemotherapy. Focal anaplasia means these cells are limited to a small area, while diffuse anaplasia means they are spread throughout the tumor and require more intensive treatment.
Why does the pathology report include molecular testing for LOH 1p and 16q?
Molecular testing looks at the tumor's DNA for specific genetic changes that increase the risk of the cancer returning. If the tumor shows Loss of Heterozygosity (LOH) at chromosomes 1p and 16q, doctors may increase treatment intensity to improve the chances of a cure.
Why is it important to know if the tumor is necrotic or viable?
If your child received chemotherapy before surgery, the report will show how much of the tumor was killed (necrotic) versus how much survived (viable). A high percentage of viable blastemal cells often suggests a more aggressive tumor needing stronger treatment.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Is my child's tumor classified as 'Favorable Histology' (FHWT) or 'Anaplastic'?
  2. 2.If anaplasia was found, was it focal or diffuse?
  3. 3.What were the results of the molecular testing for '1q gain' and 'LOH at 1p and 16q'?
  4. 4.Which cell type (blastemal, stromal, or epithelial) was the most prominent in the tumor?
  5. 5.If my child had preoperative chemotherapy, what percentage of the tumor was 'necrotic' (dead) vs 'viable' (alive)?
  6. 6.Were the surgical margins and all sampled lymph nodes clear of tumor cells?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (17)
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    Wilms Tumor With Hepatic and Pulmonary Metastases in a Toddler: A Case Report.

    Elaitari K, Boujida N, Jabour S, et al.

    Cureus 2025; (17(8)):e91176 doi:10.7759/cureus.91176.

    PMID: 41018429
  2. 2

    Wilms Tumor (Nephroblastoma), Version 2.2021, NCCN Clinical Practice Guidelines in Oncology.

    Balis F, Green DM, Anderson C, et al.

    Journal of the National Comprehensive Cancer Network : JNCCN 2021; (19(8)):945-977.

    PMID: 34416707
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    Wilms' tumor in a 51-year-old patient: An extremely rare case and review of the literature.

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    Molecular and clinical oncology 2016; (4(6)):1013-1016 doi:10.3892/mco.2016.839.

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    A case report of infantile cystic nephroblastoma.

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    PMID: 30368245
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    Immunohistochemical analysis of cyclin A expression in Wilms tumor.

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    PeerJ 2019; (6()):e6212 doi:10.7717/peerj.6212.

    PMID: 30648000
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    Tumor Microenvironment and Immune Response Against Wilms Tumor: Evasion Mechanisms and Implications for Immunotherapeutic Approaches.

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    Cancers 2026; (18(6)) doi:10.3390/cancers18060908.

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    [Paediatric kidney tumours: Update on the challenges of nephroblastoma and other kidney tumours].

    L'Herminé-Coulomb A, Berrebi D

    Annales de pathologie 2026; (46(3)):195-206 doi:10.1016/j.annpat.2026.02.011.

    PMID: 41881740
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    Bromodomain 4 inhibition leads to MYCN downregulation in Wilms tumor.

    Woods AD, Berlow NE, Ortiz MV, et al.

    Pediatric blood & cancer 2022; (69(2)):e29401 doi:10.1002/pbc.29401.

    PMID: 34693628
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    Anaplasia in Wilms tumor: A critical review.

    Vujanić GM, Mifsud W

    Pediatric blood & cancer 2024; (71(7)):e31000 doi:10.1002/pbc.31000.

    PMID: 38605554
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    Characteristics and outcomes of preoperatively treated patients with anaplastic Wilms tumors registered in the UK SIOP-WT-2001 and IMPORT study cohorts (2002-2020).

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    Augmentation of Therapy for Combined Loss of Heterozygosity 1p and 16q in Favorable Histology Wilms Tumor: A Children's Oncology Group AREN0532 and AREN0533 Study Report.

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    Journal of clinical oncology : official journal of the American Society of Clinical Oncology 2019; (37(30)):2769-2777 doi:10.1200/JCO.18.01972.

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    Biomarkers for Wilms Tumor: A Systematic Review.

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    The Journal of urology 2016; (196(5)):1530-1535 doi:10.1016/j.juro.2016.05.100.

    PMID: 27259655
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    Gain of chromosome 1q and MYCN characterize unique subgroups of Asian Wilms tumor patients.

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    Cancer treatment and research communications 2026; (47()):101191 doi:10.1016/j.ctarc.2026.101191.

    PMID: 41905202
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    Copy Number Variations in Wilms Tumor: A Pilot Study From India.

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    Evaluation of the nephron-sparing surgery formula in Wilms tumors.

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    Outcome of Stage IV Completely Necrotic Wilms Tumour and Local Stage III Treated According to the SIOP 2001 Protocol.

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This page explains Wilms tumor pathology terminology for educational purposes. Your child's pediatric oncologist and pathologist are the best sources for interpreting your specific test results.

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