Hepatoblastoma

Slide 1 · Hepatoblastoma

Developmental pathology • molecular mechanisms • clinicopathologic interpretation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Recognize the defining clinical and pathologic features of hepatoblastoma.

Link Wnt/β-catenin activation and inherited risk syndromes to tumor development.

Distinguish epithelial, mixed epithelial–mesenchymal, and important small-cell patterns.

Interpret diagnosis, PRETEXT extent, response markers, and treatment in context.

Slide 3 · A primary childhood liver malignancy

Hepatoblastoma is the characteristic hepatocellular malignancy of early childhood.

It resembles immature stages of hepatic differentiation rather than adult liver tissue.

Hepatocellular carcinoma is a distinct entity and must not be conflated with it.

Primary pediatric liver tumor

Hepatoblastoma

Other tumors ≠ hepatoblastoma

A distinct malignant epithelial entity

Slide 4 · Age is a major diagnostic clue

Most children present before 3 years of age; Occurrence beyond this age is uncommon.

Tumors with overlapping hepatoblastoma and hepatocellular carcinoma morphology may occur in older children.

“hepatocellular neoplasm, not otherwise specified” for this overlapping category.

Conceptual age distribution

Infancy–3 y

Older children: Uncommon

No numerical curve is implied

Slide 5 · Incidence has increased

An increasing incidence of hepatoblastoma.

NCI PDQ reports U.S. Incidence rising from 0.8 to 2.3 cases per million children aged ≤19 years across the periods shown.

The cause of the increase is not established; Associations should not be interpreted as proven causation.

U.S. Incidence, children ≤19 y

0.8

2.3

1975–83

2020

Cases per 1 million (NCI PDQ)

Slide 6 · Hepatic developmental identity

The tumor contains cells with fetal or embryonal hepatocytic morphology.

Growth patterns evoke liver development but do not recreate normal liver architecture.

The developmental appearance underlies the names of the principal epithelial patterns.

Original morphology schematic — not a photomicrograph

Hepatic-like plates

Immature epithelial tubules

Simplified architecture only; No stain or scale is represented

Slide 7 · The clinical–pathologic model

An early-childhood hepatic mass suggests a developmental liver tumor.

Histology determines the pattern of differentiation and alerts to divergent components.

Anatomic extent, dissemination, and response influence management beyond morphology alone.

Early-childhood hepatic mass

Histology / molecular context

Extent + metastatic work-up

Multidisciplinary treatment

Slide 8 · Wnt/β-catenin signaling is central

Activation of Wnt signaling is characteristic of hepatoblastoma.

Nuclear accumulation of β-catenin is an important pathway consequence.

Expression of Wnt-regulated genes, including glutamine synthetase, is increased in nearly all cases.

Wnt pathway activation

β-catenin stabilization

Nuclear β-catenin

Wnt target expression

Slide 9 · What β-catenin redistribution means

Membranous β-catenin participates in cell adhesion; Nuclear accumulation indicates transcriptional signaling.

Nuclear β-catenin is mechanistically relevant, but interpretation requires morphologic context.

A pathway marker alone does not substitute for a diagnosis.

Regulated β-catenin

Nuclear redistribution

Transcriptional effects

Morphologic context

Slide 10 · The CTNNB1 molecular route

NCI genomics PDQ identifies activating variants/deletions involving CTNNB1 exon 3 as a major mechanism.

Such alterations can stabilize β-catenin and favor nuclear signaling.

Molecular findings complement, rather than replace, histopathologic interpretation.

CTNNB1 exon 3 alteration

Reduced β-catenin turnover

Nuclear signaling

Developmental gene program

Slide 11 · APC: A second route to Wnt activation

APC normally restrains β-catenin signaling.

Germline APC loss-of-function causes familial adenomatous polyposis (FAP).

FAP is a recognized predisposition syndrome for hepatoblastoma.

APC loss of function

Impaired pathway restraint

β-catenin signaling

Hepatoblastoma predisposition

Slide 12 · Hereditary predisposition is not universal

Most presentations are not explained by an identified inherited syndrome.

Risk associations warrant family and congenital-feature assessment.

A tumor risk factor is neither diagnostic proof nor evidence of inevitability.

APC / FAP

Beckwith–Wiedemann

Other predispositions

Slide 13 · Beckwith–Wiedemann syndrome

Beckwith–Wiedemann syndrome is associated with congenital overgrowth and hepatoblastoma risk.

The underlying abnormality concerns imprinting at chromosome 11p15.

The precise alteration can vary; Syndromic risk is not uniform across molecular subgroups.

11p15 imprinting disruption

Abnormal fetal growth regulation

Predisposition ≠ diagnosis

Slide 14 · Imprinting and growth regulation

Altered 11p15 imprinting can drive insulin-like growth factor 2 (IGF2) overexpression.

Associated loss of CDKN1C expression removes a cell-cycle restraint.

CDKN1C encodes the cyclin-dependent kinase inhibitor p57.

11p15 imprinting abnormality

IGF2 ↑

CDKN1C / p57 ↓

Growth signaling ↑

Cell-cycle inhibition ↓

Slide 15 · Two mechanisms, one developmental tumor

Wnt signaling promotes transcriptional programs associated with growth and differentiation.

Altered imprinting can increase growth-factor activity and impair cell-cycle regulation.

These are associated routes; A single linear pathway must not be assumed for every tumor.

Wnt/β-catenin

Growth / imprinting

Developmental tumor biology

Slide 16 · Other recognized risk contexts

NCI lists prematurity with very low birth weight among the epidemiologic associations.

Other listed conditions include isolated hemihyperplasia and additional overgrowth syndromes.

Association strength and appropriate surveillance depend on the specific patient context.

Very low birth weight

Isolated hemihyperplasia

Selected congenital syndromes

Slide 17 · Prematurity and causation

Very low birth weight correlates with increased hepatoblastoma risk.

Better survival of very premature infants may contribute to observed incidence trends.

A specific causal factor from neonatal intensive care has not been demonstrated.

Observed association

Biologic explanation uncertain

No proved ICU exposure cause

Slide 18 · Screening in predisposed children

Selected predisposition syndromes prompt pediatric tumor-surveillance consideration.

Abdominal ultrasonography and serum AFP appear in published syndrome-specific strategies.

Age, genotype, regional guideline, and specialist assessment determine screening decisions.

Genotype + clinical assessment

Ultrasound ± AFP in protocols

Specialist surveillance plan

Slide 19 · The two broad Robbins morphologic groups

Epithelial hepatoblastoma contains fetal and/or embryonal hepatocyte-like cells.

Mixed epithelial and mesenchymal tumors add divergent stromal differentiation.

The groups describe observed tissue components, not clinical stage.

Epithelial

Mixed epithelial + mesenchymal

Slide 20 · Epithelial hepatoblastoma

Small polygonal fetal cells and smaller embryonal cells may coexist.

Cellular architecture includes trabeculae, acini, tubules, or papillary formations.

The relationship to normal hepatic developmental stages is approximate.

Original morphology schematic — not a photomicrograph

Hepatic-like plates

Immature epithelial tubules

Simplified architecture only; No stain or scale is represented

Slide 21 · Fetal-pattern differentiation

A more mature epithelial component resembles fetal hepatocytes.

Relatively orderly hepatocytic plates may be present.

The term “fetal” is a histologic descriptor, not an indication that the lesion is benign.

Original morphology schematic — not a photomicrograph

Orderly fetal-like plates

Contrast: Embryonal forms

Simplified architecture only; No stain or scale is represented

Slide 22 · Embryonal-pattern differentiation

Embryonal cells are smaller and less differentiated than fetal cells.

Tubular and acinar structures may be prominent in immature epithelial areas.

Mixed fetal–embryonal morphology is common in clinically encountered tumors.

Original morphology schematic — not a photomicrograph

Smaller embryonal cells

Tubular organization

Simplified architecture only; No stain or scale is represented

Slide 23 · Trabeculae, acini, tubules, papillae

Each term denotes an architectural configuration of the neoplastic epithelium.

A single neoplasm may display several patterns in different areas.

Architecture must be assessed with nuclear and cytoplasmic features.

Original morphology schematic — not a photomicrograph

Trabeculae

Acini

Tubules

Papillae

Simplified architecture only; No stain or scale is represented

Slide 24 · Mixed epithelial–mesenchymal tumors

An epithelial hepatoblastoma component coexists with mesenchymal differentiation.

The mesenchymal element may be primitive or demonstrate tissue formation.

A small biopsy can underrepresent heterogeneity across the mass.

Hepatocytic epithelium

Primitive stroma

Heterologous tissues

Slide 25 · Mesenchymal differentiation

Robbins specifically describes primitive mesenchyme, osteoid, cartilage, and striated muscle.

The mesenchymal component broadens the histologic appearance.

Unexpected heterologous tissue should trigger careful tumor-wide sampling.

Primitive mesenchyme

Osteoid

Cartilage

Striated muscle

Slide 26 · Why histologic sampling matters

A focal component may be absent from limited biopsy material.

Sampling should account for regions of distinct gross texture and microscopic pattern.

Post-treatment specimens may show therapy-related changes that complicate subtype assignment.

Conceptual pathology model

Slide 27 · Modern subtype language adds resolution

Contemporary pediatric tumor classification recognizes clinically relevant epithelial patterns.

Important categories include well-differentiated fetal, mixed fetal/embryonal, and small-cell patterns.

Robbins’ two broad groups remain useful for introductory morphology.

Well-differentiated fetal

Mixed fetal / embryonal

Small-cell component

Slide 28 · Well-differentiated fetal histology

This pattern is associated with favorable outcomes in specific, completely resected cohorts.

Use the complete pathologic criteria and treatment context, not “fetal” appearance alone.

Do not generalize outcomes from selected resected cases to all hepatoblastomas.

Original morphology schematic — not a photomicrograph

Orderly fetal-like plates

Contrast: Embryonal forms

Simplified architecture only; No stain or scale is represented

Slide 29 · Mixed fetal and embryonal histology

Both epithelial differentiation states may coexist in one tumor.

The relative distribution may vary between sampled blocks.

A designation based on limited tissue should communicate uncertainty when appropriate.

Original morphology schematic — not a photomicrograph

Fetal component

Embryonal component

Simplified architecture only; No stain or scale is represented

Slide 30 · Small-cell components need scrutiny

Primitive small cells can resemble other pediatric small-round-cell neoplasms.

Current diagnostic evaluation particularly considers malignant rhabdoid tumor of the liver.

Morphology alone can be insufficient for this distinction.

Small undifferentiated cells

Histologic overlap

SMARCB1 + expert review

Avoid premature assignment

Slide 31 · SMARCB1 in the small-cell differential

Loss of SMARCB1 (INI1) staining is characteristic of malignant rhabdoid tumor.

Small-cell undifferentiated hepatoblastoma may retain SMARCB1 expression.

NCI recommends testing small-cell undifferentiated cases to inform classification and care.

Primitive small-cell tumor

SMARCB1 IHC

Retained → assess hepatoblastoma

Lost → consider rhabdoid tumor

Slide 32 · Avoid the “primitive = rhabdoid” shortcut

Not every small-cell area is a rhabdoid tumor.

Integrate cytomorphology, other epithelial components, and SMARCB1 immunostaining.

Ambiguous lesions warrant expert pediatric pathology review.

Immature morphology

Does not prove rhabdoid tumor

Check SMARCB1 / context

Seek expert interpretation

Slide 33 · How to describe a specimen

Specify epithelial patterns and any mesenchymal differentiation actually identified.

Identify unusual primitive, small-cell, or rhabdoid-appearing areas.

Record sampling limitations and prior chemotherapy when present.

Components documented

Small-cell areas noted

Therapy status specified

Sampling limits described

Slide 34 · The microscopic architecture is heterogeneous

Cell size, maturation, and tissue pattern may differ within the same mass.

Classification should not rely on a single picturesque focus.

The combined assessment is more defensible than an isolated marker result.

Original morphology schematic — not a photomicrograph

Fetal-like

Embryonal-like

Additional epithelium

Mesenchymal stroma

Simplified architecture only; No stain or scale is represented

Slide 35 · β-catenin: Interpret the compartment

Nuclear localization supports Wnt-pathway activation.

A stain’s localization pattern is more informative than an unlabeled “positive”.

Staining must be assessed against internal controls and histologic context.

Immunostain localization

Nuclear β-catenin

Correlate with architecture

Integrate other findings

Slide 36 · Glutamine synthetase as pathway readout

Increased glutamine synthetase expression as a Wnt target-gene consequence.

The finding supports pathway activity but is not exclusive proof of hepatoblastoma.

Integrate with age, morphology, other markers, and imaging.

Wnt signaling

Nuclear β-catenin

Glutamine synthetase ↑

Interpret within tumor context

Slide 37 · Molecular findings and their roles

CTNNB1 or APC alterations explain a common oncogenic signaling theme.

Additional molecular signatures are under study for biological stratification.

Do not describe an exploratory molecular association as an established clinical decision rule.

Conceptual pathology model

Slide 38 · Diagnosis is a synthesis

Clinical age and liver-mass presentation establish the diagnostic setting.

Imaging defines anatomy; Pathology establishes tumor identity when tissue is obtained.

Tumor markers and selected ancillary tests contribute separate information.

Clinical context

Tumor imaging

Histology / markers

Risk-adapted planning

Slide 39 · Presentation: A growing abdomen

Abdominal swelling or mass is a typical initial finding.

The child may otherwise appear well at presentation.

A largely asymptomatic presentation does not imply localized disease.

Abdominal swelling

Hepatic mass identified

Define extent and symptoms

Tumor-specific evaluation

Slide 40 · Liver-related symptoms may occur

Jaundice and pruritus are reported in a subset of patients.

These findings reflect disturbance of hepatic or biliary function, not a unique tumor signature.

Their absence cannot exclude hepatoblastoma.

Slide 41 · The lung is an important metastatic site

Approximately 20% have lung metastases by diagnosis.

Distant disease changes risk assessment and management.

Thoracic evaluation therefore matters in the initial staging work-up.

Slide 42 · Serum AFP is useful but not specific

Alpha-fetoprotein (AFP) is elevated in most children with hepatoblastoma.

It is neither pathognomonic nor uniformly elevated.

Benign conditions, other tumors, and normal infancy can affect interpretation.

AFP often elevated

Not cancer-specific

Not universally elevated

Slide 43 · Why infant AFP requires care

Serum AFP is physiologically high in neonates and declines with age.

Use an age-adjusted reference range rather than an adult cutoff.

An isolated AFP result never determines tumor histology or stage.

High neonatal baseline

Physiologic decline

Age-adjusted comparison

Slide 44 · AFP can monitor response

Serial values often parallel disease burden during treatment.

Failure of a meaningful decline raises concern for inadequate response.

Interpret kinetics together with imaging, treatment timing, and age.

Baseline

Serial AFP + imaging

Assess response together

Slide 45 · Imaging answers an anatomic question

Ultrasound can identify a hepatic mass and guide the initial work-up.

Cross-sectional imaging delineates tumor distribution and major vascular relations.

Imaging also informs whether complete resection appears feasible.

Ultrasound: Identify mass

CT / MRI: Define anatomy

Chest evaluation: Lung spread

Slide 46 · PRETEXT: Pretreatment hepatic extent

PRETEXT is an imaging-based stratification of tumor extent before therapy.

It uses four functional liver sections derived from segmental liver anatomy.

The system assesses uninvolved contiguous sections and additional risk annotations.

Four-section conceptual representation

A

B

C

D

Schematic sections—not anatomical boundaries

Slide 47 · PRETEXT I through IV

Group I: Three adjoining hepatic sections remain tumor free.

Group II: Two adjoining sections remain tumor free.

Group III: One hepatic section remains tumor free.

Group IV: No hepatic section remains tumor free.

Four-section conceptual representation

A

B

C

D

Schematic sections—not anatomical boundaries

Slide 48 · PRETEXT vascular annotations

V denotes major hepatic venous/inferior vena cava involvement.

P denotes portal venous involvement.

These features may constrain safe resection even when tumor volume appears limited.

V: Hepatic veins / IVC

P: Right + left portal veins

Major vascular relationships

Slide 49 · Other PRETEXT annotations

E: Contiguous extrahepatic extension; F: Multifocal disease.

R: Tumor rupture; M: Distant metastases, commonly involving lungs.

These are separate descriptors and must not be inferred from PRETEXT I–IV alone.

E: Extrahepatic extension

F: Multifocal • R: Rupture

M: Distant metastasis

Slide 50 · PRETEXT and POSTTEXT are distinct

PRETEXT records anatomic extent before treatment.

POSTTEXT reassesses extent following chemotherapy.

Both should use documented imaging findings rather than imagined tumor shrinkage.

PRETEXT: Before therapy

POSTTEXT: After therapy

Slide 51 · Risk stratification is multidimensional

Important variables include PRETEXT category, metastatic disease, and serum AFP.

Vascular involvement, tumor rupture, age, and histology provide further context.

Contemporary risk group definitions are protocol-dependent.

PRETEXT extent

AFP + metastasis

Annotations / histology

Risk-adapted protocol

Slide 52 · Low AFP can be an adverse feature

Unexpectedly low AFP at diagnosis is uncommon in hepatoblastoma.

NCI links low AFP with adverse outcomes and certain primitive tumors.

The exact threshold and interpretation depend on age and study protocol.

Unexpected low AFP

Reassess morphology

Check protocol risk criteria

Slide 53 · Surgery and chemotherapy are complementary

Surgical resection plus chemotherapy as key treatments.

Complete macroscopic tumor removal is central to cure.

Treatment sequencing depends on resectability and disease extent.

Pathology + extent

Chemotherapy when indicated

Complete surgery

Long-term monitoring

Slide 54 · Primary resection is selective

Some limited, safely resectable tumors undergo upfront surgery.

Other patients require diagnostic biopsy and systemic therapy before resection.

Decision-making belongs to an experienced pediatric liver tumor team.

Anatomic resectability

Expert surgical assessment

Resect now or biopsy + therapy

Reassess if neoadjuvant

Slide 55 · Neoadjuvant chemotherapy may convert resectability

Chemotherapy can reduce mass and improve resectability.

Imaging and AFP response contribute complementary reassessment.

Pathologic classification of post-treatment tissue must account for therapy-related change.

Pretreatment imaging

Systemic treatment

POSTTEXT + AFP

Surgical decision

Slide 56 · Transplantation in selected unresectable disease

Liver transplantation is an option for tumors that remain unresectable after chemotherapy.

Major-vessel involvement and distribution affect operative planning.

Advanced cases warrant early specialist evaluation rather than late salvage referral.

Liver-confined unresectable disease

Expert transplant planning

Chemotherapy strategy

Definitive liver replacement

Slide 57 · Outcome figures require context

Robbins gives approximately 80% overall 5-year survival.

NCI PDQ separately reports approximately 70% in its overall summary.

These estimates come from different summaries; Do not interpret the difference as a direct trend.

Illustrative source-summary comparison

Robbins 11e: ≈ 80%

NCI PDQ: ≈ 70%

Different summaries, not a time series

Slide 58 · Clinicopathologic scenario: A toddler

A 20-month-old develops progressive painless abdominal swelling.

Cross-sectional imaging shows a solid hepatic mass; The patient is otherwise well.

What diagnoses, markers, and staging questions should be prioritized?

Diagnostic decision

Clinical mass in toddler

Which tests define identity and extent?

Slide 59 · Interpretation of the toddler scenario

Hepatoblastoma is a high-priority diagnosis in the age-appropriate setting.

AFP assessment requires age-aware interpretation; Imaging defines PRETEXT and annotations.

Histologic sampling or upfront resection follows a specialist resectability assessment.

Age-appropriate suspicion

Age-adjusted AFP

PRETEXT + metastatic work-up

Expert resectability assessment

Slide 60 · Clinicopathologic scenario: Primitive cells

A liver biopsy contains an extensive undifferentiated small-cell population.

No convincing fetal-pattern epithelium appears in the initial cores.

Which specific ancillary test is particularly consequential?

Diagnostic decision

Small-cell liver biopsy

Which entity requires exclusion?

Slide 61 · Interpretation of the primitive-cell case

Assess SMARCB1/INI1 nuclear expression with appropriate internal controls.

Loss raises strong concern for malignant rhabdoid tumor of the liver.

Seek expert review and additional sampling as clinically appropriate.

Conceptual pathology model

Slide 62 · Integrated diagnostic checkpoints

Identify the clinical setting and embryonal/fetal hepatic morphology.

Recognize divergent mesenchymal tissue and investigate primitive small-cell areas.

Use Wnt markers as supporting evidence, not standalone proof.

Communicate tumor extent and treatment-related interpretive limitations.

Clinical presentation

Epithelial ± stromal pattern

Molecular support

Clinical staging

Slide 63 · Key references

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. Elsevier; 2026. Chapter 18, p 790.

National Cancer Institute. Childhood Liver Cancer Treatment (PDQ®), Health Professional Version.

National Cancer Institute. Childhood Cancer Genomics (PDQ®): Hepatoblastoma.

International Pediatric Liver Tumors Consensus Classification, summarized in NCI PDQ.

Primary textbook + NCI PDQ

Slide-specific citations in speaker notes