Retinoblastoma

Slide 1 · Retinoblastoma

Molecular pathogenesis • Histomorphology • Clinicopathologic risk

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain heritable and nonheritable RB1 inactivation using the two-hit model.

Recognize defining gross and microscopic patterns of retinoblastoma.

Relate optic nerve, choroidal and extraocular spread to prognosis.

Connect pathology with early detection, treatment and genetic surveillance.

Slide 3 · Retinoblastoma: The essential definition

Malignant retinal neoplasm arising in early childhood.

Most common primary intraocular malignancy of childhood.

Linked chiefly to biallelic loss of RB1 tumor-suppressor function.

A paradigm of hereditary cancer susceptibility and somatic tumor evolution.

Slide 4 · The retina is the anatomic site of origin

Vitreous

Neurosensory retina

Retinal pigment epithelium

Choroid

Sclera

Tumor growth

Original schematic — not a histologic specimen

Retinoblastoma develops within the retina and can enlarge into the vitreous space or extend into adjacent ocular tissues.

Slide 5 · Why this neoplasm is distinctive

A developing retina creates a time-limited population of susceptible precursor cells.

One germline pathogenic allele can predispose every retinal precursor to a second hit.

Multiple independent retinal tumors may form in predisposed children.

Early recognition can preserve life, ocular structures and useful vision.

Slide 6 · Opening clinical case: An abnormal red reflex

A young child is brought for assessment after a parent notices a white pupil in several flash photographs. No family history of eye cancer is known.

DISCUSS

What serious intraocular diagnosis must be excluded urgently?

Why does a negative family history not settle hereditary risk?

Slide 7 · Leukocoria is a clinical warning sign

A white pupillary reflex can reflect a retinal mass or other ocular pathology.

It warrants prompt dilated examination by an ophthalmologist.

Retinoblastoma is a critical diagnosis, not the only cause of leukocoria.

Delayed diagnosis can allow ocular and extraocular tumor progression.

Slide 8 · Other presenting features

Strabismus can signal impaired fixation from a retinal lesion.

Reduced vision may be difficult to detect in a preverbal child.

Advanced intraocular tumors may cause pain, redness or secondary glaucoma.

Symptoms alone cannot establish the diagnosis or determine heritable status.

Slide 9 · A clinically oriented diagnostic sequence

Suspicious red reflex / strabismus

Dilated fundus examination

Ocular imaging when indicated

Genetic risk assessment

Retinoblastoma is generally diagnosed clinically; Diagnostic intraocular biopsy is avoided because of seeding risk.

Slide 10 · What ocular examination and imaging contribute

Ophthalmic assessment

Indirect ophthalmoscopy identifies retinal tumor sites and foci.

Examination under anesthesia may be needed in young children.

Ultrasonography can identify intraocular mass and calcification.

Imaging and risk

MRI assesses optic nerve, orbital and intracranial extension.

Imaging complements the ocular examination rather than replacing it.

Avoid unnecessary ionizing radiation in heritable retinoblastoma.

Slide 11 · Retinoblastoma is primarily a genetic-pathogenesis model

RB1 is a tumor-suppressor gene at chromosome 13q14.

Loss of both functional RB1 alleles removes an important proliferative brake.

The initiating event may be constitutional or entirely somatic.

A minority of tumors follow an RB1-intact, MYCN-amplified pathway.

Slide 12 · Knudson’s two-hit principle

First RB1 allele inactivated

Second RB1 allele inactivated

RB checkpoint function lost

Retinal precursor expands

Both hits occur in the same tumor precursor; Germline predisposition changes where the first hit resides.

Slide 13 · Heritable retinoblastoma: Constitutional first hit

Constitutional RB1 variant

All retinal cells carry one altered allele

A retinal cell sustains a second hit

Tumor clone develops

Slide 14 · Nonheritable retinoblastoma: Two somatic hits

Retinal cell initially has two functional copies

One somatic RB1 hit

Independent second hit in that lineage

Tumor clone develops

Slide 15 · Heritable versus nonheritable disease

Feature

Heritable RB1-associated

Nonheritable RB1-associated

First hit

Germline / constitutional

Somatic in a retinal cell

Second hit

Somatic loss of remaining allele

Second somatic loss

Typical laterality

Often bilateral or multifocal

Usually unilateral and unifocal

Family implication

Relatives may be at risk

Usually no inherited predisposition

Slide 16 · Germline mutation is not synonymous with family history

Heritable retinoblastoma can arise from a de novo constitutional RB1 variant.

Affected children may have no relatives with retinoblastoma.

Bilateral or multifocal tumors strongly support constitutional susceptibility.

Unilateral disease does not exclude constitutional or mosaic RB1 alteration.

Slide 17 · Dominant predisposition, recessive cellular phenotype

Organism-level inheritance

A pathogenic constitutional RB1 variant confers inherited cancer susceptibility.

The predisposition can be transmitted as an autosomal dominant trait.

Each retinal precursor begins one step closer to transformation.

Cell-level oncogenesis

A single RB1 loss-of-function allele does not itself produce a tumor.

The neoplastic phenotype generally requires inactivation of both alleles.

This is tumor suppression behaving recessively at the cellular level.

Slide 18 · Why a single RB1 hit is insufficient

An intact RB1 allele can still produce functional retinoblastoma protein.

The remaining checkpoint function restrains inappropriate G1-to-S entry.

A subsequent event must disable the retained functional allele.

The two-hit concept illustrates selection of biallelic tumor-suppressor loss.

Slide 19 · Normal RB protein restrains S-phase entry

Hypophosphorylated RB binds E2F

E2F-dependent transcription is restrained

G1/S transition is controlled

RB is a central checkpoint integrator; Its status reflects mitogenic and antiproliferative signals.

Slide 20 · Cyclin–CDK complexes release the RB brake

Growth-factor signaling

Cyclin D–CDK4/6 and related CDKs active

RB hyperphosphorylated

E2F programs drive S-phase entry

Slide 21 · Functional RB inhibition versus RB1 gene loss

Genetic inactivation

Loss of both RB1 alleles removes the functional suppressor protein.

In a retinal precursor this can initiate retinoblastoma.

RB1 is the canonical tumor-suppressor prototype.

Pathway-level inactivation

Other cancers may impair RB activity through cyclin or CDK dysregulation.

RB1 may be structurally intact but functionally inactivated.

The distinction matters when interpreting molecular mechanisms.

Slide 22 · What is the susceptible cell?

Retinoblastoma emerges from a developing retinal lineage.

Modern genetic studies implicate a cone photoreceptor precursor context.

The disease illustrates that molecular lesions interact with cellular lineage.

RB1 expression elsewhere does not mean equivalent tumor susceptibility everywhere.

Slide 23 · An important RB1-negative molecular subset

A small minority of retinoblastomas lack identifiable RB1 inactivation.

High-level MYCN amplification can drive an RB1-intact tumor.

The older name NMYC refers to MYCN.

This route should not be inferred solely from morphology.

Slide 24 · Why hereditary tumors are frequently bilateral

Heritable predisposition

All developing retinal precursors start with an altered RB1 allele.

Separate second hits can create independent tumor foci.

Bilateral or multifocal presentation can therefore occur.

Sporadic disease

Two independent somatic events must meet in one retinal lineage.

This is a rarer combination than one additional hit.

The usual presentation is a single unilateral tumor.

Slide 25 · Pathologic morphology does not reveal germline status

Tumors from heritable and nonheritable cases have the same basic morphology.

Rosettes, necrosis and calcification do not identify the inherited first hit.

Laterality, family history and molecular testing establish genetic risk.

Histology answers local tumor questions, not constitutional genotype alone.

Slide 26 · Case: Two independent retinal masses

A toddler has separate tumors in both eyes. Ophthalmoscopy shows multiple retinal foci; The parents report no affected relatives.

DISCUSS

Which RB1 susceptibility pattern is most likely?

Should germline testing still be considered?

Slide 27 · Macroscopic pathology: Intraretinal tumor expansion

Retinoblastoma begins as a retinal neoplasm.

The enlarging tumor may replace retinal tissue and form an intraocular mass.

Tumor extension toward the vitreous and other structures influences local stage.

The true macroscopic extent must be determined by direct pathologic examination.

Slide 28 · Tumor growth changes the normal retinal compartment

Vitreous

Neurosensory retina

Retinal pigment epithelium

Choroid

Sclera

Tumor growth

Original schematic — not a histologic specimen

The lesion displaces normal retinal architecture; The schematic depicts anatomy, not clinical fundus imaging.

Slide 29 · Undifferentiated tumor: Primitive neuroblastic cells

Dense collections of small, round tumor cells are characteristic.

Nuclei are deeply basophilic and hyperchromatic.

Tumor cells may appear relatively uniform in poorly differentiated areas.

Microscopic heterogeneity includes differentiated foci in some tumors.

Slide 30 · Flexner–Wintersteiner rosettes: True lumina

True central

Lumen

Tumor cells encircle a genuine lumen.

Shows photoreceptor differentiation.

Not required for a diagnosis.

Editable schematic — not microscopy

Slide 31 · Interpreting a true Flexner–Wintersteiner rosette

Tumor cells are radially arranged around a central lumen.

The architecture implies retinal / photoreceptor differentiation.

Rosettes can be present among less differentiated cells.

Their absence does not by itself exclude retinoblastoma.

Slide 32 · Homer Wright pseudorosette: Fibrillary center

Fibrillary core

Cell ring surrounds neuropil-like fibers.

A pseudorosette, not a true lumen.

Less specific than Flexner–Wintersteiner rosettes.

Editable schematic — not microscopy

Slide 33 · Histologic rosettes and differentiated elements

Structure

Central feature

Interpretation

Flexner–Wintersteiner

True lumen

Retinal differentiation

Homer Wright

Fibrillary neuropil-like material

Neuroblastic differentiation

Fleurette

Flower-like cells; No true lumen

Greater photoreceptor differentiation

Slide 34 · Fleurettes indicate photoreceptor differentiation

Fleurettes form flower-like arrangements of differentiated tumor cells.

They represent a maturation pattern within retinal tumor tissue.

Fleurettes and Flexner–Wintersteiner rosettes reflect related differentiation.

Differentiation alone is not a reliable prognostic classifier.

Slide 35 · Viable tumor cuffs and ischemic necrosis

Vessel

Calcific deposits

Viable perivascular cells

Hypoxic / necrotic territory

Mechanistic schematic — distance from blood supply is explanatory, not a measured scale

Slide 36 · Why necrosis develops away from vessels

Rapidly growing retinal tumor tissue depends on its vascular supply.

Viable tumor remains closest to patent vessels.

Relatively avascular regions develop ischemic cell death.

The viable-to-necrotic gradient explains a frequent histologic pattern.

Slide 37 · Dystrophic calcification in retinoblastoma

Calcific foci commonly accompany necrotic tumor tissue.

This is dystrophic calcification, not evidence of systemic hypercalcemia.

Calcification is diagnostically helpful on histology and ocular imaging.

Necrosis and mineralization should not be mistaken for a tumor grade.

Slide 38 · Histologic recognition: Positive and negative evidence

Supportive findings

Malignant small round cells arising in the retina.

True rosettes or fleurettes may show differentiation.

Perivascular viability and dystrophic calcification support the pattern.

Interpretive limits

Rosettes are not invariably present.

Degree of histologic differentiation does not by itself predict prognosis.

The hereditary and sporadic forms are morphologically indistinguishable.

Slide 39 · Retinocytoma / retinoma: A related lesion

Retinoma (retinocytoma) is a relatively differentiated retinal proliferation.

It is considered a possible precursor of retinoblastoma.

An affected eye may contain retinoblastoma while the fellow eye has retinoma.

This combination is particularly pertinent to heritable disease.

Slide 40 · Retinoma versus retinoblastoma

Retinoma / retinocytoma

A relatively differentiated retinal lesion with precursor potential.

May be detected during hereditary retinoblastoma assessment.

Still warrants directed ophthalmic surveillance.

Retinoblastoma

Malignant proliferating retinal tumor.

Includes primitive cells, necrosis and sometimes differentiated structures.

Needs assessment of local invasion and overall clinical extent.

Slide 41 · Histologic differentiation is not the main prognostic axis

The textbook explicitly notes poor association between differentiation and prognosis.

A well-formed rosette should not reassure against invasive spread.

Extent of local invasion is more clinically consequential.

Reporting must prioritize optic nerve, uveal and extraocular involvement.

Slide 42 · Choroidal invasion connects microscopic spread to risk

Sclera

Choroid

Retina

Tumor

Choroidal infiltration

Pathology: Depth and extent of invasion matter more than microscopic differentiation

Slide 43 · Massive choroidal invasion: A reporting priority

Choroidal invasion is an adverse feature when extensive.

A consensus framework uses a maximum invasive focus dimension of at least 3 mm for “massive” invasion.

The local pathology protocol must define orientation and measurement.

Prognostic thresholds and treatment consequences remain protocol-dependent.

Slide 44 · Optic nerve invasion must be anatomically localized

Prelaminar

Lamina cribrosa

Retrolaminar

Resection margin

Determine anatomic level and margin status; Postlaminar spread is a high-risk feature

Slide 45 · Postlaminar optic nerve invasion is high risk

Invasion beyond the lamina cribrosa implies an advanced neural route.

Microscopic level is more informative than simply recording invasion present.

Tumor at an optic nerve transection margin is particularly consequential.

Pathology reports must document the deepest invasion level.

Slide 46 · Adverse features of retinoblastoma

Feature

Why clinically important

Extraocular extension

Tumor has escaped the confines of the globe

Postlaminar optic nerve invasion

Access to an important route for extraocular spread

Massive choroidal invasion

Substantial uveal invasion associated with metastasis risk

Optic nerve cut end involved

Concern for residual tumor along nerve pathway

Slide 47 · There is no single universal high-risk feature set

Definitions of high-risk pathology differ across retinoblastoma centers.

A global survey found consensus for postlaminar nerve invasion, a positive nerve transection and extrascleral extension.

Other criteria, including choroidal and anterior segment findings, varied by practice.

Interpret a histologic feature in the context of the center’s documented protocol.

Slide 48 · Anatomic routes of spread

Intraocular retinal neoplasm

Optic nerve / choroid / sclera involvement

Extraocular or systemic dissemination

Brain and bone marrow dissemination; Lung involvement is relatively uncommon.

Slide 49 · Metastatic behavior is anatomically patterned

Spread to the brain is a major concern with advanced retinoblastoma.

Bone marrow is another characteristic systemic site.

Lung dissemination is less characteristic than in many other solid tumors.

Risk rises with extraocular extension and invasive histologic findings.

Slide 50 · Trilateral retinoblastoma

Heritable retinoblastoma can be associated with an intracranial primitive neuroblastic malignancy.

The classic association is pineal-region disease.

This constellation is termed trilateral retinoblastoma.

A particularly poor outcome for this association.

Slide 51 · A second cancer risk beyond the eye

Constitutional RB1 loss predisposes to later primary cancers.

Osteosarcoma and soft-tissue sarcomas are characteristic examples.

The risk is not limited to recurrent ocular disease.

This motivates individualized survivorship counseling and exposure awareness.

Slide 52 · Three treatment goals must be ordered correctly

First: Protect survival

Eradicate a potentially fatal malignancy.

Control intraocular or extraocular disease.

Assess histologic and clinical metastatic risk.

Next: Preserve eye and vision

Preserve the affected globe where oncologically safe.

Maintain or recover useful vision where feasible.

Protect the child from avoidable long-term morbidity.

Slide 53 · Chemoreduction plus focal tumor consolidation

Selected intraocular tumor

Chemotherapy reduces burden

Laser / cryotherapy targets residual tumor

Repeat ophthalmic surveillance

Slide 54 · Selective intra-arterial ophthalmic chemotherapy

Medication can be delivered selectively through the ophthalmic artery.

This approach concentrates treatment at the eye in eligible cases.

Its suitability depends on laterality, tumor distribution and specialist evaluation.

Local control still requires longitudinal ocular assessment.

Slide 55 · When enucleation is clinically important

A severely involved eye may be unsafe or impossible to salvage.

Enucleation can remove the tumor while allowing complete pathologic staging.

Optic nerve length, cut margin and uveal invasion deserve meticulous evaluation.

The decision balances systemic safety against ocular preservation.

Slide 56 · Enucleation pathology: Necessary observations

Document the tumor distribution, size and associated retinal changes.

Sample tumor in relation to choroid, sclera and optic nerve head.

State the deepest optic nerve infiltration and optic nerve margin status.

Describe any extraocular tissue extension and recognized adverse findings.

Slide 57 · Treatment choice is not determined by rosette abundance

What histology tells us

Well-differentiated histology does not guarantee a low-risk tumor.

High-risk invasion findings may change postoperative management.

Need to distinguish histologic structure from disease extent.

What clinical staging adds

Tumor size, laterality, foci and eye condition influence local treatment.

Optic nerve or orbital spread changes systemic evaluation.

Vision potential affects globe-sparing decisions when oncologically safe.

Slide 58 · Genetic evaluation guides family-level prevention

Identify whether a constitutional RB1 pathogenic variant is present.

Offer variant-specific assessment of at-risk relatives when feasible.

Germline negative blood testing does not always exclude low-level mosaicism.

Family counseling must distinguish a heritable predisposition from tumor-only mutations.

Slide 59 · Genetic testing: A practical interpretation pathway

Retinoblastoma diagnosis

Constitutional RB1 assessment

Tumor molecular workup when available

Risk-based surveillance for child and relatives

Gene testing is complementary to urgent clinical treatment, not a reason to postpone it.

Slide 60 · Surveillance in germline RB1 carriers

The developing retina is examined repeatedly during early childhood.

Some examinations require anesthesia until reliable cooperation is possible.

Frequency and duration are individualized by genetic and clinical risk.

Specialist schedules are more reliable than a one-size-fits-all interval.

Slide 61 · An eye saved is not necessarily a child discharged

Local control does not abolish the constitutional cancer predisposition.

The fellow eye can develop additional lesions when RB1 is heritable.

Long-term follow-up includes functional vision and subsequent cancer awareness.

Surveillance is matched to genotype, disease status and treatment history.

Slide 62 · Clinicopathologic case: Optic nerve extension

An enucleated globe contains retinoblastoma with tumor extending beyond the lamina cribrosa into the optic nerve; The cut margin is negative.

DISCUSS

Which histologic feature is adverse?

What additional anatomic sites and report elements should be reviewed?

Slide 63 · Morphology case: Differentiated islands

Microscopy of a retinal tumor shows sheets of hyperchromatic small round cells, numerous necrotic foci, and several true rosettes surrounding lumina.

DISCUSS

Which differentiated structure is illustrated by the rosettes?

Can rosette frequency establish a favorable prognosis?

Slide 64 · Genetic counseling case: A unilateral tumor

A child has a single unilateral retinal tumor and no affected family members. An RB1 pathogenic variant is detected in peripheral blood.

DISCUSS

Does unilateral disease exclude a constitutional predisposition?

What does this finding imply for follow-up and relatives?

Slide 65 · High-yield reasoning: Phenotype to inference

Observation

What it supports

What it does not prove

Bilateral multifocal tumors

Constitutional predisposition

A known positive family history

True retinal rosettes

Photoreceptor differentiation

Favorable clinical outcome

Necrosis with calcification

Typical tumor architecture

A specific genetic subclass

Postlaminar nerve invasion

High-risk invasive spread

Established distant metastasis

Slide 66 · Retinoblastoma: Five integrative conclusions

Retinal neoplasia generally follows biallelic RB1 tumor-suppressor loss.

A germline first hit predisposes to bilateral, multifocal and second primary tumors.

Small blue cells, true rosettes, perivascular necrosis and calcification define the morphologic framework.

Differentiation is not a stand-alone prognostic marker.

Optic nerve, choroid and extraocular spread drive adverse pathologic risk.

Slide 67 · Further reading

Robbins, Cotran & Kumar: Pathologic Basis of Disease. 11th edition. Chapters 7 and 29.

GeneReviews: Retinoblastoma (NCBI Bookshelf NBK1452).

International Retinoblastoma Staging Working Group: pathology consensus (2009).

Retinoblastoma high-risk pathology: multicenter practice survey (2021).