Clear Cell Carcinoma

Slide 1 · Ovarian Clear Cell Carcinoma

Pathogenesis • morphology • diagnosis • clinicopathologic significance

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Recognize clear cell carcinoma as a distinct ovarian epithelial histotype.

Relate endometriosis and molecular alterations to pathogenesis.

Identify the major gross and microscopic architectural patterns.

Select and interpret a focused immunohistochemical panel.

Explain how stage modifies prognosis and diagnostic priorities.

Slide 3 · Five principal ovarian carcinoma histotypes

High-grade serous

Frequently linked to fallopian tube precursor lesions.

Low-grade serous

A different molecular and clinical pathway from high-grade serous.

Endometrioid

Endometrial-type glands; May be associated with endometriosis.

Clear cell

Distinct WHO histotype; Characteristically complex architecture and clear/hobnail cells.

Mucinous

Intestinal/gastric-type mucinous differentiation; Exclude metastasis.

Slide 4 · Defining ovarian clear cell carcinoma

A malignant epithelial neoplasm with characteristic architecture and cytology.

Large epithelial cells often have abundant optically clear cytoplasm.

Recognition requires integration of architecture, cytology, and context.

Clear cytoplasm alone is neither necessary nor sufficient for diagnosis.

Slide 5 · Textbook terminology versus current classification

Robbins: descriptive relationship

WHO 2020: diagnostic classification

Notes overlap with ovarian endometrioid carcinoma.

Lists clear cell carcinoma as a separate principal histotype.

Shared mutations help explain biological relationships.

Histotype assignment remains morphologically informed.

Do not interpret “variant” as a current synonym.

Report the distinctive clear cell carcinoma diagnosis.

Slide 6 · A relatively uncommon ovarian carcinoma

Clear cell carcinoma as approximately 6% of malignant ovarian tumors.

It is substantially less frequent than serous carcinoma.

Benign and borderline clear cell tumors are exceedingly rare.

Relative rarity makes histotype-specific recognition important.

Slide 7 · Benign, borderline, and malignant clear cell lesions

Category

Meaning in this context

Benign

Exceedingly rare according to Robbins.

Borderline

Exceedingly rare; not a common pathway.

Clear cell carcinoma

The clinically important malignant epithelial category.

Slide 8 · Association with ovarian endometriosis

Endometriosis is a recognized setting for ovarian clear cell carcinoma.

A carcinoma may coexist with an endometriotic cyst.

Endometriosis-associated tumors share biological themes with endometrioid carcinoma.

An association is not proof that every tumor arose from endometriosis.

Slide 9 · Endometriosis-associated carcinogenesis

Ovarian endometriosis

Atypical epithelial change in a subset

Acquired oncogenic alterations

Clear cell carcinoma

A conceptual pathway in a subset of tumors; Not all endometriosis progresses to malignancy.

Slide 10 · Association, precursor evidence, and causation

Observation

Interpretive strength

Endometriosis near a carcinoma

Association; not automatically direct precursor evidence.

Contiguous atypical endometriosis

Supports a precursor–carcinoma relationship.

Shared somatic molecular alteration

Supports clonal relationship in the studied lesion.

Slide 11 · What molecular study adds

Sample carcinoma

Sample adjacent atypical endometriosis

Test corresponding alterations

Assess potential clonal continuity

Concordant alterations can strengthen, but not replace, morphologic assessment.

Slide 12 · Clear cell and endometrioid carcinomas

Feature

Clear cell carcinoma

Endometrioid carcinoma

Classification

Distinct ovarian histotype

Distinct ovarian histotype

Endometriosis association

Recognized

Recognized

Typical morphology

Clear/hobnail cells; varied architecture

Endometrial-type tubular glands

Molecular overlap

ARID1A, PIK3CA and others

ARID1A, PI3K-pathway and other changes

Slide 13 · Genes cited for clear cell carcinoma

ARID1A

Chromatin remodeling; Shared with endometrioid tumors.

PIK3CA

A component of PI3K signaling.

PTEN

Negative regulator of the PI3K signaling pathway.

KRAS

Oncogenic signaling alteration in a subset.

TP53

May be altered; Not the signature event seen in high-grade serous cancer.

Slide 14 · ARID1A: Chromatin-remodeling disruption

ARID1A encodes a component of the SWI/SNF chromatin-remodeling machinery.

ARID1A alterations occur in a substantial subset of ovarian clear cell carcinomas.

Atypical endometriosis can share ARID1A loss with adjacent carcinoma.

Loss of BAF250a expression is a surrogate for some ARID1A alterations, not a universal diagnostic criterion.

Slide 15 · PIK3CA: Oncogenic signaling

PIK3CA encodes the catalytic PI3K α subunit.

PIK3CA alterations are recurrent in ovarian clear cell carcinoma.

PI3K signaling promotes cellular growth and survival.

A molecular alteration does not replace histologic identification of the carcinoma subtype.

Slide 16 · PI3K pathway — simplified causal relation

PIK3CA activation or PTEN loss

Increased PI3K–AKT signaling

Enhanced survival / growth signaling

Clonal selection

General pathway interpretation; A teaching schematic, not a patient-specific validated assay.

Slide 17 · Why shared mutations do not imply identical tumor types

Molecular finding

Interpretation

ARID1A or PIK3CA alteration

May be seen in clear cell and endometrioid carcinoma.

Overlapping molecular pathways

Biological relationship, not morphological equivalence.

Histotype-specific appearance

Remains important for diagnosis and prognosis.

Slide 18 · TP53 requires careful interpretation

TP53 mutation is characteristic of high-grade serous carcinoma, not a universal feature of clear cell carcinoma.

TP53 among alterations reported in clear cell carcinoma.

WHO-informed reviews describe TP53 changes as less typical for clear cell carcinoma.

An abnormal p53 staining pattern should prompt review of morphology and differential diagnosis.

Slide 19 · Clear cell versus high-grade serous pathways

Feature

Clear cell carcinoma

High-grade serous carcinoma

Common setting

Endometriosis-associated in a subset

Tubal fimbrial/STIC pathway prominent

Characteristic genes

ARID1A; PIK3CA

TP53; homologous-recombination pathway

Typical p53 staining

Often wild-type pattern

Usually mutation-type pattern

WT1

Usually negative

Often diffuse positive

Slide 20 · Molecular alterations are supportive, not diagnostic alone

Morphology and histotype-directed immunohistochemistry drive classification.

ARID1A loss is not unique to ovarian clear cell carcinoma.

The genotype of a tumor must be interpreted with architecture and cytology.

Clinical site and potential metastasis can change the diagnostic question.

Slide 21 · Gross presentation: Solid and cystic components

Ovarian clear cell carcinoma may be predominantly solid or cystic.

Robbins explicitly describes both gross configurations.

A tumor can contain mixed solid and cystic regions.

Sampling must include visually different areas to characterize the lesion.

Slide 22 · Cystic tumors: Neoplastic epithelial lining

Conceptual schematic — not a histologic specimen

A cystic component is lined by neoplastic epithelial cells.

The cavity is a growth pattern, not proof of benign behavior.

Slide 23 · Solid tumors: Epithelial sheets

Conceptual schematic — not a histologic specimen

In a solid component, neoplastic epithelial cells may form dense sheets.

Solid growth alone is not specific for this histotype.

Slide 24 · Gross sampling priorities

Area

Why it matters

Solid focus

Can reveal epithelial cytology and additional architecture.

Cyst lining

Shows epithelial arrangement and any focal complexity.

Adjacent suspected endometriosis

Can document spatial association or transition.

Surface or capsular abnormality

Important for extent of disease; requires pathologic correlation.

Slide 25 · Gross appearance is not a substitute for histology

A solid–cystic ovarian mass is a pattern shared by several tumor types.

Gross configuration helps direct sampling.

The definitive histotype is established from microscopic findings.

Do not infer clear cell carcinoma from cyst color or contents alone.

Slide 26 · Three recurring microscopic architectures

Papillary, tubulocystic, and solid patterns are characteristic.

A single tumor may display more than one architecture.

Pattern recognition begins at low power.

Cytologic features and supportive staining refine the diagnosis.

Slide 27 · Tubulocystic architecture: Multiple lumina

Conceptual schematic — not a histologic specimen

Variably sized glands or cystic spaces are separated by tissue stroma.

Inspect the epithelial lining for clear and hobnail cells.

Slide 28 · Papillary architecture: Projecting fronds

Conceptual schematic — not a histologic specimen

Tumor-lined projections extend into spaces.

Papillary cores may contain prominent hyalinized material.

Slide 29 · Solid architecture: Confluent cell groups

Conceptual schematic — not a histologic specimen

Confluent epithelial sheets can coexist with papillary or tubulocystic regions.

The tumor is not defined by clear cytoplasm alone.

Slide 30 · Hobnail cells: Nucleus projects into a lumen

Conceptual schematic — not a histologic specimen

A hobnail cell has an eccentrically projecting nucleus toward the luminal surface.

This is a valuable pattern, not an obligatory finding.

Slide 31 · Clear cytoplasm: A cytologic clue

Large cells may show abundant optically clear cytoplasm.

This appearance helps explain the name “clear cell.”

Eosinophilic cytoplasm may also occur in clear cell carcinoma.

Other ovarian histotypes can contain clear cells.

Slide 32 · Nuclear features are part of the diagnosis

Evaluate nuclear enlargement, atypia, and prominent nucleoli.

The degree and distribution of atypia provide context.

Hobnail nuclear position is a separate feature from nuclear grade.

Atypia must be assessed in relation to the architecture.

Slide 33 · Hyalinized cores and extracellular material

Conceptual schematic — not a histologic specimen

Dense hyaline stromal material may expand papillary cores.

This supports, but does not establish, a diagnosis of clear cell carcinoma.

Slide 34 · Hyaline bodies: A supportive microscopic clue

Round eosinophilic hyaline bodies may be seen in ovarian clear cell carcinoma.

Hyaline material can occur within or around tumor structures.

Use the finding in combination with architecture and epithelial cytology.

The absence of hyaline bodies does not exclude the histotype.

Slide 35 · Architecture versus cytology

Architectural clue

Cytologic clue

Interpretation

Papillary growth

Clear or eosinophilic cells

One recognizable combination

Tubules / cysts

Hobnail nuclei

Another characteristic combination

Solid sheets

Large clear cells

Possible pattern; differential remains broad

Slide 36 · A crucial pitfall: Clear cells occur in other carcinomas

Do not diagnose ovarian clear cell carcinoma from a clear cytoplasmic phenotype alone.

High-grade serous carcinoma can show clear-cell change.

Endometrioid carcinoma can show clear-cell areas.

Use architecture, nuclei, immunophenotype, and full sampling.

Slide 37 · Microscopic examination at two scales

Low-power assessment

High-power assessment

Papillary, tubulocystic, or solid growth

Clear/eosinophilic cytoplasm

Relationship of patterns and stroma

Hobnail nuclear configuration

Associated endometriosis or adenofibromatous areas

Nuclear atypia, nucleoli, hyaline bodies

Slide 38 · The role of immunohistochemistry

Use stains to resolve a specific morphologic differential.

Panel selection follows the histologic question.

No single stain is perfectly sensitive and specific.

Interpret staining pattern, localization, and internal controls together.

Slide 39 · Core ovarian histotyping immunopanel

WT1

Often positive in high-grade serous carcinoma; Typically negative in clear cell.

P53

Mutation-type pattern suggests high-grade serous in the appropriate context.

Napsin A

Supports ovarian clear cell differentiation.

PR

Often more informative for endometrioid than clear cell carcinoma.

Slide 40 · Napsin A: A practical diagnostic adjunct

Napsin A is frequently expressed in ovarian clear cell carcinoma.

Cytoplasmic positivity supports clear cell differentiation.

Negative staining does not definitively exclude the tumor.

Napsin A is not exclusive to ovarian tumors; Clinical context matters.

Slide 41 · HNF1β: Supportive, not exclusive

HNF1β nuclear expression is commonly observed in ovarian clear cell carcinoma.

HNF1β is linked to the clear cell differentiation phenotype.

It can provide supportive evidence when morphology is suggestive.

Do not use HNF1β positivity alone to establish the primary site.

Slide 42 · PAX8: Establishes lineage, not necessarily origin

PAX8 is commonly expressed in Müllerian ovarian carcinoma.

PAX8 positivity supports an epithelial Müllerian-lineage differential.

Renal clear cell carcinoma can also express PAX8.

PAX8 alone cannot resolve ovarian versus renal primary origin.

Slide 43 · WT1 and p53 in the key serous differential

Marker

Clear cell carcinoma

High-grade serous carcinoma

WT1

Typically negative

Usually positive

p53

Often wild-type pattern

Commonly mutation-type pattern

Napsin A

Often positive

Usually negative

Slide 44 · Hormone receptor patterns

Marker

Typical ovarian clear cell

Typical endometrioid carcinoma

ER

Often negative

Often positive

PR

Often negative

Often positive

Interpretation

Negative receptors support when morphology matches

Receptor expression can favor endometrioid phenotype

Slide 45 · ARID1A immunostaining: Distinguish use cases

BAF250a loss can support an altered ARID1A pathway, but is not histotype-specific.

Loss requires retained internal positive controls.

Endometrioid ovarian tumors may also show ARID1A alterations.

ARID1A staining is not a substitute for morphology or the core histotyping panel.

Slide 46 · Focused histotyping workflow

Review H&E architecture

Form a defined differential

Choose WT1 / p53 / Napsin A / PR as indicated

Integrate IHC and morphology

Extend the panel according to site, history, and unusual findings.

Slide 47 · Clear cell versus endometrioid carcinoma

Question

Favors clear cell

Favors endometrioid

Architecture

Tubulocystic / papillary / solid

Endometrial-type tubular glands

Cells

Hobnail/clear or eosinophilic

Columnar glandular cells

Immunophenotype

Napsin A / HNF1β often positive

ER / PR often positive

Molecular overlap

ARID1A, PIK3CA possible

ARID1A, PI3K-pathway possible

Slide 48 · Clear cell versus high-grade serous carcinoma

Question

Favors clear cell

Favors high-grade serous

Architecture

Tubulocystic / hyalinized papillae

High-grade epithelial architecture

WT1

Usually negative

Usually positive

p53

Often wild-type

Usually mutation-type

Napsin A

Often expressed

Usually absent

Slide 49 · Metastatic renal clear cell carcinoma: Key pitfall

Feature

Ovarian clear cell

Metastatic renal clear cell

PAX8

May be positive

May be positive

CK7

Typically positive

Often negative/focal

CD10 / RCC marker

Usually not diffuse positive

Frequently supports renal origin

Deciding evidence

Full morphology + site context

Renal imaging/history + targeted panel

Slide 50 · A diagnosis is an integrated conclusion

Architecture + cytology + immunophenotype + clinical site.

Do not allow one aberrant stain to outweigh convincing morphology.

Consider concurrent endometrial disease and metastatic tumors when relevant.

State the ovarian histotype clearly when criteria are met.

Slide 51 · Clinical presentation: Symptoms are nonspecific

Ovarian carcinomas commonly present with lower abdominal pain or abdominal enlargement.

Pelvic pressure may produce urinary frequency or dysuria.

Gastrointestinal complaints can accompany pelvic masses.

Symptoms alone do not identify the histotype.

Slide 52 · From ovarian lesion to clinical manifestations

Ovarian mass growth

Distension / pressure effects

Capsular or surface extension

Peritoneal involvement ± ascites

Conceptual clinical progression; Timing and presentation vary between patients.

Slide 53 · Peritoneal dissemination matters

Ovarian carcinoma can seed peritoneal surfaces after extracapsular spread.

Ascites may contain exfoliated malignant cells.

Peritoneal disease changes the extent of disease and clinical course.

Clear cell histology does not eliminate the need for full staging assessment.

Slide 54 · Localized disease: A comparatively favorable outcome

Approximately 90% 5-year survival when clear cell carcinoma is confined to the ovaries.

This textbook estimate is conditional on localized disease.

It is not an individual patient prediction.

Do not generalize this survival figure to advanced-stage disease.

Slide 55 · Advanced disease: The prognosis changes markedly

Poor outcome with advanced-stage clear cell carcinoma.

Stage and spread are essential when interpreting survival.

WHO-informed reviews report lower sensitivity to standard platinum-based therapy.

Histotype and stage should both appear in clinicopathologic discussions.

Slide 56 · Why stage must accompany the histologic label

Localized disease

Advanced disease

Disease confined to ovarian site.

Extension beyond the ovary and/or metastatic deposits.

Robbins cites approximately 90% 5-year survival.

Robbins describes an unfavorable outcome.

Requires complete assessment of extent.

Requires comprehensive assessment of dissemination.

Slide 57 · CA-125: Monitoring versus screening

CA-125 is used in known ovarian carcinoma to monitor recurrence or progression.

It is not an adequately sensitive and specific population screening tool.

A single CA-125 value cannot assign ovarian histotype.

Interpret serial results with disease status and imaging when appropriate.

Slide 58 · Screening limitations and prevention

The absence of a sufficiently accurate general ovarian cancer screening assay.

Risk-based interventions are discussed for heritable BRCA-associated susceptibility.

Those interventions chiefly address broader ovarian cancer prevention, not a CCC-specific signature.

Avoid treating a negative screening test as exclusion of carcinoma.

Slide 59 · Clinical management is not defined by one stain

Treatment planning integrates histotype, extent, and patient context.

Clear cell carcinoma is treated as ovarian carcinoma.

Contemporary clinical guidance distinguishes epithelial ovarian histotypes.

Staining results support diagnosis; Treatment selection requires wider assessment.

Slide 60 · Diagnostic exercise: Morphology first

An ovarian mass shows tubulocystic and papillary epithelial growth, clear cytoplasm, and nuclei projecting into lumina.

Name the leading histotype.

State two supporting microscopic features.

Slide 61 · Exercise answer: Architectural and cellular pattern

Ovarian clear cell carcinoma is the leading consideration.

Tubulocystic / papillary architecture supports the diagnosis.

Hobnail cells and clear cytoplasm provide cytologic support.

An IHC panel is appropriate if the differential remains uncertain.

Slide 62 · Diagnostic exercise: An IHC differential

An ovarian carcinoma with clear-cell morphology is WT1-negative, shows a wild-type p53 pattern, and is Napsin A-positive.

Which histotype is supported?

Why should the result not be interpreted from Napsin A alone?

Slide 63 · Exercise answer: Interpret the panel together

The panel favors ovarian clear cell carcinoma when morphology is concordant.

WT1 negativity and nonaberrant p53 argue against typical HGSC.

Napsin A positivity supports clear cell differentiation.

The panel must be interpreted with histology and tumor site.

Slide 64 · Diagnostic exercise: Exclude metastasis

An ovarian clear-cell tumor is PAX8-positive in a patient with a prior renal malignancy.

Does PAX8 positivity prove an ovarian primary?

What additional diagnostic evidence is needed?

Slide 65 · Exercise answer: Assign the primary site carefully

PAX8 positivity alone does not distinguish ovarian from renal clear-cell carcinoma.

Review imaging and the known renal tumor.

Assess CK7, CD10, RCC marker, and other targeted stains.

Correlate architectural and cytologic features with the clinical history.

Slide 66 · Final synthesis: Diagnostic chain

Domain

Questions answered

Setting

Is the lesion ovarian? Is there endometriosis or a competing primary?

Morphology

Is there papillary, tubulocystic, or solid growth with characteristic cells?

IHC

Do WT1, p53, Napsin A and selected adjuncts fit the histotype?

Prognosis

Is the tumor confined to the ovaries or advanced?

Slide 67 · Selected references

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026; Chapter 22, pp. 924–929.

WHO Classification of Tumours Editorial Board. Female Genital Tumours. 5th ed. IARC; 2020.

ICCR. Ovary, Fallopian Tube and Primary Peritoneal Carcinoma — Histological tumour type.

De Leo A, et al. Diagnostics. 2021;11(4):697. doi:10.3390/diagnostics11040697.

Köbel M, et al. Cancers. 2022;14:416. doi:10.3390/cancers14020416.

ESMO Clinical Practice Guideline: epithelial ovarian cancer. Ann Oncol. 2023.