Mucinous Tumors

Slide 1 · Mucinous tumors of the ovary

Morphologic spectrum · pathogenesis · diagnostic interpretation

Benign cystadenoma | borderline tumor | primary mucinous carcinoma

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Classify ovarian mucinous tumors by epithelial proliferation and stromal invasion.

Recognize the key gross and microscopic findings.

Explain the proposed roles of KRAS and possible cells of origin.

Distinguish primary ovarian disease from metastatic and peritoneal mucinous disease.

Slide 3 · Ovarian epithelial tumor classification

Epithelial differentiation

Mucinous phenotype

Behavioral category

Ovarian epithelial neoplasms are classified by both epithelial type and degree of proliferation/invasion.

Slide 4 · Two distinct axes describe a mucinous neoplasm

Axis

Question answered

Major categories

Differentiation

What epithelial type is present?

Mucinous, serous, endometrioid

Behavior

How does epithelium grow?

Benign, borderline, invasive

A mucinous phenotype does not alone establish a tumor’s malignant potential.

Slide 5 · Common as tumors; Uncommon as ovarian cancers

20–25%

Of all ovarian neoplasms are mucinous

≈3%

Of all ovarian cancers are primary mucinous carcinomas

Different denominators explain why these proportions should not be compared as if equivalent.

Slide 6 · Clinical age distribution

Mucinous tumors occur principally in middle adult life.

They are rare before puberty.

They are also uncommon after menopause.

Age is contextual information, not a microscopic criterion for malignancy.

Slide 7 · Most mucinous tumors are not invasive

≈80%

Benign

≈10%

Borderline

≈10%

Malignant

Approximate distribution in the ovarian tumor frequency table; Distinct from the fraction of all ovarian cancers.

Slide 8 · Three levels of mucinous tumor behavior

Benign

Simple mucinous lining

No invasive growth described

Borderline

Epithelial proliferation

No stromal invasion

Carcinoma

Invasive architecture

Expansile and/or destructive stromal invasion

Slide 9 · Type I ovarian carcinoma: Conceptual progression

Benign precursor

Borderline proliferation

Low-grade carcinoma

Mucinous carcinoma within the type I epithelial ovarian carcinoma pathway; Not every individual tumor must follow each step.

Slide 10 · KRAS is a recurring molecular alteration

KRAS is a proto-oncogene frequently mutated in ovarian mucinous tumors.

Mutations are reported in benign, borderline, and malignant categories.

This shared molecular feature is compatible with a lineage relationship among morphologically different areas.

It does not itself define stromal invasion.

Slide 11 · KRAS mutations span the morphologic spectrum

Benign cystadenoma

58%

Borderline tumor

75–86%

Mucinous carcinoma

85%

Frequencies reported, 11th ed.; Borderline values represent a range.

Slide 12 · Shared KRAS mutations: What a single tumor can show

Benign-appearing area

Borderline-appearing area

Malignant-appearing area

Identical KRAS mutations across distinct morphologic regions in a reported study support a possible early initiating alteration, not certainty about individual progression.

Slide 13 · Initiation is different from invasion

Molecular alteration

A KRAS mutation may occur early in tumor development.

Supports pathogenesis

Morphologic progression

Epithelial architecture and cytology can vary.

Requires histology

Invasive disease

Expansile or destructive patterns indicate carcinoma.

Requires evaluation of growth pattern

Slide 14 · Possible cells of origin remain diverse

Mucinous glands in teratomas

Brenner tumor–associated mucinous glands

Müllerian epithelium → mucinous differentiation

These are proposed origins, not three required sequential stages.

Slide 15 · Why histogenesis has been debated

Normal ovarian tissue lacks a straightforward resident counterpart of benign mucinous epithelium.

The diversity of gastric, intestinal, and occasional endocervical differentiation complicates simple origin models.

Associated teratomatous, Brenner, and müllerian epithelia supply plausible alternative origins.

No single pathway is presented as universal.

Slide 16 · Three proposed origin routes

Teratomatous

Mucin-producing glands within teratoma

Potential source in a subset

Brenner-associated

Mucinous glands associated with a Brenner tumor

Potential source in a subset

Müllerian

Müllerian epithelium differentiates toward mucin

Possible pathway for other tumors

Slide 17 · Multiloculation is the signature gross architecture

Multiple cystic spaces separated by delicate septa.

A single mass may contain numerous independent mucin-filled locules.

Gross configuration guides examination but does not alone determine behavior.

Original gross architecture schematic

Slide 18 · The locules contain gelatinous secretions

The cysts are filled with sticky, glistening material.

The fluid as glycoprotein-rich.

The luminal content reflects a mucin-secreting epithelial phenotype.

Original gross architecture schematic

Slide 19 · From secretory epithelium to cystic enlargement

Apical mucin production

Glycoprotein-rich luminal accumulation

Mucin-filled locules

This schematic links described histologic secretion to the gross appearance; It does not assert a measured growth rate.

Slide 20 · Large size is characteristic, not diagnostic of cancer

Mucinous ovarian neoplasms can form very large multicystic masses.

The textbook documents extraordinary examples weighing more than 25 kg.

Tumor size alone cannot distinguish cystadenoma, borderline neoplasm, and carcinoma.

Histologic architecture and invasion remain central to classification.

Slide 21 · The ovarian surface is usually not involved

Unlike serous tumors, primary mucinous tumors rarely involve the ovarian surface.

The expected gross pattern is predominantly cystic within the ovary.

Surface or extraovarian disease warrants a broader primary-versus-secondary assessment.

Original gross architecture schematic

Slide 22 · Primary mucinous tumors are usually unilateral

≈5%

Of primary mucinous cystadenomas and carcinomas are bilateral

Clinical implication

Bilateral mucinous ovarian masses demand exclusion of another primary

The approximately 5% figure refers to cystadenomas and carcinomas as stated in the morphology passage.

Slide 23 · Gross clues require microscopic correlation

Gross observation

What it supports

What it does not prove

Multiple cysts

Mucinous macroscopic pattern

Benignity

Gelatinous fluid

Mucin secretion

Primary ovarian origin

Large size

Substantial cystic growth

Invasion

Bilateral masses

Concern for secondary involvement

Definite metastasis

Slide 24 · Benign epithelium: Tall, columnar and nonciliated

Tall columnar lining cells surround cystic spaces.

Mucin accumulates toward the luminal (apical) surface.

Cilia are characteristically absent.

Schematic — not a histologic specimen

Slide 25 · Apical mucin is a functional morphologic clue

The cytoplasm shows apical mucin.

Mucin secretion accounts for the viscous cyst contents.

Cell shape and secretion are more informative together than either finding alone.

Schematic — not a histologic specimen

Slide 26 · Mucinous differentiation may resemble gut or gastric epithelium

Predominant patterns

Gastric-type differentiation

Intestinal-type differentiation

Less common pattern

Endocervical-type mucinous differentiation

Diagnostic principle

Recognize mucinous differentiation without assuming a gastrointestinal primary.

Slide 27 · Benign cystadenoma retains an orderly epithelial lining

The cystic spaces are lined by mucinous epithelium.

The benign category does not show the proliferative architecture defining a borderline tumor.

A smooth epithelial lining does not by itself address all regions of a heterogeneous mass.

Schematic — not a histologic specimen

Slide 28 · Borderline tumor: Epithelial stratification

Multiple epithelial cell layers replace the simple benign arrangement.

Architectural proliferation is more complex than cystadenoma.

Stratification is not synonymous with stromal invasion.

Schematic — not a histologic specimen

Slide 29 · Borderline tumor: Tufting into the lumen

Focal epithelial tufts project from the lining into a cyst or gland lumen.

This is an intraluminal proliferative change.

Interpret together with stratification, papillary growth, and invasion status.

Schematic — not a histologic specimen

Slide 30 · Borderline tumor: Papillary intraglandular growth

Papillae arise within glandular or cystic spaces.

The growth increases architectural complexity.

Papillary proliferation alone does not demonstrate destructive stromal infiltration.

Schematic — not a histologic specimen

Slide 31 · Borderline mucinous lesions may mimic bowel adenomas

Ovarian mucinous borderline tumor

Intestinal adenoma–like appearance

Shared architectural resemblance

Stratification

Tubular adenoma–like change

Morphologic analogy

Papillary or villous growth

Villous adenoma–like change

Morphologic analogy

Critical distinction

Ovarian site and full lesion assessment

Do not infer bowel origin from resemblance alone

Slide 32 · The borderline decision hinges on lack of invasion

Epithelial stratification / tufting

Papillary intraglandular growth

No stromal invasion identified

Borderline morphology is defined by proliferation; Carcinoma requires invasive morphology, not merely conspicuous intraluminal growth.

Slide 33 · Assess cytologic atypia separately from invasion

Question

Microscopic feature

Consequence

Is epithelium proliferative?

Stratification, tufting, intraglandular papillae

Supports borderline category

Is atypia marked?

Marked epithelial atypia

Consider intraepithelial carcinoma terminology

Is stromal invasion present?

Expansile or destructive invasive pattern

Supports mucinous carcinoma

Slide 34 · Expansile invasion: Confluent glandular growth

Crowded, confluent mucinous glands form an expansile growth pattern.

Robbins recognizes this architecture as a form of invasion.

Absence of an obvious desmoplastic response does not exclude carcinoma.

Schematic — not a histologic specimen

Slide 35 · Destructive invasion: Glands infiltrate desmoplastic stroma

Another invasive pattern involves stromal infiltration.

Desmoplastic stromal response accompanies destructive infiltration.

This pattern differs from confluent but relatively pushing glandular growth.

Schematic — not a histologic specimen

Slide 36 · Two invasive patterns can coexist in one carcinoma

Expansile

Confluent glandular growth

A recognized invasive pattern

Destructive

Desmoplastic stromal invasion

An alternative invasive pattern

Same lesion

Both architectures may be present

Evaluate all represented areas

Slide 37 · Intraepithelial carcinoma: Marked atypia, no invasion

Some authors use this designation for marked epithelial atypia without invasive features.

Severe epithelial cytology and stromal invasion should not be conflated.

The term as terminology used by some authors.

Schematic — not a histologic specimen

Slide 38 · Atypia and invasion are not interchangeable

Atypia

Stromal invasion

Interpretive category

Not prominent

Absent

Benign/borderline context by architecture

Marked

Absent

Noninvasive “intraepithelial carcinoma” terminology

Variable

Present

Mucinous carcinoma

Simplified educational matrix, not a replacement for complete diagnostic criteria.

Slide 39 · Morphologic spectrum need not be uniform within a mass

Benign region

Borderline region

Malignant region

The cited molecular study examined tumors containing more than one morphologic category. Regions in a single lesion can differ, so a single sampled field cannot define the whole tumor.

Slide 40 · Heterogeneity changes the diagnostic question

The source documents distinct benign, borderline, and malignant regions in some tumors.

A representative simple lining does not exclude more proliferative or invasive areas elsewhere.

An adequate morphologic assessment therefore asks whether higher-grade regions are present.

This is a sampling implication drawn from the source’s documented heterogeneity, not a numeric sampling protocol.

Slide 41 · Three questions organize microscopic assessment

Mucinous differentiation?

Borderline proliferation / atypia?

Expansile or destructive invasion?

Classify what the lesion is, then its proliferative severity, then whether it invades.

Slide 42 · An ovarian mucinous tumor may be secondary

Primary ovarian tumor

Usually unilateral

Primary ovarian mucinous neoplasm considered

Metastatic mucinous adenocarcinoma

Often requires active exclusion

Extraovarian primary must be investigated

Peritoneal mucinous disease

Appendiceal source often implicated

Do not default to ovarian primary

Slide 43 · Bilateral ovarian mucinous masses: The next diagnostic step

Mucinous masses in both ovaries

Consider metastasis

Investigate a nonovarian primary

Bilateral presentation must prompt exclusion of metastatic disease because most primary ovarian mucinous lesions are unilateral.

Slide 44 · Why the appendix matters

Mucinous epithelial neoplasms may originate in the appendix.

Almost all pseudomyxoma peritonei cases to an extraovarian primary, usually appendiceal.

Ovarian involvement may occur as part of disseminated appendiceal disease.

The historical assumption of frequent primary ovarian origin is not supported by the source’s current interpretation.

Slide 45 · Pseudomyxoma peritonei: An anatomic pattern of disease

Mucinous ascites

Peritoneal cystic epithelial implants

Adhesions and ovarian involvement

This is a clinical-pathologic syndrome rather than proof of a primary ovarian neoplasm.

Slide 46 · Mucinous ascites does not establish the primary site

Observation

Correct inference

Unsupported leap

Mucinous ascites

Mucin is present in the peritoneal cavity

The ovary generated it

Ovarian mucinous implants

Ovary is involved

Ovary is the primary

Appendiceal tumor identified

Potential nonovarian source

All ovarian lesions must be independent primaries

Slide 47 · Peritoneal disease can lead to obstruction

Mucinous peritoneal implants

Adhesions / increasing abdominal burden

Intestinal obstruction

Advanced pseudomyxoma peritonei may cause intestinal obstruction and death.

Slide 48 · Mucinous versus serous: Gross distribution

Feature

Mucinous

Serous

Cyst contents

Sticky gelatinous mucin

Serous fluid

Usual distribution

Primary tumors commonly unilateral

Bilaterality relatively common

Surface involvement

Rare in primary mucinous tumors

Can involve ovarian surface

Epithelial phenotype

Mucinous, usually nonciliated

Tubal-like; benign lining ciliated

Slide 49 · Borderline architecture differs by epithelial phenotype

Mucinous borderline

Epithelial stratification; Tufting; Intraglandular papillae

Can resemble intestinal adenomas

Serous borderline

Stromal papillary complexity and epithelial stratification

Serous/tubal-like epithelium

Shared diagnostic question

Is stromal invasion present?

Essential distinction from invasive carcinoma

Slide 50 · Symptoms usually follow tumor size or extraovarian involvement

Ovarian tumors can remain asymptomatic until large.

Abdominal distention or pain may reflect the size of a mucin-filled mass.

Urinary or gastrointestinal symptoms can follow compression or invasion.

Peritoneal dissemination creates additional complications beyond an ovarian mass.

Slide 51 · Localized noninvasive disease: Favorable reported outcome

>95%

Approximate 10-year survival for stage I noninvasive “intraepithelial carcinoma”

From the specific textbook morphology passage. Population, definitions, and modern staging comparability were not independently reverified.

Slide 52 · Localized invasive disease: Favorable reported outcome

≈90%

Approximate 10-year survival for stage I invasive mucinous malignancy

Stage I figure; Do not extrapolate to advanced stage or metastatic ovarian involvement.

Slide 53 · Spread beyond the ovary changes the prognosis

Extraovarian mucinous carcinomas as usually fatal.

The stage I outcome figures should not be applied to advanced disease.

Accurate discrimination from metastatic mucinous adenocarcinoma is especially consequential.

The source provides no numeric survival estimate here for advanced primary mucinous ovarian carcinoma.

Slide 54 · Case 1 · Multilocular cyst with simple mucinous lining

Illustrative findings: A large unilateral mucin-filled cystic ovarian mass.

Microscopy: Tall columnar nonciliated epithelium with apical mucin; Simple architecture.

Interpretation: Findings favor mucinous cystadenoma; Mass size does not alone justify carcinoma.

Recognize the benign epithelial pattern before considering growth-related symptoms.

Slide 55 · Case 2 · Stratification and intraglandular papillae

Illustrative findings: Mucinous ovarian epithelium shows stratification, tufting, and intraglandular papillary growth.

No stromal invasion is identified in the described sections.

Interpretation: A borderline mucinous pattern; Architecture is proliferative but noninvasive.

Proliferation is not itself stromal invasion.

Slide 56 · Case 3 · Crowded confluent mucinous glands

Illustrative findings: Mucinous glands grow in a tightly confluent pattern.

No conspicuous desmoplastic stromal response is described.

Interpretation: Expansile invasion can still establish mucinous carcinoma.

Do not require desmoplasia to recognize every invasive mucinous carcinoma.

Slide 57 · Case 4 · Bilateral ovarian lesions and gelatinous ascites

Illustrative findings: Bilateral ovarian mucinous masses, mucinous ascites, and peritoneal implants.

Diagnostic action: Seek an extraovarian primary, especially appendix.

Interpretation: Pseudomyxoma peritonei is not evidence of an ovarian primary by itself.

Establish tumor origin before assigning an ovarian primary diagnosis.

Slide 58 · Four recurrent interpretive errors

Error

Why it is wrong

Better question

“Large = malignant”

Huge benign mucinous masses occur

Is there invasion?

“Stratified = invasive”

Borderline tumors stratify

Where is stromal invasion?

“No desmoplasia = benign”

Expansile invasion exists

Are glands confluent?

“Ovary involved = primary”

Appendiceal metastasis is possible

Is a nonovarian primary present?

Slide 59 · Integrating morphology with site of origin

Identify mucinous phenotype

Classify proliferative / invasive pattern

Resolve primary ovarian vs metastatic

Each step answers a different question; A complete diagnosis requires integrating all three.

Slide 60 · The six essential conclusions

Most ovarian mucinous tumors are benign or borderline; Primary carcinoma is uncommon.

KRAS mutations occur across benign, borderline, and carcinoma categories.

Multiloculation, gelatinous mucin, and nonciliated columnar cells define typical morphology.

Borderline proliferation differs from expansile or destructive invasion.

Bilaterality and pseudomyxoma peritonei demand evaluation for extraovarian origin.

Stage and primary-site assignment are central to meaningful prognosis.

Slide 61 · Recommended reading

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th edition (2026).

Chapter: The Female Genital Tract; ovarian epithelial tumor and mucinous tumor sections.

All mechanisms, morphologic statements, and reported frequencies in this lecture are textbook-grounded.

Constructed cases and native vector drawings are educational schematics—not patient specimens.