Phyllodes Tumor

Slide 1 · Phyllodes tumor

Phyllodes Tumor

Breast fibroepithelial neoplasm | pathology lecture

Intralobular stromal origin • morphology • grading • clinical behavior

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · What this lecture establishes

Four learning outcomes

Recognize the intralobular stromal origin and biphasic structure.

Explain leaf-like architecture and stromal histologic grading.

Differentiate phyllodes tumor from fibroadenoma and related stromal lesions.

Connect tumor grade, excision margins, and routes of spread to clinical behavior.

Slide 3 · Breast stromal compartments

Breast stroma

Intralobular

Interlobular

Fibroadenoma + phyllodes

Other mesenchymal lesions

Distinct stromal origins → distinct tumor families

Slide 4 · Intralobular stroma produces biphasic tumors

Neoplastic stromal core

Nonneoplastic epithelial lining

+

Biphasic primary tumor

Proliferative stroma is accompanied by a reactive/nonneoplastic epithelial component.

Slide 5 · Interlobular stroma produces different tumors

Intralobular stroma

Interlobular stroma

Fibroadenoma

Lipoma

Phyllodes tumor

Myofibroblastoma

Biphasic: Stroma and epithelium

Stromal tumors without epithelial component

Slide 6 · Phyllodes is a stromal neoplasm

Neoplastic component

Intralobular stromal cells

Drives tumor architecture and grade

Forms proliferating stromal fronds

Associated component

Nonneoplastic epithelium

Covers stromal projections

Does not constitute the metastatic tumor

Slide 7 · Phyllodes is uncommon among fibroepithelial lesions

≈2.5%

Of breast fibroepithelial lesions

The relevant denominator is fibroepithelial lesions—not all breast neoplasms.

Fibroadenoma is much more common.

Slide 8 · Typical presentation is later than fibroadenoma

Entity

Typical presentation

Fibroadenoma

Women in their 20s and 30s

Phyllodes tumor

Most present in the sixth decade

Age contrast

Phyllodes peak is approximately 10–20 years later

Slide 9 · Clinical discovery: Palpable mass or imaging

Palpable presentation

Most tumors are detected as a mass.

A rapidly enlarging lesion warrants careful pathologic assessment.

Imaging detection

Other lesions are detected at mammography.

Clinical detection alone does not assign tumor grade.

Slide 10 · Tumor size spans a broad spectrum

A few centimeters

Massive lesion involving the entire breast

Size describes the macroscopic presentation; It is not synonymous with histologic grade.

Slide 11 · Fibroadenoma is the central comparator

Core observations

Both lesions arise from intralobular stroma.

Both contain nonneoplastic epithelium.

Both can produce cleft-like spaces and an intracanalicular pattern.

Discrimination depends especially on stromal histologic features.

Slide 12 · MED12 links the two fibroepithelial tumors

Intralobular stromal neoplasms

Fibroadenoma

Phyllodes tumor

Shared association: MED12 and RARA

Additional mutations are more often identified in phyllodes tumors: TERT, TP53, RB.

Slide 13 · MED12 participates in transcriptional control

MED12-encoded mediator subunit

RNA polymerase II transcriptional regulation

Altered stromal growth programs (hypothesis)

Altered hormone-regulated transcription as a possible mechanism, not a proven linear pathway.

Slide 14 · RARA is another shared genetic association

Core observations

RARA encodes retinoic acid receptor α.

RARA mutations with both fibroadenoma and phyllodes tumor.

RARA participates in transcriptional regulation.

A shared finding supports biological relatedness, not identical clinical behavior.

Slide 15 · Additional mutations are more common in phyllodes

Gene

Meaning stated by Robbins

TERT

Encodes telomerase

TP53

Listed among additional mutated genes

RB

Listed among additional mutated genes

Important boundary

Mutations alone do not provide a grading rule here

Slide 16 · Shared genetics does not erase morphologic distinctions

Shared

MED12 and RARA associations

Stromal origin

Biphasic epithelial–stromal composition

Distinctive for phyllodes

Higher propensity for additional gene mutations

Greater stromal cellularity and proliferation

Potential for infiltrative and metastatic behavior

Slide 17 · Gross lesions may contain bulbous protrusions

Core observations

The protrusions reflect nodules of proliferating stroma.

An epithelial covering remains over the stromal projections.

Large lesions may have an exaggerated lobulated or clefted architecture.

Slide 18 · Leaf-like architecture has a structural explanation

Lumen / cystic space

Epithelial lining

Proliferating stromal core

Stromal frond

Epithelial covering

Cleft / luminal space

Original schematic — not a histologic specimen

Slide 19 · Epithelial-lined clefts create the leaf-like pattern

Lumen / cystic space

Epithelial lining

Proliferating stromal core

Stroma pushes toward an open space

A thin epithelial lining remains

Repeated projections generate “leaf-like” contour

Original schematic — not a histologic specimen

Slide 20 · Fronds may extend into cystic spaces

Architecture

Bulbous stromal nodules

Epithelium covers projecting fronds

Projections may enter a cystic lumen

Interpretation

Describes spatial growth pattern

Does not by itself determine whether a tumor is malignant

Slide 21 · Leaf-like growth is not equivalent to malignancy

Finding: Leaf-like projections

Conclusion: Grade must be assessed separately

Comparable protrusions may occasionally occur in large fibroadenomas.

Slide 22 · The epithelium is not the neoplastic driver

Neoplastic stromal core

Nonneoplastic epithelial lining

+

Biphasic primary tumor

Only the stromal component is neoplastic and forms metastases.

Slide 23 · The stromal component determines grading

Examine stromal cells

Assess stromal proliferation and growth

Assign benign / borderline / malignant category

Biphasic architecture identifies the lesion; Stromal histology determines its class.

Slide 24 · Three histologic classes define the spectrum

Benign

Relatively lower stromal cellularity, atypia, and mitotic activity.

Borderline

Greater stromal atypia, cellularity, and mitotic activity than benign tumors.

Malignant

Infiltrative growth; Marked stromal overgrowth can obscure the epithelium.

Classification is based on stromal histology—not the leaf-like name alone.

Slide 25 · Benign phyllodes: Relatively modest atypia

Core observations

May closely resemble fibroadenoma.

Stroma is more cellular and mitotically active than typical fibroadenoma.

Benign cytologic features do not prevent occasional local recurrence.

Slide 26 · Borderline phyllodes: Intermediate stromal changes

Core observations

More conspicuous stromal atypia than in benign phyllodes tumors.

Greater stromal cellularity and mitotic activity.

Higher risk of local recurrence than the benign category.

Slide 27 · Malignant phyllodes: Infiltrative stromal tumor

Core observations

A widely infiltrative growth pattern may be present.

Marked stromal overgrowth can leave few residual epithelial structures.

Under these conditions, distinction from sarcoma is challenging.

Slide 28 · Stromal cellularity is a discriminating feature

Pattern

Relative stromal cellularity

Fibroadenoma

Delicate stroma in common patterns

Benign phyllodes

More cellular than fibroadenoma

Borderline phyllodes

More prominent than benign phyllodes

Malignant phyllodes

Assess alongside infiltration and overgrowth

Slide 29 · Stromal atypia informs the grading continuum

Benign profile: Less prominent atypia

Borderline: More conspicuous atypia

Atypia must be integrated with other stromal features; Robbins does not give numerical nuclear-atypia cutoffs in this section.

Slide 30 · Mitotic activity is evaluated in the stroma

Benign: Increased over fibroadenoma

Borderline: More mitotic activity than benign

This passage describes relative activity; It does not specify exact mitoses-per-area grading thresholds.

Slide 31 · Border infiltration is a malignant feature

Circumscribed example

Infiltrative interface: Schematic

Original schematic — not a histologic specimen

Slide 32 · Stromal overgrowth can obscure biphasic structure

Preserved biphasic pattern

Numerous epithelial-lined clefts

Stromal component remains recognizable

Marked stromal overgrowth

Few remaining epithelial profiles

Resembles a spindle-cell sarcoma

Slide 33 · Grade is a synthesis of multiple features

Feature

Benign

Borderline

Malignant

Cellularity

Mild relative increase

More conspicuous

Evaluate with full pattern

Atypia

Less prominent

More prominent

May be marked

Mitotic activity

Exceeds typical FA

Increased

May be conspicuous

Slide 34 · A characteristic shape cannot replace grading

Core observations

Architectural recognition identifies a phyllodes-like fibroepithelial tumor.

Cellular atypia, stromal cellularity, mitoses, and tumor border complete the assessment.

A large or leaf-like tumor need not be malignant.

Slide 35 · Surgical margin status has prognostic relevance

Tumor grade

Local recurrence

Margin status

Margin status as the most important predictor of local recurrence after excision.

Slide 36 · Fibroadenoma: A useful benign baseline

Growth and border

Usually well-circumscribed gray-white nodule

Delicate, sometimes myxoid stroma

Patent ducts or compressed clefts

Clinical pattern

Peak presentation in 20s–30s

Often multiple or bilateral

Hormonal responsiveness

Slide 37 · Pericanalicular and intracanalicular patterns

Pericanalicular

Intracanalicular

Stroma around patent ducts

Stroma compresses ducts into clefts

Original schematic — not a histologic specimen

Slide 38 · Phyllodes versus fibroadenoma

Dimension

Fibroadenoma

Phyllodes tumor

Stroma of origin

Intralobular

Intralobular

Epithelial component

Nonneoplastic

Nonneoplastic

Stromal cellularity

Usually delicate

Often more cellular

Mitotic activity

Generally less prominent

Greater in benign PT than FA

Typical age

20s–30s

Sixth decade

Behavior

Benign

Benign to malignant spectrum

Slide 39 · Why an intracanalicular pattern can mislead

Core observations

Fibroadenoma can compress ducts into cleft-like spaces.

Phyllodes tumors can display pronounced epithelial-lined leaf-like clefts.

An isolated cleft is insufficient: Examine the associated stromal features.

Slide 40 · Sarcoma enters the differential in high-grade lesions

Typical phyllodes

Biphasic epithelial–stromal tissue

May preserve epithelial-lined clefts

Stromal component drives biologic behavior

Sarcoma-like phyllodes

Marked stromal overgrowth

Few residual epithelial elements

A difficult differential with sarcoma

Slide 41 · Interlobular stromal tumors form a separate group

Core observations

Interlobular tumors lack the accompanying epithelial component.

They include benign mesenchymal lesions and uncommon malignant tumors.

The origin and composition differ from biphasic phyllodes tumor.

Slide 42 · Fibromatosis differs in composition and behavior

Feature

Phyllodes tumor

Breast fibromatosis

Origin

Intralobular stroma

Interlobular stromal lesion

Epithelial component

Present in primary lesion

Absent in tumor

Growth

Variable, may infiltrate

Irregular, infiltrating

Metastasis

Possible in malignant PT

Does not metastasize

Slide 43 · Angiosarcoma is not malignant phyllodes

Phyllodes tumor

Intralobular stromal origin

Biphasic primary tumor

Malignant variant spreads hematogenously

Angiosarcoma

An interlobular stromal malignancy

Vascular malignant neoplasm

May be sporadic or therapy-associated

Slide 44 · The benign category predominates

Up to 75%

Have benign cytologic features (Robbins wording)

These lesions may recur locally.

Benign phyllodes tumors do not metastasize in the source description.

Slide 45 · Benign tumors can still recur locally

Benign histologic features

Possible local recurrence

“Benign” here does not mean that complete local excision is clinically irrelevant.

Slide 46 · Borderline and malignant tumors recur more often

Core observations

Local recurrence increases relative to benign phyllodes tumor.

Tumor grade is relevant, but margin status is the strongest predictor specified.

Avoid conflating local recurrence with distant metastasis.

Slide 47 · Margin status predicts recurrence after excision

Tumor grade

Local recurrence

Margin status

Margin status as the most important predictor of local recurrence after excision.

Slide 48 · Distant spread is hematogenous

Primary phyllodes tumor

Bloodstream

Distant lesion

Metastases contain the neoplastic stroma—not the nonneoplastic breast epithelium.

Slide 49 · Malignant phyllodes can metastasize

≈1/3

Of uncommon malignant lesions develop distant hematogenous metastases

This statement refers to malignant phyllodes tumors—not all phyllodes tumors.

Robbins does not specify a time horizon in the supplied passage.

Slide 50 · Metastatic lesions contain only tumor stroma

Primary lesion

Neoplastic stroma

Nonneoplastic epithelial covering

Classically biphasic

Metastatic deposit

Neoplastic stromal component only

Epithelial component is absent in metastases

Slide 51 · Lymphatic dissemination is rare at every grade

Core observations

Lymphatic spread as rare regardless of grade.

This is mechanistically distinct from hematogenous dissemination.

Do not assume the axillary nodal pathway of ordinary breast carcinoma.

Slide 52 · Routine axillary dissection is contraindicated

Rare lymphatic spread

Do not perform routine axillary lymph node dissection

This point is explicitly stated for phyllodes tumors regardless of grade.

Slide 53 · Clinicopathologic behavior by class

Class

Local recurrence

Distant metastasis

Benign

Occasional

Not described

Borderline

Higher than benign

Not quantified in this passage

Malignant

Higher than benign

Hematogenous; Approximately one-third

Slide 54 · Case: A new mass in later adulthood

Teaching vignette (illustrative, not a real patient)

A woman in her sixth decade presents with a palpable breast mass. Why should phyllodes tumor be included among fibroepithelial possibilities?

Reasoning focus

Age modifies the differential.

The palpable finding alone cannot establish histologic grade.

Slide 55 · Case: Leaf-like fronds with bland stroma

Teaching vignette (illustrative, not a real patient)

An excision shows epithelial-lined leaf-like projections and relatively bland stroma. Does the architecture prove malignancy?

Reasoning focus

Identify the biphasic architecture.

Grade depends on stromal characteristics.

Slide 56 · Case: Increasing stromal atypia and mitoses

Teaching vignette (illustrative, not a real patient)

A fibroepithelial tumor has greater stromal cellularity, atypia and mitotic activity than a benign phyllodes tumor. Which category is suggested?

Reasoning focus

Relative stromal findings point toward borderline disease.

A single feature is not a complete grading algorithm.

Slide 57 · Case: Infiltrative spindle-cell overgrowth

Teaching vignette (illustrative, not a real patient)

A breast mass shows widely infiltrative stromal growth and very few epithelial elements. What diagnostic pitfall emerges?

Reasoning focus

Search for remaining epithelial structures.

Use the full morphologic and clinical context.

Slide 58 · Case: Local recurrence after excision

Teaching vignette (illustrative, not a real patient)

A borderline phyllodes tumor recurs at the excision site. Which reported pathologic factor most strongly predicts this event?

Reasoning focus

Local recurrence and distant spread are separate endpoints.

Record margin status accurately.

Slide 59 · Case: Stromal metastasis without epithelium

Teaching vignette (illustrative, not a real patient)

A distant lesion from a malignant phyllodes tumor contains only spindle-cell stroma. Is absence of epithelium unexpected?

Reasoning focus

Primary tumor is biphasic.

Metastatic component is stromal only.

Slide 60 · Case: Considering an axillary dissection

Teaching vignette (illustrative, not a real patient)

A phyllodes tumor is classified as malignant. Does the grade alone justify routine axillary node dissection?

Reasoning focus

Hematogenous spread is the clinically relevant distant route.

Do not use carcinoma-style nodal assumptions.

Slide 61 · Integrated diagnostic reasoning

Fibroepithelial breast lesion

Identify stromal + epithelial components

Evaluate stromal atypia, cellularity, mitoses, border, overgrowth

Grade → local recurrence / metastatic risk / clinical decisions

Slide 62 · Essential morphologic discriminators

Morphologic criteria, interpreted together

Biphasic lesion with neoplastic stromal component.

Leaf-like stromal fronds covered by nonneoplastic epithelium.

Increasing stromal cellularity, atypia and mitoses refine grade.

Infiltrative borders and stromal overgrowth favor malignancy.

Slide 63 · Essential clinical discriminators

Behavior follows the stromal tumor grade

Typical presentation in the sixth decade.

Benign lesions may recur but do not metastasize’ account.

Margin status strongly predicts local recurrence after excision.

Lymphatic spread is rare; Malignant distant spread is hematogenous.

Slide 64 · References and source boundaries

Primary text

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

Section: Stromal Tumors — Phyllodes Tumor.

Phyllodes Tumor; Morphology; Clinical Features; Fig. 23.25 caption.

This lecture uses source-based relative grading descriptions; numerical WHO cutoffs were not introduced.