Lobular Carcinoma In Situ

Slide 1 · Lobular carcinoma in situ

Lobular carcinoma in situ

Morphology • molecular biology • clinicopathologic interpretation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Recognize classic LCIS and relate its morphology to loss of cell adhesion.

Distinguish lobular neoplasia from ductal carcinoma in situ and invasive carcinoma.

Interpret E-cadherin, hormone receptor status, and bilateral risk.

Apply Robbins-based principles to core biopsy management.

Slide 3 · Where LCIS belongs in breast pathology

Noninvasive lesion

Neoplastic epithelial proliferation remains within the ductal–lobular system.

Lobular phenotype

Discohesive epithelial cells; Loss of E-cadherin is characteristic.

Risk indicator

Subsequent invasive carcinoma can occur in either breast.

Slide 4 · The defining biological feature

Neoplastic cells are dyscohesive

They proliferate within ducts and lobules without the cohesive epithelial arrangement of normal breast tissue.

Slide 5 · The terminal duct–lobular unit is the setting

Breast carcinoma in situ develops within the terminal duct–lobular unit.

A terminal duct branches into groups of acini (the lobule).

LCIS expands acini while recognizable lobular architecture remains.

The intact boundary distinguishes an in situ proliferation from invasion.

Slide 6 · Normal acini versus acini expanded by LCIS

Normal lobule

Classic LCIS

Schematic: Terminal duct–lobular units, not histologic specimens

Slide 7 · What “in situ” does—and does not—mean

Intact peripheral boundary

Cells remain in situ

Schematic; Peripheral line represents the basement membrane

Slide 8 · Lobular neoplasia is a morphologic continuum

Atypical lobular hyperplasia

Limited involvement by discohesive cells

Classic LCIS

More extensive filling and expansion of acini

Invasive lobular carcinoma

Neoplastic cells infiltrate beyond in situ boundaries

These lesions can have similar cytology; Extent and tissue compartment are decisive.

Slide 9 · Atypical lobular hyperplasia versus classic LCIS

Atypical lobular hyperplasia

Small, round, dyscohesive neoplastic cells.

Histologically identical cellular phenotype to classic LCIS.

More limited extent within acini.

Classic LCIS

Same characteristic dyscohesive cell type.

Cells fill and expand more than half of acini in an involved lobular unit.

Extent supports the LCIS designation.

Slide 10 · The threshold is architectural extent

More than half of acini

The classic LCIS description uses filling and expansion of more than half the acini in a terminal duct–lobular unit.

Slide 11 · Cell identity alone cannot establish invasion

Cells in atypical lobular hyperplasia, LCIS, and invasive lobular carcinoma may look alike.

LCIS is distinguished from invasion by its confinement to ducts and lobules.

Evaluation requires tissue architecture and the neoplastic cell distribution.

Cytologic similarity does not make the three diagnoses interchangeable.

Slide 12 · LCIS is commonly an incidental finding

Most classic LCIS is discovered in tissue sampled for another reason.

The lesion seldom produces the microcalcifications that prompt mammography-directed biopsy.

Stromal reactions causing mammographic densities are also usually absent.

Clinical and imaging silence follows from its morphology.

Slide 13 · Why screening often does not identify classic LCIS

Classic LCIS

Limited necrosis and secretory activity

Typical imaging consequence

Calcification is generally absent

Presentation

Often detected incidentally at biopsy

This describes the usual pattern; Aggressive variants may calcify.

Slide 14 · Reported frequency has not risen with screening

Robbins gives LCIS as approximately 1%–6% of all carcinomas in its discussion.

Unlike mammographically visible DCIS, LCIS detection is often incidental.

Its incidence has been unchanged by mammographic screening.

Interpret this as a source-specific epidemiologic statement, not a new population estimate.

Slide 15 · Classic LCIS and DCIS differ in detectability

Classic LCIS

Rare calcifications.

Rare stromal reaction producing a radiologic density.

Typically not the target of screening biopsy.

DCIS

Frequently associated with calcifications.

Usually identified on mammography.

May occasionally produce a density or nipple-related presentation.

Slide 16 · Bilateral involvement is an important clue

LCIS involvement on bilateral sampling

LCIS

20%–40%

0%

10%

20%

30%

40%

50%

DCIS

10%–20%

0%

10%

20%

30%

40%

50%

Intervals are reported ranges, not estimates of an individual patient’s risk.

Slide 17 · What bilateral involvement means

LCIS is not necessarily restricted to the breast in which it is discovered.

When both breasts are sampled, LCIS is reported in both in 20%–40% of cases.

By comparison, bilateral DCIS in 10%–20%.

These are frequencies of bilateral LCIS/DCIS findings on bilateral sampling, not lifetime invasive-cancer risks.

Slide 18 · Dyscohesion arises from failed cell adhesion

Adhesion preserved

Cell–cell contact

Adhesion disrupted

Rounded, dyscohesive cells

Schematic of E-cadherin-mediated adhesion

Slide 19 · Normal function of E-cadherin

E-cadherin is a transmembrane cell-adhesion protein.

It helps breast epithelial cells maintain lateral contact with neighbors.

E-cadherin-associated proteins support functional epithelial adhesion.

Loss of this system explains rounded, loosely attached LCIS cells.

Slide 20 · From adhesion loss to the LCIS appearance

Molecular change

E-cadherin pathway loses function

Cell phenotype

Cells round up and become dyscohesive

Histology

Loosely cohesive cells expand acini

Causal direction follows the explanation given.

Slide 21 · CDH1 is the principal gene

CDH1 encodes the E-cadherin adhesion protein.

The gene at chromosome 16q22.1.

Mutation or deletion of CDH1 commonly underlies E-cadherin loss.

This is an adhesion-related tumor suppressor pathway in glandular epithelium.

Slide 22 · Deletion and mutation are alternative routes

CDH1 mutation

Altered CDH1 sequence can produce loss of normal E-cadherin function.

The functional effect is impaired intercellular adhesion.

CDH1 deletion

Loss of genomic material may remove or disrupt CDH1.

Chromosome 16q alterations also link LCIS with the low-grade pathway.

Slide 23 · A negative E-cadherin stain is biologically meaningful

Loss of membranous E-cadherin expression supports a lobular phenotype.

Dyscohesive rounded morphology and loss of E-cadherin are concordant observations.

Normal epithelial cells may retain expression and provide an internal contrast.

Immunophenotype must be interpreted with tissue architecture.

Slide 24 · E-cadherin staining: Conceptual pattern

Adjacent normal luminal cells

LCIS cells

Membranous E-cadherin retained

E-cadherin expression lost

Schematic of the staining distinction — not an IHC photomicrograph

Slide 25 · Rare non-CDH1 causes of failed adhesion

Loss of E-cadherin function is usually the basis of dyscohesion, but not universally.

Robbins also describes rare dysfunction in proteins needed for E-cadherin-mediated adhesion.

β-catenin is named as one such associated protein.

A mechanistic absence of adhesion need not always reflect direct CDH1 loss.

Slide 26 · LCIS is linked to the low-grade pathway

Low-grade breast neoplasia includes precursor lesions, classic LCIS, and some well-differentiated invasive cancers.

Chromosome 16q deletion is a shared genomic alteration in this pathway.

Atypical lobular hyperplasia also demonstrates E-cadherin loss.

These similarities support a biological relationship across morphologic categories.

Slide 27 · Molecular parallels with invasive carcinoma

LCIS may show a mutation spectrum like that of a synchronous invasive carcinoma.

Shared molecular alterations suggest related neoplastic lineages.

Molecular similarity does not establish invasion in a particular biopsy.

The histologic distinction between in situ and invasive carcinoma remains essential.

Slide 28 · Classic LCIS: Uniform epithelial population

A relatively monotonous population of epithelial cells fills involved acini.

Nuclei are round or oval rather than strikingly pleomorphic.

Nucleoli are generally small.

The lobular outlines can still be identified despite luminal expansion.

Slide 29 · Classic LCIS expands, rather than obliterates, lobules

Unexpanded terminal lobule

Lobule expanded by LCIS

Schematic: Terminal duct–lobular units, not histologic specimens

Slide 30 · How the nuclear features fit the diagnosis

Uniform nuclear size and shape are characteristic of classic LCIS.

Round-to-oval nuclei are seen within dyscohesive epithelial cells.

Small nucleoli accompany the relatively bland cytology.

Architectural extent distinguishes classic LCIS from more limited lobular atypia.

Slide 31 · Mucin-containing signet-ring cells can occur

Mucin-positive signet-ring cells are commonly found in classic LCIS.

Mucin within cytoplasm can displace a nucleus to the periphery.

Their presence should be interpreted with the characteristic lobular architecture.

A signet-ring appearance alone does not prove an invasive process.

Slide 32 · Pagetoid spread can involve the ducts

Lobular neoplastic cells

Dyscohesive epithelial population

Ductal extension

Cells occur beneath the luminal layer

Pagetoid distribution

Cells lie between luminal cells and basement membrane

Pagetoid ductal spread is not the same diagnosis as Paget disease of nipple skin.

Slide 33 · Pagetoid ductal spread versus nipple Paget disease

Pagetoid spread in LCIS

Neoplastic cells track beneath the ductal luminal epithelium.

Seen commonly as duct involvement in lobular neoplasia.

Defined by an intraductal location.

Paget disease of nipple

Involves the epidermis of the nipple.

Usually arises in association with DCIS.

Nipple Paget disease is rare with LCIS.

Slide 34 · Classic LCIS usually lacks necrosis

Classical LCIS is typically not associated with necrosis.

Intraluminal secretory activity is generally absent.

Without these processes, calcifications are uncommon.

The lack of calcification helps explain incidental presentation.

Slide 35 · Pleomorphic LCIS differs from the classic form

Classic LCIS

Usually uniform, relatively bland nuclei.

Necrosis and calcifications generally absent.

Commonly an incidental histologic diagnosis.

Pleomorphic LCIS

Aggressive variant with larger pleomorphic cells.

May show necrosis and calcifications.

Requires a different clinical management approach.

Slide 36 · Calcifications do not exclude lobular disease

The usual absence of calcifications applies chiefly to classic LCIS.

Pleomorphic LCIS can produce necrosis and calcifications.

An imaging-visible lesion can therefore still be lobular in phenotype.

Interpret imaging together with histologic subtype, rather than relying on a single screening expectation.

Slide 37 · Hormone receptor profile of LCIS

ER

Almost always expressed in LCIS

PR

Almost always expressed in LCIS

HER2

Usually negative in LCIS

Pattern reported for LCIS; Not a stand-alone diagnostic criterion

Slide 38 · ER and PR positivity connects to biology

LCIS almost always expresses estrogen and progesterone receptors.

The hormone receptor phenotype resembles that of lesions in the low-grade breast pathway.

Hormone receptor expression does not by itself distinguish in situ from invasive carcinoma.

Receptor results require integration with morphology and cell adhesion phenotype.

Slide 39 · LCIS and DCIS: Essential diagnostic differences

Feature

Classic LCIS

DCIS

Cell cohesion

Dyscohesive

Typically cohesive epithelial proliferations

E-cadherin

Usually lost

Distinguishing expression pattern retained

Screening

Often incidental

Frequently mammographic calcifications

Risk distribution

Either breast

Often local ipsilateral recurrence risk

Slide 40 · What immunohistochemistry can clarify

E-cadherin can support lobular versus ductal epithelial differentiation.

ER and PR describe a common receptor profile of LCIS.

HER2 is usually negative in LCIS.

Neither adhesion nor receptor staining replaces evaluation for invasion.

Slide 41 · Classic lobular neoplasia: An interpretive sequence

Identify architecture

Lobular/acinar extent and boundaries

Assess cells

Uniform, discohesive phenotype

Integrate stains

E-cadherin loss and receptor profile

Classify

ALH, LCIS, or invasion by extent/site

Schematic reasoning aid derived from morphologic distinctions in the source; Not a formal clinical algorithm.

Slide 42 · ALH versus LCIS: The decisive observation

What they share

Round, relatively uniform epithelial cells.

Loss of cohesion; Commonly loss of E-cadherin.

Confinement to the ductal–lobular system.

What differs

ALH is histologically less extensive.

Classic LCIS fills and expands >50% of acini in a lobular unit.

Classification depends on extent, not a novel cell type.

Slide 43 · LCIS versus invasive lobular carcinoma

LCIS

Cells occupy ductal and lobular compartments.

The in situ basement membrane boundary remains.

An in situ risk lesion with possible local precursor relationship.

Invasive lobular carcinoma

Cells breach the in situ compartment and infiltrate stroma.

Cytology may resemble that of LCIS.

Invasion is an architectural, not merely nuclear, diagnosis.

Slide 44 · LCIS predicts risk in either breast

LCIS identified

Future invasive carcinoma risk is elevated

Ipsilateral breast

Risk is slightly higher in the same breast as the LCIS.

Contralateral breast

The opposite breast is also at increased risk.

Slide 45 · Relative risk: Eight- to tenfold

8–10×

An 8- to 10-fold higher invasive breast carcinoma risk in patients with classic LCIS than in the general population.

Slide 46 · Relative risk is not certainty of cancer

An 8–10× relative risk compares populations, not a prediction for an individual patient.

Relative risk must be distinguished from the annual rate at which cancers appear.

Most risk discussions require patient-level context beyond a single tissue finding.

LCIS is clinically important even though progression to invasion is not inevitable.

Slide 47 · Reported invasive carcinoma rate

Approximately 1% per year

Robbins gives this approximate annual rate following classic LCIS; It is not a guarantee of a constant personal risk.

Slide 48 · The annual rate resembles low-grade DCIS

Classic LCIS

Invasive carcinoma appears at about 1% per year description.

Subsequent disease may arise in either breast.

Untreated low-grade DCIS

A similarly approximate annual invasion rate.

Invasive carcinomas commonly occur in the same breast location.

Slide 49 · LCIS is both a risk marker and a possible precursor

Bilateral risk supports the interpretation of LCIS as a marker of general breast susceptibility.

Shared mutations with synchronous invasive carcinoma support a precursor relationship in some cases.

These two roles are not mutually exclusive.

The distinction matters when interpreting the value of local excision.

Slide 50 · Why removing LCIS has an uncertain effect

LCIS conveys risk to both breasts, not only the sampled focus.

It remains unclear whether surgical removal reduces that risk.

This differs from the rationale for routine local treatment of DCIS.

Management therefore depends on LCIS subtype and clinicoradiologic context.

Slide 51 · Classic LCIS on core biopsy: Imaging correlation

Core biopsy

Classic LCIS identified

Imaging review

Pathology explains or is concordant with the finding

One possible approach

Active surveillance

Surveillance in selected imaging-concordant classic LCIS; This is not a patient-specific recommendation.

Slide 52 · Why concordance matters in core biopsy

A classic LCIS diagnosis must be considered in the context of the lesion being sampled.

In imaging-concordant cases, a very low probability of associated invasion.

This explains why active surveillance may be appropriate for selected classic LCIS.

The textbook does not supply a universal rule for all discordant cases.

Slide 53 · Aggressive LCIS variants are treated differently

Subtype assessment

Classic versus aggressive variant

Concordant classic LCIS

Active surveillance is an option.

Pleomorphic / aggressive variant

Surgical excision is the approach.

Slide 54 · Reasons to excise pleomorphic LCIS

Pleomorphic LCIS is classified among more aggressive lobular in situ variants.

It may present with calcifications and necrosis, unlike classic LCIS.

Robbins recommends surgical excision for more aggressive variants.

Do not transfer the classic LCIS surveillance approach automatically to pleomorphic LCIS.

Slide 55 · Other risk-management strategies

Robbins mentions mastectomy in selected LCIS cases.

The text also identifies endocrine therapy as an option for some patients.

The adjacent precursor-lesion discussion names estrogen antagonists such as tamoxifen for risk reduction.

These choices require individual clinical evaluation; This lecture does not prescribe therapy.

Slide 56 · Local disease versus bilateral-risk strategy

DCIS — predominantly local strategy

Subsequent invasive disease usually arises at the same site.

Complete surgical removal is a central component of treatment.

Local recurrence is a major management concern.

LCIS — bilateral-risk perspective

Subsequent invasive disease can arise in either breast.

Benefit of excision of classic LCIS is less certain.

Risk reduction and surveillance become key considerations.

Slide 57 · Case 1: An incidental lobular lesion

A screening-guided breast core biopsy performed for an unrelated radiologic finding contains small, uniform, loosely cohesive cells filling most acini. E-cadherin expression is lost. Imaging and pathology are concordant. Which interpretation best fits Robbins?

Classic LCIS with surveillance as a possible option

Invasive lobular carcinoma established by E-cadherin loss alone

Mandatory excision because all LCIS behaves like high-grade DCIS

Slide 58 · Case 1: Interpretation

Classic LCIS; Surveillance may be an option

Characteristic dyscohesive cells fill/expand most acini.

E-cadherin loss supports the lobular phenotype.

No invasion is established by these data.

Concordant classic LCIS on core biopsy is eligible for surveillance in selected cases.

Slide 59 · Case 2: Calcifying in situ lobular lesion

A breast lesion has calcifications and necrosis. Histologic review identifies a pleomorphic lobular epithelial proliferation. Which source-based response is most appropriate?

Classify it as classic LCIS because lobular lesions never calcify

Recognize an aggressive LCIS variant and consider surgical excision

Conclude automatically that the lesion is invasive carcinoma

Slide 60 · Case 2: Interpretation

Consider pleomorphic LCIS and surgical excision

Pleomorphic LCIS may show necrosis and calcifications.

These features contradict the usual classic LCIS presentation, not the lobular diagnosis.

Excision of aggressive variants from surveillance in selected classic LCIS.

Slide 61 · Morphologic synthesis

Cells

Uniform round/oval cells, small nucleoli, dyscohesion

Architecture

Acini filled and expanded; Pagetoid ductal spread possible

Stains

E-cadherin usually lost; ER/PR often positive; HER2 usually negative

Applies principally to classic LCIS, with variant-specific exceptions.

Slide 62 · Clinical synthesis

Recognition

Often incidental; Classic form rarely calcifies

Risk

8–10× increased risk; Either breast; Approximately 1%/year

Management

Surveillance can be considered for concordant classic LCIS; Aggressive variants are excised

Statistics and options reproduce Robbins, not externally updated guidance.

Slide 63 · Source and further reading

Robbins, Cotran & Kumar. Pathologic Basis of Disease, 11th edition (2026), Chapter 23: The Breast.

LCIS subsection, printed page 953, continuing onto page 954.

Relevant parent sections: precursor lesions, carcinoma in situ, and DCIS.

Original textbook Fig. 23.14 should be consulted for genuine H&E and E-cadherin immunohistochemical examples.