Acinar Cell Carcinoma

Slide 1 · Acinar Cell Carcinoma

Pancreatic exocrine differentiation, morphology, diagnosis and clinical implications

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain the biological significance of acinar differentiation and zymogen granules.

Recognize characteristic clinical, gross and histologic patterns.

Select an immunohistochemical panel for a solid pancreatic neoplasm.

Integrate Wnt-pathway changes and other genomic findings with diagnostic limits.

Distinguish acinar carcinoma from its principal pancreatic mimics.

Slide 3 · Pancreatic epithelial lineages

Exocrine acinar cells

Digestive enzymes

Exocrine ductal cells

Fluid conduits

Endocrine islet cells

Hormone release

The tumor’s differentiation—not simply its organ of origin—defines the diagnostic category.

Slide 4 · What defines acinar cell carcinoma?

A malignant epithelial neoplasm with pancreatic acinar differentiation.

Neoplastic cells produce digestive enzymes and may retain zymogen granules.

Architecture ranges from obvious acini to solid and trabecular growth.

Confirmation of acinar products is crucial when morphology is ambiguous.

Slide 5 · Normal acinar organization

Schematic — not a histologic specimen

Secretory cells form small polarized units around a lumen.

Nuclei are typically positioned toward the basal cell pole.

Apical cytoplasm contains enzyme-rich secretory granules.

Slide 6 · Secretory granules explain the phenotype

Schematic — not a histologic specimen

Zymogen granules store pancreatic digestive enzyme precursors.

Tumor cells can preserve the machinery of enzyme synthesis.

The granular cytoplasm is a morphologic clue, not proof alone.

Slide 7 · From acinar program to diagnostic evidence

Acinar differentiation

Zymogen / enzyme synthesis

Granular cytoplasm + enzyme IHC

Histology suggests acinar differentiation; Immunophenotypic demonstration confirms it.

Slide 8 · Epidemiology: A rare pancreatic malignancy

Acinar cell carcinoma in approximately 1%–2% of adult pancreatic tumors.

Its rarity limits the size and certainty of many clinical series.

Incidence estimates vary with denominator, geography and case ascertainment.

Acinar carcinoma must not be equated with common pancreatic ductal adenocarcinoma.

Slide 9 · Age and sex distribution

Most cases occur in adults; The typical presentation is around later middle age.

Male predominance is described across multiple published series.

Rare pediatric cases occur and demand a broader differential diagnosis.

Demography supports context but cannot establish tissue lineage.

Slide 10 · Acinar carcinoma versus ductal carcinoma

Acinar cell carcinoma

Ductal adenocarcinoma

Enzyme-producing differentiation.

Often a large, fleshy, cellular mass.

Limited fibrous stroma is common.

Acinar markers support the diagnosis.

Duct-forming differentiation.

Desmoplastic infiltrative glands.

May produce marked stromal fibrosis.

Ductal phenotype dominates.

Slide 11 · Hereditary associations: Interpretation

Most acinar carcinomas are considered sporadic.

Rare syndromic or germline-associated cases have been reported.

A tumor variant does not itself prove a hereditary syndrome.

Germline evaluation depends on clinical context and genetic findings.

Slide 12 · Common symptoms are nonspecific

Abdominal pain or discomfort may accompany a pancreatic mass.

Unintentional weight loss and constitutional symptoms can occur.

Nausea or vomiting may reflect mass effect or advanced disease.

A symptom-based diagnosis is therefore unreliable.

Slide 13 · Why jaundice may be absent

Acinar carcinoma can arise anywhere within the pancreas.

Biliary obstruction depends on local anatomy and the pattern of growth.

Jaundice is reported less often than with pancreatic ductal adenocarcinoma.

Absence of jaundice does not imply indolent behavior.

Slide 14 · Imaging: Initial mass characterization

CT or MRI often demonstrates a solid pancreatic mass.

Larger lesions may show necrosis, hemorrhage or cystic degeneration.

A circumscribed appearance does not establish benignity.

Imaging defines anatomy; Tissue sampling defines differentiation.

Slide 15 · Clinical-to-pathologic diagnostic pathway

Pancreatic mass

On imaging

Tissue acquisition

EUS-guided sampling

Morphology + IHC

Lineage resolution

Consider molecular analysis on adequate tissue when clinically relevant.

Slide 16 · Serum lipase: Elevation versus syndrome

Some patients have elevated circulating lipase concentrations.

Biochemical elevation is not synonymous with metastatic fat necrosis syndrome.

The clinical syndrome in up to 15% of affected patients.

Test results require correlation with the mass, symptoms and morphology.

Slide 17 · Lipase-associated fat necrosis syndrome

Tumor releases lipase

Circulating enzyme activity

Distant adipose tissue injury

Subcutaneous fat necrosis / joint symptoms

The mechanistic link is ectopic enzymatic fat digestion, not simply tumor dissemination into fat.

Slide 18 · Metastatic fat necrosis: The clinical clues

Tender subcutaneous nodules may reflect fat necrosis.

Polyarthralgia or polyarthritis can accompany the systemic syndrome.

The “metastatic” designation describes a distant enzymatic effect.

The syndrome is distinctive but absent in most acinar carcinomas.

Slide 19 · Fat necrosis syndrome: Avoid two errors

Supported inference

Unsupported inference

Lipase release can produce distant adipose damage.

Skin and joint findings may guide the search for a pancreatic source.

The syndrome does not require tumor in the involved skin.

Every elevated serum lipase reflects acinar carcinoma.

Every acinar carcinoma has lipase hypersecretion.

Cutaneous nodules automatically represent tumor metastases.

Slide 20 · Gross growth pattern

Tumors are often large and relatively circumscribed.

A partial fibrous capsule may be present.

Cut surfaces are commonly soft, fleshy and tan to reddish.

Invasion can occur despite a deceptively circumscribed outline.

Slide 21 · Scant desmoplasia changes the texture

Acinar carcinomas are generally hypercellular.

The tumor often contains less fibrous stroma than ductal adenocarcinoma.

Consequently, a soft or friable gross consistency is characteristic.

The gross impression is a diagnostic clue, not a criterion in isolation.

Slide 22 · Hemorrhage, necrosis and cystic change

Rapidly growing large lesions may outstrip their blood supply.

Necrosis and hemorrhage can alter the cut surface and imaging appearance.

Secondary cystic spaces need not imply a primary cystic neoplasm.

Extensive sampling is important in heterogeneous lesions.

Slide 23 · Scanning magnification: The key pattern

High cellularity is typical of many pancreatic acinar carcinomas.

Thin stromal septa may divide broad tumor lobules.

Necrosis can be conspicuous at low magnification.

The low-power pattern helps distinguish a fleshy tumor from desmoplastic PDAC.

Slide 24 · Acinar pattern: Lumen and polarity

Schematic — not a histologic specimen

Small lumen-forming units resemble exocrine acini.

Tumor cells may form a single layer with basal nuclei.

Recognizable acini strongly suggest acinar differentiation.

Slide 25 · Solid pattern: Loss of obvious lumina

Schematic — not a histologic specimen

Large cohesive sheets can replace recognizable acini.

The neoplasm may appear monotonous at low power.

Acinar enzyme immunostains become central to classification.

Slide 26 · Glandular pattern: Dilated lumina

Schematic — not a histologic specimen

Expanded lumina produce a gland-like architecture.

Epithelial cells can be crowded or multilayered.

Do not infer ductal lineage solely from a glandular outline.

Slide 27 · Trabecular pattern: Endocrine mimic

Schematic — not a histologic specimen

Interlacing ribbons can resemble pancreatic neuroendocrine tumors.

Cellular polarity and cytoplasmic granules may provide clues.

A lineage-specific IHC panel is required in ambiguous cases.

Slide 28 · Architectural diversity of acinar carcinoma

Pattern

Dominant architecture

Potential diagnostic trap

Acinar

Small lumina, polarized cells

Resembles normal acini

Solid

Compact tumor-cell sheets

PanNET or solid tumor

Glandular

Widened lumina

Ductal carcinoma

Trabecular

Narrow ribbons of cells

PanNET

Slide 29 · Cytologic morphology

Tumor cells frequently possess abundant granular eosinophilic cytoplasm.

Round to oval nuclei are often basally oriented in well-formed acini.

A conspicuous single nucleolus is a useful clue.

Atypia and mitotic activity vary with tumor differentiation.

Slide 30 · Zymogen granules and PAS staining

Cytoplasmic granules contain enzyme-rich secretory material.

Granules may be PAS-positive and resistant to diastase digestion.

PAS-D positivity is supportive but not lineage-defining.

IHC for acinar products is more useful for definitive classification.

Slide 31 · Ultrastructural correlates

Rough endoplasmic reticulum

Golgi / secretory machinery

Electron-dense zymogen granules

Electron microscopy is biologically informative but rarely essential when acinar IHC is available.

Slide 32 · Heterogeneity creates sampling risk

Different architectural patterns can coexist within one tumor.

Small biopsies may sample only solid or neuroendocrine-like areas.

Necrosis and crush artifact can obscure differentiation.

Use a sufficiently broad marker panel rather than architecture alone.

Slide 33 · Immunohistochemistry: Diagnostic objective

Demonstrate pancreatic acinar enzyme synthesis in neoplastic cells.

Choose more than one marker when material and availability permit.

Interpret positivity in the context of distribution and morphology.

Screen competing endocrine and ductal lineages when indicated.

Slide 34 · Trypsin: Primary acinar marker

Trypsin immunoreactivity supports exocrine acinar differentiation.

It is among the most useful diagnostic markers for this entity.

Patchy labeling may occur in limited samples.

A negative result should trigger review of tissue and companion stains.

Slide 35 · Chymotrypsin: Complementary evidence

Chymotrypsin identifies a second exocrine acinar enzyme.

Combined trypsin/chymotrypsin testing improves recognition.

Reported sensitivity varies between series and methods.

Marker concordance strengthens an acinar-lineage interpretation.

Slide 36 · BCL10 antibody: An important nuance

A commonly used BCL10 clone cross-reacts with carboxyl ester lipase.

Thus, staining indicates acinar enzyme-associated antigenicity.

It should not be interpreted as evidence of BCL10 pathway activation.

Integrate with trypsin and histology, particularly on small biopsies.

Slide 37 · Lipase and amylase immunostains

Tumor enzyme expression is variable across acinar markers.

Lipase can provide supportive evidence of acinar differentiation.

Amylase is less consistently detected in acinar carcinomas.

Negative individual stains do not exclude the diagnosis.

Slide 38 · Cytokeratins confirm epithelial lineage

Pan-cytokeratins support carcinoma rather than a nonepithelial mass.

CK8 and CK18 expression is characteristic of acinar epithelial cells.

CK7 and CK19 are often absent but may be expressed focally.

CK7 positivity by itself cannot convert an acinar tumor into PDAC.

Slide 39 · Neuroendocrine markers: Focal pitfalls

Some acinar carcinomas express synaptophysin or chromogranin in a subset of cells.

Focal endocrine marker reactivity does not alone define a PanNET.

Coexpression must be interpreted with architecture and acinar enzyme staining.

The distinction matters because tumor types have different behavior.

Slide 40 · A focused IHC decision panel

Question

Useful tests

Interpretive caution

Is it epithelial?

Pan-cytokeratin

Does not specify acinar lineage

Is it acinar?

Trypsin, chymotrypsin, BCL10

Panel and pattern beat one stain

Is it endocrine?

Synaptophysin, chromogranin

Focal expression can occur in ACC

Is there an alternative lineage?

CK7/CK19 and context-dependent stains

Expression is not perfectly binary

Slide 41 · Practical approach to a solid pancreatic biopsy

Review architecture

Prove epithelial lineage

Document acinar products

Exclude major mimics

Integrate clinical imaging, biopsy adequacy, morphology and a deliberately selected IHC panel.

Slide 42 · PanNET: The closest everyday mimic

PanNET and acinar carcinoma may both be cellular and circumscribed.

Trabeculae and solid sheets can look similar on H&E.

A typical PanNET shows convincing neuroendocrine marker expression.

Diffuse acinar enzyme labeling supports acinar carcinoma instead.

Slide 43 · Acinar carcinoma versus PanNET

Acinar carcinoma

PanNET

Granular eosinophilic cytoplasm.

Prominent nucleolus may stand out.

Trypsin/BCL10 often support lineage.

Endocrine stains may be only focal.

Finely stippled nuclear chromatin may be evident.

Organoid or trabecular growth common.

Diffuse synaptophysin/chromogranin is typical.

Acinar markers generally absent.

Slide 44 · Acinar carcinoma versus PDAC

Acinar carcinoma

Pancreatic ductal adenocarcinoma

Cell-rich tumor with relatively scant stroma.

Acinar, solid or trabecular growth.

Enzyme-associated markers positive.

KRAS alterations less characteristic.

Infiltrative duct-forming glands.

Prominent desmoplastic response.

Duct-associated mucin phenotype.

KRAS pathway alterations common.

Slide 45 · Solid pseudopapillary neoplasm (SPN)

SPN can form solid or pseudopapillary pancreatic masses.

Nuclear β-catenin expression is typical of SPN.

Acinar carcinoma may also show Wnt-pathway alterations.

β-catenin staining alone is not sufficient to determine lineage.

Slide 46 · Pancreatoblastoma: Related acinar differentiation

Both tumors may exhibit acinar enzyme production.

Pancreatoblastoma occurs predominantly in pediatric patients.

Squamoid nests or morules are a key histologic clue to pancreatoblastoma.

Shared Wnt-pathway changes do not erase morphologic distinctions.

Slide 47 · Mixed acinar-neuroendocrine neoplasia

An acinar carcinoma may contain endocrine marker-positive cells.

Substantial, morphologically significant dual differentiation raises a mixed tumor.

A few synaptophysin-positive cells alone are insufficient.

Evaluate component extent on the whole specimen when possible.

Slide 48 · Differential diagnosis at a glance

Entity

Supporting clue

Best discrimination

Acinar carcinoma

Granular acinar / solid tumor

Trypsin / chymotrypsin / BCL10

PanNET

Organoid, salt-pepper chromatin

Broad endocrine phenotype

PDAC

Infiltrative glands + desmoplasia

Ductal phenotype + architecture

SPN

Pseudopapillae; nuclear β-catenin

Compatible phenotype; no acinar enzymes

Pancreatoblastoma

Squamoid morules, often pediatric

Morules + acinar phenotype

Slide 49 · Canonical Wnt control: Simplified pathway

APC-containing complex

Restrains β-catenin

Wnt activation / APC loss

Reduces degradation

β-catenin accumulation

Transcriptional signaling

APC loss-of-function and activating CTNNB1 mutations as routes to aberrant Wnt signaling.

Slide 50 · APC loss-of-function in acinar carcinoma

APC normally contributes to regulation of β-catenin abundance.

Loss of functional APC can promote constitutive Wnt signaling.

This mechanism in acinar carcinoma.

An alteration in one tumor does not imply a universal driver.

Slide 51 · CTNNB1 activation

CTNNB1 encodes β-catenin, a key Wnt-pathway effector.

Activating CTNNB1 mutations can increase β-catenin signaling.

Activating point mutations in acinar carcinoma.

Molecular findings must be placed alongside histology and IHC.

Slide 52 · Acinar and ductal carcinoma: Molecular context

Acinar carcinoma

Ductal adenocarcinoma

Heterogeneous genomic alterations.

Wnt pathway abnormalities occur.

DNA-repair gene defects in a subset.

Typical PDAC driver set often absent.

KRAS alteration is a frequent central event.

TP53/CDKN2A/SMAD4 patterns characteristic.

Different recurrent alterations shape biology.

Molecular profiles overlap imperfectly.

Slide 53 · Beyond Wnt: Genomic diversity

Comprehensive sequencing shows diverse alterations rather than one universal driver.

Homologous recombination repair genes may be altered in a subset.

Rare actionable kinase alterations or fusions have been reported.

Testing must be interpreted using tumor-specific evidence and current practice.

Slide 54 · DNA repair defects: Clinical interpretation

BRCA1/BRCA2/ATM alteration

Possible repair deficiency

Potential platinum sensitivity / matched treatment

Potential therapeutic relevance requires clinical validation; Genotype is not a guarantee of drug response.

Slide 55 · Actionable alterations: Evidence threshold

Molecular testing may reveal repair defects or targetable alterations.

Case series and reports suggest benefit from some matched treatments.

Many therapy associations lack prospective acinar-specific validation.

Report predictive assertions with their level of evidence.

Slide 56 · Mismatch repair and immunotherapy

Deficient mismatch repair / high microsatellite instability is uncommon but reported.

These findings may have therapeutic implications across tumor types.

The assay and interpretation should follow validated laboratory methods.

Do not infer immunotherapy sensitivity from histologic subtype alone.

Slide 57 · Local invasion and metastatic routes

A circumscribed tumor can still invade pancreas-adjacent structures.

Regional lymph nodes and liver are important metastatic sites.

Staging incorporates anatomic extent and distant disease.

Extent of disease directly determines resectability discussions.

Slide 58 · Surgical decision: Conceptual framework

Diagnosis and staging

Assess metastasis + vascular involvement

Resectability and multidisciplinary review

For localized, operable disease, resection is the principal potentially curative approach.

Slide 59 · Treatment: Evidence is limited by rarity

Radical resection is commonly favored when disease is resectable.

Recurrence after surgery remains a major clinical problem.

The optimal postoperative systemic regimen is not established.

Unresectable-disease therapy is based mainly on retrospective evidence.

Slide 60 · Systemic therapy: Interpret cautiously

Retrospective reports support activity of fluoropyrimidine/platinum-containing regimens.

Some advanced cases respond to combination regimens such as FOLFIRINOX.

Matched molecular therapy may be considered for qualifying alterations.

None of these observations replaces individualized oncology assessment.

Slide 61 · Prognosis: Different from ductal cancer

Outcomes are generally more favorable than for pancreatic ductal adenocarcinoma.

Nevertheless, acinar carcinoma is an aggressive malignant neoplasm.

Stage, resection status and disease recurrence remain important.

Published survival estimates differ across cohorts and treatment eras.

Slide 62 · Case 1 — solid pancreatic mass

A pancreatic biopsy shows a hypercellular neoplasm with minimal stroma and solid-to-trabecular growth. Synaptophysin is focal; Cytokeratin is positive.

Which lineage-defining tests should be prioritized?

Slide 63 · Case 1 — diagnostic resolution

Use trypsin and/or chymotrypsin with BCL10 to evaluate acinar differentiation.

Interpret focal synaptophysin cautiously; It does not establish PanNET.

Correlate stains with granularity, nucleoli and growth architecture.

Classify the tumor by the integrated morphologic and immunophenotypic pattern.

Slide 64 · Case 2 — systemic lipase effect

A patient with a pancreatic mass develops tender subcutaneous nodules and arthralgias. Serum lipase is elevated.

Which paraneoplastic mechanism should be considered?

Slide 65 · Case 2 — mechanism and limits

A lipase-secreting acinar carcinoma can cause metastatic fat necrosis syndrome.

Circulating lipase may injure adipose tissue at distant sites.

The presentation should prompt targeted diagnostic evaluation, not presumptive diagnosis.

Most acinar carcinomas do not produce the complete clinical syndrome.

Slide 66 · Case 3 — β-catenin is not enough

A solid pancreatic neoplasm shows nuclear β-catenin labeling. Imaging and morphology do not securely distinguish acinar carcinoma from SPN.

What additional evidence is necessary?

Slide 67 · Case 3 — avoid a marker trap

Nuclear β-catenin is not exclusive to one pancreatic neoplasm.

Assess the architecture and phenotype expected for SPN.

Demonstrate or exclude acinar differentiation using enzyme-associated stains.

Resolve the diagnosis on the full panel, not the Wnt pathway alone.

Slide 68 · Integrated diagnosis in four questions

Is the mass epithelial?

Does it produce acinar enzymes?

Could a mimic explain the pattern?

Is the report clinically actionable?

A defensible diagnosis links cellular differentiation to morphology, IHC and clinical context.

Slide 69 · Essential morphologic takeaways

Acinar differentiation may be architecturally overt or deceptively subtle.

Solid, glandular and trabecular patterns overlap with other pancreatic tumors.

Abundant granular cytoplasm, conspicuous nucleoli and scant stroma are useful clues.

Definitive diagnosis relies on evidence of acinar enzyme expression.

Slide 70 · Essential clinical and molecular takeaways

This tumor is uncommon and biologically distinct from PDAC.

Lipase-related metastatic fat necrosis is characteristic but infrequent.

APC/CTNNB1-related Wnt activation is one documented molecular mechanism.

Selected molecular findings may matter therapeutically, but evidence varies.

Slide 71 · Core reference sources

Source

Contribution

Robbins, Cotran & Kumar, 11th ed., ch. 19 (2026)

Primary excerpt: rarity, acinar secretions, fat necrosis, APC/CTNNB1

La Rosa et al., Front Med. 2015;2:41

Morphology, differential diagnoses, Wnt biology

Calimano-Ramirez et al., WJG. 2022;28:5827–5844

Pathology and immunohistochemical differentials

Ikezawa et al., JJCO. 2024;54:271–281

Clinical features, genomics, and treatment evidence