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WHO reporting system for pancreaticobiliary cytopathology


Editorial Board Members: Wei Chen, M.D., Ph.D., Bonnie Choy, M.D.
Deputy Editor-in-Chief: Catherine E. Hagen, M.D.
Victoria M. Jones, M.D.
Derek Allison, M.D.

Last author update: 7 April 2022
Last staff update: 24 November 2023

Copyright: 2021-2024, PathologyOutlines.com, Inc.

PubMed Search: Pancreas Papanicolaou system

Victoria M. Jones, M.D.
Derek Allison, M.D.
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Table of Contents
Definition / general | Essential features | Techniques for cytologic sampling of pancreatic and bile duct lesions | Metrics | Papanicolaou system for reporting pancreaticobiliary cytology | Diagrams / tables | Laboratory | Case reports | Cytology description | Cytology images | Additional references | Board review style question #1 | Board review style answer #1 | Board review style question #2 | Board review style answer #2
Cite this page: Jones V, Allison D. WHO reporting system for pancreaticobiliary cytopathology. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/pancreaspapanicolaousystem.html. Accessed December 3rd, 2024.
Definition / general
  • The Papanicolaou Society of Cytopathology (PSC) developed guidelines in 2014 for interpreting and reporting pancreaticobiliary cytology
  • Standardization provides uniform diagnostic reporting, reproducibility and clinically relevant risk stratification
  • Resulted in a 6 tiered reporting system: nondiagnostic, negative (for malignancy), atypical, neoplastic (benign or other), suspicious (for malignancy) and positive or malignant
Essential features
  • Internationally adopted recommendations for sampling, diagnosing and managing pancreaticobiliary cytology lesions
  • 6 tiered categorical system resulting in overall improved sensitivity / specificity and risk stratification
  • Risks of malignancy inform multidisciplinary patient care
Techniques for cytologic sampling of pancreatic and bile duct lesions
Metrics
  • Risk of malignancy (ROM) = total number FNA specimens that proved malignant on follow up / total number of surgical resections and clinical follow ups (Cancer Cytopathol 2020;128:29)
    • Average ROM for each diagnostic category (next section) is provided by the Saieg and Pitman review of several studies (Diagn Cytopathol 2020;48:494)
  • Diagnostic variation due to:
    • Operator skill, experience and medical device
    • Variation in prevalence of pathology and patient populations
    • Limited availability of ancillary tests (Cytopathology 2020;31:564)
    • Absence of rapid on site assessment (ROSE) (Oncotarget 2017;8:8154)
Papanicolaou system for reporting pancreaticobiliary cytology
  • Category I: nondiagnostic
    • Provides no useful diagnostic or useful information about the solid or cystic lesion sampled
    • Entities include:
      • Cells obscured by artifacts such as hemorrhage or necrosis
      • Pure gastrointestinal contamination indicates missed lesion
      • Acellular specimens obtained from cyst with no evidence of mucinous etiology
      • Benign pancreatic parenchyma with well defined mass on imaging
    • Ancillary testing may result in reduced utilization of this category for cystic lesions (Diagn Cytopathol 2017;45:303)
    • Average ROM: 23.1%
    • Management: reassess or repeat sampling
  • Category II: negative (for malignancy)
    • Contains adequate cellular or extracellular tissue to evaluate or define a lesion that is identified on imaging
      • Minor degree of loss of cell or nuclear polarity
      • No cytologic atypia observed
    • Entities include:
      • Acute, chronic or autoimmune pancreatitis
      • Pseudocyst
      • Lymphoepithelial cyst
      • Splenule or accessory spleen
      • Benign pancreatic parenchyma with no discrete mass on imaging
    • Ancillary tests such as amylase and carcinoembryonic antigen cyst fluid analysis can be helpful for cystic lesions (Diagn Cytopathol 2017;45:303)
    • Increased false negative rate in biliary brushings due to underlying inflammatory lesions and subepithelial tissue entrapped within desmoplasia
    • Average ROM: 8.2%
    • Management: respective conservative care unless patients have irretractable symptoms or high risk of malignancy
  • Category III: atypical
    • Cells present with cytoplasmic, nuclear or architectural features that are not consistent with normal or reactive changes of the pancreas and bile ducts and insufficient to classify as neoplasm or suspicious for high grade malignancy
      • Slight nuclear membrane irregularity, nuclear crowding with minor degree of overlap, nuclei haphazardly occupy lower 66% of the cell at the base, minimal degree of anisonucleosis (2:1), near normal N:C ratio, parachromatin clearing, background smear is clean or contains red blood cells
      • Also includes entities with abundant intracytoplasmic mucin in the epithelium without overt cytologic atypia
      • Absent features: necrosis, true nuclear molding, macronucleoli and features of malignancy
    • Category with the widest range of reported ROM: 28 - 100%, average of 46.8%
    • Management: repeat sampling, additional ancillary studies, continued conservative care or surgery referral as determined by team
  • Category IV: neoplastic
    • Neoplastic: benign
      • Cytological specimen sufficiently cellular and representative (with or without the context of clinical, imaging and ancillary studies) to be diagnostic of a benign neoplasm
      • Entities include:
        • Serous cystadenoma (most common)
        • Lymphangioma
        • Cystic teratoma
        • Schwannoma
      • Average ROM: 20.2%
      • Management: conservative unless irretractable symptoms, large sized lesions at risk for rupture (> 4 cm serous cystadenomas) or increased risk of recurrence (lymphangiomas)
    • Neoplastic: other
      • Neoplasm that is either premalignant or low grade malignant
      • Does not define the neoplasm as benign or malignant
      • Entities include:
        • Premalignant
          • Intraductal papillary mucinous neoplasm (IPMN) with low and high grade dysplasia
          • Intraductal papillary neoplasm of the bile duct (IPNB) with low and high grade dysplasia
          • Mucinous cystic neoplasm (MCN) with low grade dysplasia
          • Note that cases with prominent high grade dysplasia may often end up in the suspicious for malignancy category
        • Low grade malignant
          • Pancreatic neuroendocrine tumor (PanNET)
            • Infers well differentiated neoplasm > 0.5 cm unless otherwise classified
          • Solid pseudopapillary neoplasm (SPN)
            • If FNA is suggestive but not diagnostic, categorize as atypical rather than suspicious
          • Gastrointestinal stromal tumor (GIST)
          • Extra-adrenal paraganglioma
          • Novel reports of preoperatively diagnosing pancreatic solitary fibrous tumor by FNA (Cytopathology 2022;33:222, J Am Soc Cytopathol 2020;9:272)
        • Average ROM: 37.5%
        • Management: conservative, especially if lesion is small (PanNET < 2 cm)
  • Category V: suspicious for malignancy
    • Some (but an insufficient number) of the typical features of a specific neoplasm are present, mainly pancreatic adenocarcinoma
    • Significant cellular or architectural atypia but insufficient qualitative / quantitative findings for conclusive diagnosis, insufficient tissue for confirmative ancillary testing or rare cells with multiple major criteria, as listed below:
      • Significant nuclear enlargement, nuclear membrane irregularities, course chromatin pattern, distinct nucleoli, increased N:C ratio, anisonucleosis (3:1 to 4:1), sometimes mucinous metaplasia
      • Loss of cellular and architectural polarity
    • Entities include:
      • Pancreatic adenocarcinoma (most common)
      • Solid cellular smear patterns suggestive of:
        • PanNET, acinar cell carcinoma, pancreatoblastoma, solid pseudopapillary neoplasm (SPN)
      • Cyst aspirates with solid mural nodule or cyst wall mass
      • Lymphoma
      • Metastases
      • High grade biliary intraepithelial neoplasia (BilIN) sampled by brushing (not high grade PanIN)
    • Average ROM: 92.1%
    • Management: reassess or repeat sampling; perform ancillary testing (may refer for surgery if positive FISH or loss of SMAD4 staining); consult experts
  • Category VI: positive for malignancy
    • Neoplasms that unequivocally display malignant cytologic characteristics
      • Pancreatic ductal adenocarcinoma (PDAC) (most common):
        • Well differentiated
          • Difficult to diagnose; often classified as suspicious unless clearly malignant
        • Moderately and poorly differentiated:
          • Nuclear overlap and molding, marked loss of nuclear polarity, anisonucleosis > 4:1, disorganization (drunken honeycomb), macronucleoli, bizarre nuclei, nuclear hyperchromasia, elevated N:C ratio > 0.6, irregular chromatin distribution, lack of glandular differentiation, presence of cell balls, papillary fragments, cell in cell arrangements, tumor diasthesis, 3 dimensional fragments, cytoplasmic mucin vacuoles, background necrosis and mitoses
    • Entities include:
      • Pancreatic ductal adenocarcinoma and its variants
      • Cholangiocarcinoma
      • Acinar cell carcinoma
      • High grade neuroendocrine carcinoma (small cell and large cell)
      • Pancreatoblastoma
      • Lymphomas
      • Sarcomas
      • Metastases to the pancreas
    • Average ROM: 99.6%
    • Management: surgical resection; may also consider neoadjuvant therapy or clinical trials if lesions are unresectable
Diagrams / tables

Table 1: Papanicolaou reporting system for pancreaticobiliary cytology
Diagnostic categories Average risk of malignancy Examples of entities Selected ancillary testing Management


I. Nondiagnostic

23.1% 		  •   Cellular artifact, obscuring hemorrhage or necrosis
  •   Pure GI contamination
  •   Acellular cyst aspirate with no evidence of mucinous
    etiology
  •   Benign pancreatic parenchyma with clearly defined mass
    on imaging 		Cyst fluid analysis: CEA and amylase (no mucinous etiology = lack of mucin, lack of elevated CEA, lack of KRAS or GNAS mutations)

Reassess / repeat


II. Negative

8.2% 		  •   Pancreatitis
  •   Pseudocyst
  •   Lymphoepithelial cyst
  •   Splenule / accessory spleen
  •   Benign pancreatic parenchyma with no mass on imaging
Pseudocyst: high amylase + low CEA

Conservative

III. Atypical 		46.8% (range:
28 - 100) 		  •   Ductal cells with indeterminate atypia (reactive versus low
    grade dysplasia, versus scant lesional tissue)
  •   Abundant intracytoplasmic mucin in the epithelium 		Cyst fluid analysis: CEA and amylase Conservative, repeat or surgery

IV. Neoplastic: benign
20.2% 		  •   Serous cystadenoma (SCA)
  •   Lymphangioma
  •   Cystic teratoma
  •   Schwannoma 		SCA: low amylase + low CEA, VHL mutation, positive inhibin staining
Conservative




IV. Neoplastic: other



37.5% 		  •   GIST
  •   Extra-adrenal paraganglioma
  •   Pancreatic solitary fibrous tumor
Premalignant
  •   IPMN with dysplasia
  •   IPNB
  •   MCN with dysplasia
Low grade malignant
  •   PanNET
  •   Solid pseudopapillary neoplasm (SPN) 		Solitary fibrous tumor: STAT6 mutation

Intraductal papillary mucinous neoplasm: KRAS, RNF43, GNAS (specific), TP53, SMAD4 mutations

Solid pseudopapillary neoplasm: CTNNB1 (beta catenin) mutation


Surgery with an option for conservative management in select scenarios




V. Suspicious



92.1% 		  •   Pancreatic ductal adenocarcinoma (PDAC)
  •   PanNET
  •   Acinar cell carcinoma
  •   Pancreatoblastoma
  •   Solid pseudopapillary neoplasm
  •   Cyst aspirate with solid mural nodule or cyst wall mass
  •   Lymphoma
  •   Metastases
  •   High grade BilIN

Immunocytochemistry, FISH molecular analysis

Cyst fluid analysis: CEA and amylase



Surgery





VI. Positive




99.6%
  •   PDAC and variants
  •   Cholangiocarcinoma
  •   Acinar cell carcinoma
  •   Small and large cell neuroendocrine carcinoma
  •   Pancreatoblastoma
  •   Lymphomas
  •   Sarcomas
  •   Metastases to the pancreas 		Immunocytochemistry patterns in malignancy:
  •   Positive: S100P, IMP3,
    MUC4, mesothelin
  •   Negative: pVHL, CD10,
    clusterin beta, SMAD4
FISH significantly improves diagnostic sensitivity of adenocarcinoma (copy number abnormalities in CEP3, CEP7, CEP17 and of band 9p21)


Surgery or neoadjuvant therapy / clinical trials

Laboratory
  • Pancreaticobiliary strictures (Diagn Cytopathol 2014;42:351)
    • Fluorescence in situ hybridization (FISH)
      • DNA probe set for biliary brush specimens; outperforms routine cytology in sensitivity, thus is the preferred complement
        • Malignancy: chromosomal copy number abnormalities in CEP3, CEP7, CEP17 and of band 9p21 (CEP = centromere enumeration probe)
      • Successful for evaluating negative, inconclusive and malignant specimens
    • Immunocytochemistry
      • Marker patterns frequently observed in malignancy: S100P+, pVHL-, IMP3+, CD10-, MUC4+, mesothelin+, clusterin beta-
    • KRAS mutational analysis
      • Sensitive for invasive carcinomas and PDAC but not specific
        • Abnormalities also observed in low grade dysplasias and chronic pancreatitis
      • Shown utility in distinguishing benign from malignant in atypical specimens
      • Not supported as useful in diagnosing solid pancreatic masses and bile duct strictures
  • Pancreatic cystic lesions
    • Histochemical stains
      • Positive staining of mucin (mucicarmine and Alcian blue / PAS)
      • Diagnostically useful to identify mucinous lesions
    • Biochemical tests
      • Amylase and carcinoembryonic antigen (CEA) levels help diagnose:
        • Pseudocysts (high amylase in the 1,000s U/L, low CEA)
        • Serous cystadenomas (low amylase < 1,000 U/L, low CEA)
        • Mucinous cysts (CEA > 192 ng/mL)
        • Cyst fluid CEA alone reliably distinguishes mucinous from nonmucinous lesions (Diagn Cytopathol 2014;42:351)
      • CA125 and CA19-9 generally not useful for diagnosis
      • MUC2, MUC4 and MUC7 useful in recognizing dysplasia and malignancy in cystic neoplasms
    • DNA analysis
      • Aneuploid and tetraploid results support malignancy
      • Elevated cyst fluid DNA supports malignancy
      • No significantly improved diagnostic accuracy over routine cytology
    • Molecular tests
      • Mutations: supported diagnosis
        • KRAS, GNAS, RNF43: IPMN and MCN (GNAS absent in MCN)
        • TP53, SMAD4, CTTNB1, mTOR genes: advanced neoplasia (high grade dysplasia or carcinoma)
        • VHL: serous cystadenomas
        • CTNNB1 (beta catenin): solid pseudopapillary neoplasms
  • Solid pancreatic neoplasms
    • Immunohistochemical tests
      • Adenocarcinoma: DPC4 / SMAD4-
      • PanNET: chromogranin+, synaptophysin+, INSM1+, CD56+, neuron specific enolase+, CK8/18+
      • Acinar cell carcinoma: BCL10+, amylase+, trypsin+, chymotrypsin+, lipase+, CK7+
      • Solid pseudopapillary neoplasm: nuclear beta catenin+, alpha-1 antitrypsin+, CD10+, SOX11+, synaptophysin+, chromogranin-, trypsin- (Cancer Cytopathol 2017;125:831)
      • Pancreatic and biliary tract lymphoma: will be dependent on the type of lymphoma
    • Molecular analysis
      • Adenocarcinoma
        • KRAS mutation not used due to low specificity for malignancy
        • p16 / CDKN2A, TP53 and SMAD4 inactivation
        • FISH significantly improves diagnostic sensitivity; the most reliable adjunct test for confirmation for biliary tract brushing
          • Copy number abnormalities in CEP3, CEP7, CEP17 and of 9p21
        • MicroRNA and loss of heterozygosity: clinical use and importance to be determined
      • PanNET
        • Loss of heterozygosity: malignant associations but clinical importance to be determined
        • ATRX FISH performed by some labs along with DAXX IHC to identify patients with a poor prognosis (Cancer Cytopathol 2017;125:544)
      • Acinar cell carcinoma
        • Associated with losses of 11p; diagnostic significance unclear
      • Solid pseudopapillary neoplasm
        • Somatic point mutation in exon 3 of beta catenin
Case reports
Cytology images

Contributed by Derek Allison, M.D.

Duodenal contaminant only

GI contaminant only

Benign pancreatic parenchyma

Pancreatic splenule

Pancreatic splenule (CD8+)

Pancreatic splenule (CD45+)


Lymphoepithelial cyst

Clean mucin

IPMN with cytologic atypia

Reactive atypia; chronic pancreatitis

Biliary brush stricture


Serous cystadenoma

Serous cystadenoma: inhibin

Well differentiated
NET, WHO grade 1

 

Solid pseudopapillary neoplasm


Mucinous cystic neoplasm

Suspicious for pancreatic adenocarcinoma

Pancreatic ductal adenocarcinoma

Well differentiated pancreatic adenocarcinoma

PDAC by biliary brush

Board review style question #1


According to the Papanicolaou reporting system for pancreaticobiliary cytology, what is the most likely category of this adequate pancreatic FNA biopsy specimen?

  1. Negative for malignancy
  2. Neoplastic: benign
  3. Neoplastic: other
  4. Suspicious for malignancy
Board review style answer #1
C. Neoplastic: other. Solid pseudopapillary neoplasm of the pancreas, characterized by small, discohesive cells surrounding branching capillaries, is considered a low grade malignant entity. The neoplastic: other category includes neoplasms that are either premalignant or low grade malignant.

Comment Here

Reference: Pancreas - Papanicolaou system
Board review style question #2


Which ancillary test result supports the FNA diagnosis of this pancreatic body mass?

  1. Copy number abnormalities in CEP4, CEP10 and CEP14
  2. Negative DPC4 / SMAD4 by IHC
  3. Nuclear beta catenin
  4. VHL mutation
Board review style answer #2
B. Negative DPC4 / SMAD4 by IHC. Pancreatic adenocarcinoma is supported by DPC4 / SMAD4 loss. The presence of copy number abnormalities in CEP3, CEP7, CEP17 (note the correct chromosomes) and of band 9p21 are characteristic of pancreatic and biliary malignancies. Serous cystadenoma is associated with mutated VHL. Nuclear beta catenin supports a diagnosis of solid pseudopapillary neoplasm.

Comment Here

Reference: Pancreas - Papanicolaou system
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