The World Health Organization system for reporting pancreaticobiliary cytopathology: Standardized categories and practical approaches to pancreatic lesions

Pancreaticobiliary cytopathology has emerged as a critical diagnostic tool, especially in evaluating pancreatic and bile duct lesions. Traditionally, endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) has been the preferred method for obtaining samples from pancreatic masses, while bile duct brushing via endoscopic retrograde cholangiopancreatography (ERCP) is commonly used for bile duct strictures. In 2022, the World Health Organization (WHO) introduced a seven-tiered system to standardize the reporting of pancreaticobiliary cytopathology, aiming to improve diagnostic consistency and communication between pathologists and clinicians.

The WHO Seven-Tier Reporting System

The WHO system categorizes cytopathology findings into seven diagnostic categories: non-diagnostic, benign, atypical, low-risk neoplasm, high-risk neoplasm, suspicious for malignancy, and malignant. Each category provides a framework for guiding the interpretation of cytology samples and their clinical management. This system refines and builds on the Papanicolaou Society of Cytopathology’s prior six-tier system, particularly reclassifying benign and neoplastic categories for better risk stratification.

Non-diagnostic and Benign Specimens

Samples that lack sufficient epithelial cells for a diagnosis or that are composed entirely of benign tissue with no representation of the targeted lesion are categorized as non-diagnostic. Such cases often require repeat sampling or further investigation. Benign specimens, which exhibit no malignant features, may include conditions like serous cystadenoma or chronic pancreatitis. However, misclassification is possible due to overlapping features with low-grade neoplastic lesions, which necessitates caution in clinical management.

Atypical and Low-Risk Neoplasms

The atypical category includes samples with minimal cellular atypia that cannot definitively be categorized as benign or malignant. This category often introduces diagnostic uncertainty, and the risk of malignancy (ROM) varies widely. Low-risk neoplasms, such as intraductal papillary mucinous neoplasm (IPMN) with low-grade dysplasia, are less likely to progress to malignancy. Ancillary tests, like carcinoembryonic antigen (CEA) levels, and molecular markers, such as KRAS mutations, are instrumental in differentiating low-risk neoplasms from benign or reactive changes.

High-Risk Neoplasms and Suspicious for Malignancy

High-risk neoplasms show features of severe atypia and are associated with a higher ROM. Surgical resection is often recommended for such cases, given their potential for progression to invasive malignancies. The suspicious for malignancy category is used when cytological features are suggestive but not definitive for cancer, often prompting additional diagnostic procedures or surgical intervention.

Malignant Lesions

The malignant category includes samples with unequivocal cytopathological features of malignancy, such as pancreatic ductal adenocarcinoma or cholangiocarcinoma. Accurate diagnosis in this category is crucial for determining the appropriate therapeutic course, which may include surgery, chemotherapy, or radiation therapy.

Use of Ancillary Tests

Ancillary testing, including molecular analysis and immunocytochemistry, plays a pivotal role in improving the accuracy of cytopathological diagnoses. For example, the detection of KRAS or GNAS mutations can help confirm the presence of mucinous neoplasms, while immunostains like trypsin and chromogranin assist in distinguishing acinar cell carcinoma and neuroendocrine tumors. This multimodal approach enhances diagnostic precision, especially in challenging or borderline cases.

Conclusions

The introduction of the WHO standardized reporting system for pancreaticobiliary cytopathology marks a significant step forward in achieving consistent and reliable diagnoses. The system not only aids pathologists in categorizing lesions based on cytological features but also supports clinical teams in making informed decisions regarding patient management. Ancillary testing further augments the diagnostic process, particularly in cases where cytology alone may be insufficient for an accurate diagnosis.

 

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https://www.xiahepublishing.com/2771-165X/JCTP-2024-00034

 

The study was recently published in the Journal of Clinical and Translational Pathology.

Journal of Clinical and Translational Pathology (JCTP) is the official scientific journal of the Chinese American Pathologists Association (CAPA). It publishes high quality peer-reviewed original research, reviews, perspectives, commentaries, and letters that are pertinent to clinical and translational pathology, including but not limited to anatomic pathology and clinical pathology. Basic scientific research on pathogenesis of diseases as well as application of pathology-related diagnostic techniques or methodologies also fit the scope of the JCTP.

 

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