The Milan System for Reporting Salivary Gland Cytopathology and Updates
image: (a) Non-diagnostic: FNA of a right parotid gland “lesion” showed only scant salivary gland parenchymal cells (Papanicolaou stain). (b) Non-neoplastic: FNA of a right parotid gland showed abundant neutrophils and histiocytes, consistent with abscess (Diff-quik stain). (c) AUS: FNA of a right parotid gland lesion showed single large atypical cells in the background of lymphoid tissue (Papanicolaou stain). Follow-up surgical resection revealed low-grade Non-Hodgkin B-cell lymphoma. (d) Neoplastic-benign: Classic cytomorphologic features of PA showed by Papanicolaou stain. (e) SUMP: A cellular specimen with basaloid appearing cells diagnosed as SUMP (Diff-Quik stain). Follow-up surgical specimen revealed basal cell adenoma. (f) SM: Clusters of epithelial cells including scattered mucin-filled cells, suspicious for neoplasm. Overall cellularity was low. Follow-up surgical specimen showed low-grade mucoepidermoid carcinoma (Papanicolaou stain).
Credit: He Wang, Xi Wang
Salivary gland neoplasms (SGNs) represent a diverse and complex group of tumors with varying histological characteristics. The introduction of fine-needle aspiration (FNA) has been instrumental in the preoperative assessment of SGNs due to its minimal invasiveness and cost-effectiveness. However, the absence of a standardized reporting system led to inconsistencies in diagnoses and patient management. This gap was addressed by the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC), established in 2018. The MSRSGC provides a uniform framework for categorizing salivary gland lesions, improving diagnostic accuracy and facilitating better communication among healthcare providers globally.
The Reporting System
The MSRSGC categorizes salivary gland lesions into six diagnostic groups, each with defined criteria, risk of malignancy (ROM), and clinical management recommendations.
- Non-diagnostic (ND): This category includes cases with insufficient cellular material (<60 lesional cells), preparation artifacts, or benign salivary gland elements without sufficient evidence of a neoplastic process. The average ROM for ND cases is approximately 25%, and a repeat FNA is recommended for conclusive diagnosis.
- Non-neoplastic (NN): These are benign lesions, including reactive lymphoid hyperplasia and granulomatous sialadenitis, which show no evidence of neoplastic processes. The ROM for NN lesions is about 10%, and clinical follow-up is advised.
- Atypia of Undetermined Significance (AUS): AUS includes cases where cytological features are indeterminate between non-neoplastic and neoplastic. This category captures a spectrum of indeterminate findings that require further investigation, often through repeat FNA or other diagnostic procedures. The ROM for AUS is approximately 20%.
- Neoplasm: Benign: This category includes benign neoplasms such as pleomorphic adenoma and Warthin tumor. The ROM is less than 5%, and clinical management usually involves conservative surgical excision or observation.
- Neoplasm: Salivary Gland Neoplasm of Uncertain Malignant Potential (SUMP): Cases in this category have cytomorphologic features suggestive of a neoplasm but lack definitive characteristics to rule out malignancy. The ROM for SUMP is about 35%, necessitating nerve-sparing surgical resection.
- Suspicious for Malignancy (SM) and Malignant: These categories represent lesions with cytological features highly suggestive of or diagnostic for malignancy, respectively. The ROM for SM is significantly high, warranting immediate and aggressive clinical intervention.
Perspectives and Updates
Since its inception, the MSRSGC has been widely adopted and validated, significantly impacting the diagnosis and management of SGNs. However, feedback and new insights have prompted considerations for updates. Key areas for improvement include:
- Clarifying the Non-Diagnostic Category: The current criterion for the ND category, which is based on the presence of fewer than 60 lesional cells, lacks robust validation. Additionally, the ROM for ND lesions appears to be higher than expected, suggesting a need for clearer guidelines.
- Sub-classification within Categories: Given the variability in ROM within the same diagnostic category, there is a potential benefit in further sub-classifying these groups to provide more precise prognostic information and management.
- Incorporation of Molecular Markers: The rapid advancement in molecular diagnostics, including next-generation immunohistochemistry and gene rearrangement detection, presents an opportunity to enhance the diagnostic accuracy of the MSRSGC. Integrating these tools into routine practice could provide deeper insights into the molecular underpinnings of SGNs and refine diagnostic categories.
Conclusions
The MSRSGC has revolutionized the approach to diagnosing and managing salivary gland neoplasms by providing a structured and standardized reporting system. As our understanding of these neoplasms evolves, ongoing updates and refinements to the MSRSGC are crucial to maintaining its relevance and effectiveness in clinical practice. Incorporating new molecular diagnostic techniques and addressing existing challenges will further enhance its utility, ultimately leading to improved patient outcomes in the diagnosis and management of salivary gland lesions.
Full text
https://www.xiahepublishing.com/2771-165X/JCTP-2023-00011
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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