Salivary gland FNA: New markers and new opportunities for improved diagnosis

Update on Salivary Gland Fine-Needle Aspiration and the Milan System for Reporting Salivary Gland Cytopathology

CONTEXT.—

Fine-needle aspiration (FNA) is a well-established procedure for the diagnosis and management of salivary gland lesions, despite challenges imposed by salivary gland tumor diversity, complexity, and cytomorphologic overlap. Until recently, the reporting of salivary gland FNA specimens was inconsistent among different institutions throughout the world, leading to diagnostic confusion among pathologists and clinicians. In 2015, an international group of pathologists initiated the development of an evidence-based tiered classification system for reporting salivary gland FNA specimens, the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC). The MSRSGC consists of 6 diagnostic categories, which incorporate the morphologic heterogeneity and overlap among various nonneoplastic, benign, and malignant lesions of the salivary glands. In addition, each MSRSGC diagnostic category is associated with a risk of malignancy and management recommendations.

OBJECTIVE.—

To review the current status of salivary gland FNA, core needle biopsies, ancillary studies, and the beneficial role of the MSRSGC in providing a framework for reporting salivary gland lesions and guiding clinical management.

DATA SOURCES.—

Literature review and personal institutional experience.

CONCLUSIONS.—

The main goal of the MSRSGC is to improve communication between cytopathologists and treating clinicians, while also facilitating cytologic-histologic correlation, quality improvement, and research. Since its implementation, the MSRSGC has gained international acceptance as a tool to improve reporting standards and consistency in this complex diagnostic area, and it has been endorsed by the 2021 American Society of Clinical Oncology management guidelines for salivary gland cancer. The large amount of data from published studies using MSRSGC served as a basis for the recent update of the MSRSGC.

Salivary Gland Fine-Needle Aspiration: The Current and Future Landscape

Fine-needle aspiration represents a valid tool for the diagnosis/management of salivary gland lesions. The past years assessed the lack of uniform diagnostic reports for salivary cytopathology leading to interpretative issues. In 2015, an international group of cytopathologists developed an evidence-based tiered classification system for reporting salivary gland fine-needle aspiration (FNA) specimens, the "Milan System for Reporting Salivary Gland Cytopathology" (MSRSGC). The present landscape of salivary cytology is represented by the growing adoption of the MSRSGC and the assessment of its diagnostic role. The future landscape is characterized by the increasing role of ancillary techniques for diagnostic and prognostic purposes.

Is molecular testing of salivary gland FNA specimens ready for prime time?

With improvements in the molecular characterization of salivary gland neoplasms, fine‐needle aspiration specimens, including smears and cell blocks, are amenable to molecular testing for defining alterations, providing a specific diagnosis in many cases, and guiding management in a preoperative setting. Molecular testing can be particularly beneficial and complementary when used within the framework of the Milan system, as the results can further refine the risk of malignancy.

Molecular testing in salivary gland cytopathology: A practical overview in conjunction with the Milan system

Recently, significant advances in the molecular characterization of salivary gland neoplasms have facilitated the classification and diagnosis of specific diagnostic entities. In the highly challenging diagnostic scenario of salivary malignancies, molecular testing is increasingly being adopted in routine practice to refine the cytological diagnosis of salivary lesions. Here, we reviewed the most recent evidence in the field of salivary glands molecular cytopathology.

Second edition of the Milan System for Reporting Salivary Gland Cytopathology: Refining the role of salivary gland FNA

The use of standardised reporting systems for non-gynaecologic cytopathology has made enormous gains in popularity during the past decade, including for thyroid fine-needle aspiration, urine cytology, serous effusions, pancreas, lymph nodes, lung and more. In February 2018, the first edition of the Atlas of the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) was published. The MSRSGC defines six diagnostic fine-needle aspiration categories encompassing the spectrum of non-neoplastic, benign and malignant lesions of the salivary glands. The goal of the MSRSGC is to combine each diagnostic category with a defined risk of malignancy and a specific clinical and/or surgical management algorithm. Since its initial publication in 2018, more than 200 studies and commentaries have been published, confirming the role of the MSRSGC. The second edition of the MSRSGC, published in July 2023, includes refined risks of malignancy based on systematic reviews and meta-analyses, a new chapter summarising the use of salivary gland imaging, new advances in ancillary testing and updates in nomenclature.

Second edition of the Milan System for Reporting Salivary Gland Cytopathology: Refining the role of salivary gland FNA

The use of standardized reporting systems for nongynecologic cytopathology has made enormous gains in popularity during the past decade, including for thyroid fine-needle aspiration, urine cytology, serous effusions, pancreas, lymph nodes, lung, and more. In February 2018, the first edition Atlas of the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) was published. The MSRSGC defines six diagnostic fine-needle aspiration categories encompassing the spectrum of Non-Neoplastic, benign, and malignant lesions of the salivary glands. The goal of the MSRSGC is to combine each diagnostic category with a defined risk of malignancy and a specific clinical and/or surgical management algorithm. Since its initial publication in 2018, more than 200 studies and commentaries have been published confirming the role of the MSRSGC. The second edition of the MSRSGC, published in July 2023, includes refined risks of malignancy based on systematic reviews and meta-analyses, a new chapter summarizing the use of salivary gland imaging, new advances in ancillary testing, and updates in nomenclature. CONCISE SENTENCE: The second edition of the Milan System for Reporting Salivary Gland Cytopathology, published in July 2023, includes refined risks of malignancy based on systematic reviews and meta-analyses, a new chapter summarizing the use of salivary gland imaging, new advances in ancillary testing, updates in nomenclature, and a guide to the practical application of the latest ancillary markers for the diagnosis of selected salivary gland fine-needle aspiration cases.

Second edition of the Milan System for Reporting Salivary Gland Cytopathology: Refining the role of salivary gland FNA

The use of standardized reporting systems for non-gynecologic cytopathology has made enormous gains in popularity during the past decade, including for thyroid fine-needle aspiration, urine cytology, serous effusions, pancreas, lymph nodes, lung, and more. In February 2018, the first edition Atlas of the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) was published. The MSRSGC defines six diagnostic fine-needle aspiration categories encompassing the spectrum of non-neoplastic, benign, and malignant lesions of the salivary glands. The goal of the MSRSGC is to combine each diagnostic category with a defined risk of malignancy and a specific clinical and/or surgical management algorithm. Since its initial publication in 2018, more than 200 studies and commentaries have been published confirming the role of the MSRSGC. The second edition of the MSRSGC, published in July 2023, includes refined risks of malignancy based on systematic reviews and meta-analyses, a new chapter summarizing the use of salivary gland imaging, new advances in ancillary testing, and updates in nomenclature.

Don't SUMP it! Utility of PLAG1 immunocytochemistry in basaloid SUMP subcategory

BACKGROUND

Basaloid salivary gland neoplasm of uncertain malignant potential (B-SUMP) is an indeterminate diagnostic subcategory, with pleomorphic adenoma (PA) representing the most common benign neoplasm. Pleomorphic adenoma gene 1 (PLAG1) staining is frequently seen in PAs and could aid in distinguishing them from other basaloid neoplasms. The authors evaluated the utility of PLAG1 immunocytochemistry (ICC) in differentiating PAs from other basaloid neoplasms in smears and liquid-based cytology (LBC) specimens.

METHODS

In total, 45 B-SUMP cytology aspirates and corresponding surgical excision specimens were identified. PLAG1 immunostaining was performed in all aspirates and surgical excision specimens and was scored as positive (strong/diffuse), equivocal (focal/weak), or negative.

RESULTS

PLAG1 ICC was performed directly on 38 smears and seven LBC specimens. PLAG1 was positive in 29 of 45 cases (64%), whereas six of 45 (13%) were equivocal, and 10 of 45 (22%) were negative. PLAG1-positive aspirates included 26 (90%) PAs, two (7%) basal cell adenomas (BCAs), and one (3%) carcinoma ex-PA. PLAG1-equivocal aspirates included four (67%) PAs and two (33%) BCAs, whereas negative aspirates included five (50%) BCAs, four (40%) adenoid cystic carcinomas, and one (10%) metastatic adenosquamous carcinoma. The sensitivity, specificity, positive, and negative predictive values were 87%, 86%, 93%, and 75%, respectively. Diagnostic accuracy was 87%.

CONCLUSIONS

PLAG1 ICC is useful when positive (strong/diffuse) and can be reliably performed on smears and LBC specimens. PLAG1 was positive in most PAs and in a small subset of BCAs. Therefore, in the absence of atypical cytologic features, PLAG1-positive tumors could be diagnosed as benign, with a note favoring PA versus BCA. In contrast, PLAG1-negative/equivocal tumors should remain in the B-SUMP category.

The evolving landscape of salivary gland tumors

Salivary gland cancers are a rare, histologically diverse group of tumors. They range from indolent to aggressive and can cause significant morbidity and mortality. Surgical resection remains the mainstay of treatment, but radiation and systemic therapy are also critical parts of the care paradigm. Given the rarity and heterogeneity of these cancers, they are best managed in a multidisciplinary program. In this review, the authors highlight standards of care as well as exciting new research for salivary gland cancers that will strive for better patient outcomes.

Fine-Needle Aspiration Cytology for Parotid Tumors

Fine-needle aspiration (FNA) cytology is widely used in clinical practice as a simple and minimally invasive test for parotid tumors that allows for preoperative estimation of benignancy and malignancy, histological type, and malignancy grade and can be performed on an outpatient basis. In recent years, cell blocks prepared with core needle biopsy (CNB) and liquid-based cytology (LBC) have increased the reliability of immunostaining and molecular biological testing, leading to improved diagnostic accuracy. In 2018, the Milan System for Reporting Salivary Gland Cytology was introduced, but it does not include malignancy grade or histological type, so we proposed the Osaka Medical College classification as a more clinically based cell classification that includes both types of information, and we have reported on its usefulness. This review gives an overview of the history and use of FNA and describes CNB and LBC and the two classification systems.

Application of the Milan system for reporting salivary gland cytopathology using cell blocks

The Milan system for reporting salivary gland cytopathology (MSRSGC) is a novel standardized classification tool for salivary gland cytology specimens based on the use of direct smears. Formalin-fixed paraffin-embedded (FFPE) cell blocks facilitate the use of ancillary studies, leading to improved diagnostic accuracy. However, the application of the MSRSGC with only cell blocks has not been well established. Consecutive cohort of all parotid gland cytology specimens between 01/01/2018 and 30/06/2021 was performed. All cytology specimens were processed into cell blocks only. Cytologic diagnoses were classified prospectively according to the MSRSGC categories. The risk of malignancy (ROM) for each diagnostic category and the diagnostic performance were calculated. A total of 230 FNA samples from 221 patients were identified, including 47% and 78.4% with surgical or clinical follow-up, respectively. The ROMs based on surgical follow-up for the non-diagnostic, non-neoplastic, AUS, neoplasm: benign, SUMP, SFM and malignant categories were 21.4%,0%,50%,0%,30%,100% and 100%, respectively. The ROMs based on the clinical follow-up for these categories were 7.3%,0%,37.3%,0%,27.3%,100% and 100%, respectively. Following surgical excision, all Milan IVa category samples were confirmed as benign, and all Milan V and VI category samples were confirmed as malignant. This study validates the application of the MSRSGC with the sole use of FFPE cell blocks. The diagnostic accuracy of MSRSGC is high and compares favorably to other institutions using traditional cytology assessment methods. Furthermore, FNA results using this technique enabled to provide optimal patient management based on the ROM of the different Milan system categories.

Immunocytochemistry for diagnostic cytopathology-A practical guide

Cytological specimens, which are obtained by minimally invasive methods, are an excellent source of diagnostic material. Sometimes they are the only material available for diagnosis as well as for prognostic/predictive markers. When cytomorphology is not straightforward, ancillary tests may be required for a definitive diagnosis to guide clinical management. Immunocytochemistry (ICC) is the most common and practical ancillary tool used to reach a diagnosis when cytomorphology is equivocal, to differentiate entities with overlapping morphological features, and to determine the cell lineage and the site of origin of a metastatic neoplasm. Numerous immunomarkers are available, and some are expressed in multiple neoplasms. To rule out entities within a differential diagnosis, the use of more than one marker, sometimes panels, is necessary. ICC panels for diagnostic purposes should be customised based on the clinical context and cytomorphology, and the markers should be used judiciously to preserve material for additional tests for targeted therapies in the appropriate setting. This review offers a practical guide for the use of ICC for diagnostic cytopathology, covering the most commonly encountered non-hematolymphoid diagnostic scenarios in various body sites.

The effectiveness of the Milan system for risk stratification of salivary gland lesions: The 10-year cytohistopathological correlation results of salivary gland FNA cytology at a tertiary center

BACKGROUND

The Milan system reporting salivary gland cytopathology (MSRSGC) is a tiered classification scheme that is based on risk stratification. The aim of the current study was to assess the risk of malignancy (ROM) and risk of neoplasia (RON) in each of the diagnostic categories proposed by the MSRSGC.

METHODS

A retrospective analysis and categorization according to the MSRSGC was made of salivary gland fine needle aspirations (FNA) performed from January 2007 to December 2017. The FNA cytology results were correlated with subsequent histological follow-up.

RESULTS

A total of 578 FNAs were evaluated and histopathology was available for 198 cases (34.2%). The RON and ROM for individual diagnostic categories were: Non-diagnostic: 52.2% to 13%, non-neoplastic: 21.4% to 10.7%, atypia of undetermined significance: 74% to 22.2%, benign neoplasm: 100% to 1.1%, salivary gland neoplasm of uncertain malignant potential: 93.3% to 53.3%, suspicious for malignancy (SFM): 100% to 100%, and malignant: 100% to 100%. A diagnosis of 'SFM' or 'malignant' with FNA cytology carried a 100% risk for malignancy, while a diagnosis of "non-neoplastic," "benign neoplasm" reduced the probability of malignancy to 3.4%.

CONCLUSION

The MSRSGC is useful for the management of salivary gland lesions as it can successfully differentiate between benign and malignant cases. It will bring uniformity in salivary gland FNA cytology reporting across various institutions globally.

Next-generation sequencing assay in salivary gland cytology: A pilot study

BACKGROUND

Preoperative diagnosis of salivary gland tumors (SGTs) by fine-needle aspiration (FNA) cytology is challenging. Next-generation sequencing (NGS)-based assays for somatic mutations have a great advantage in that a large number of genes can be analyzed simultaneously. Although NGS may have an enormous diagnostic potential in cytology, to our knowledge, the significance of NGS in SGT cytology remains to be clarified.

METHODS

In this pilot study, we retrospectively examined 32 frozen SGT samples obtained at surgery (14 malignant and 18 benign). After the stored frozen tumor tissues were thawed, aspirate samples were obtained using 22-gauge needles and subjected to smear tumor samples and to DNA extraction for an NGS assay employing the Illumina AmpliSeq Cancer Hotspot Panel v2. The results were correlated to preoperative cytological diagnosis.

RESULTS

The preoperative diagnoses obtained by FNA cytology included 23 negative lesions (no malignancy in 6 and benign tumor in 17) and nine positive lesions (suspicious for malignancy in 4 and malignancy in five), providing a sensitivity and a specificity of 9/14 (64%) and 18/18 (100%), respectively. The NGS assay detected somatic mutations in 10/14 malignant and 1/18 benign SGT cases, providing a sensitivity and a specificity of 71% and 94%, respectively.

CONCLUSION

The NGS assay may be helpful for detecting the malignant potential in SGT cases and can be used as an ancillary test for SGT cytology.

A retrospective cytohistological correlation of fine-needle aspiration cytology with classification by the Milan System for Reporting Salivary Gland Cytopathology

Background

Before publication of the new classification system named the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) in 2018, there was no standard classification for salivary gland lesions obtained by fine-needle aspiration (FNA). We therefore aimed to evaluate the diagnostic utility of this system by retrospectively reviewing FNA samples using the MSRSGC and to determine their risk of developing into neoplasms and becoming malignant.

Methods

Retrospective slide review and classification of salivary gland FNAs obtained over a 6-year period (2013–2018) at a single center were performed by two pathologists. The risks of neoplasm and malignancy for each category also were calculated.

Results

This study surveyed 374 FNAs (371 patients) performed over a six-year period and selected 148 cases that included documented surgical follow-up (39.6%). Among the surgically treated cases, the distributions of FNA categories were as follows: non-diagnostic (ND; 16.9%), non-neoplastic (NN; 2.7%), atypia of undetermined significance (AUS; 3.4%), benign (BN; 54.7%), salivary gland neoplasm of uncertain malignant potential (SUMP; 10.1%), suspicious for malignancy (SM; 6.8%), and malignant (M; 5.4%). The risk of malignancy (ROM) was 24.0% for ND, 0% for NN, 40.0% for AUS, 2.5% for BN, 46.7% for SUMP, 100% for SM, and 87.5% for M. The overall diagnostic accuracy was 95.9% (142/148 cases).

Conclusions

The newly proposed MSRSGC appears to be a reliable system for classification of salivary gland lesions according to the associated ROM.

Metastatic adenoid cystic carcinoma with high-grade transformation ("dedifferentiation") in pleural effusion and neck lymph node: A diagnostic challenge on cytology?

High-grade transformation (HGT) or "dedifferentiation" is an uncommon phenomenon among salivary gland carcinomas including adenoid cystic carcinoma (ACC), which is important to recognize because it is associated with increased tumor aggressiveness, with a high propensity for lymph node and distant metastases. ACC with HGT is histologically characterized by a distinct population of poorly differentiated cells with loss of the typical biphasic ductal and myoepithelial differentiation seen in conventional ACC, associated with pleomorphism, necrosis and increased mitotic activity. We report the cytologic features of a case of metastatic ACC-HGT in cervical lymph node and effusion, which, to the best of our knowledge, have not been described previously. When ACC presents both in atypical locations and with HGT, the danger of misdiagnosis is increased if the clinical history is lacking, incomplete or inaccurate. Since ACC-HGT are rare (and possibly underdiagnosed) and do not have a specific set of cytological and/or immunohistochemical features, it is important for practicing cytopathologists to be aware of the possibility of encountering them, especially in specimens from patients with a history of ACC, in order to render the correct diagnosis.

Salivary Gland FNA Diagnostics in a Real-Life Setting: One-Year-Experiences of the Implementation of the Milan System in a Tertiary Care Center

The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) was introduced in 2018 following other organ specific cytopathological reporting systems and it aimed at bringing a practical, evidence-based, user-friendly classification system with characterization and management algorithms. At the Department of Pathology, Fimlab Laboratories, Tampere, Finland all salivary fine needle aspirations (FNAs) have been given cytopathological diagnoses according to the MSRSGC since January 2018. Analyses of a one-year-period (January 2018–December 2018) consisted of 183 salivary FNA samples from 138 patients with correlation to histopathology in 90 cases with surgical follow-up. The MSRSGC performance in patient based analysis was as follows: accuracy was 90.9%, sensitivity was 61.5%, specificity was 100%, positive predictive value was 100%, and negative predictive value was 89.4%, respectively. Risks of malignancy (ROMs) in MSRSGC categories were: 0.0% (0/15) in non-diagnostic category, 100.0% (1/1) in non-neoplastic category biased by only one falsely-negative lymphoma case, 14.3% (1/7) in atypia of undetermined significance category, 0.0% (0/28) in benign neoplasm category, 27.3% (3/11) in neoplasm of uncertain malignant potential category, and 100% for both suspicious for malignancy (4/4) and malignancy (4/4) categories, respectively. The MSRSGC has been proven as a reliable classification system in salivary gland FNA routine diagnostics in a tertiary care center.

The risk of malignancy according to Milan reporting system of salivary gland fine-needle aspiration with Becton Dickinson SurePath liquid-based processing

BACKGROUND

Fine-needle aspiration cytology (FNAC) is a noninvasive, safe, cost-effective, diagnostic procedure for the evaluation of salivary gland lesions and the selection of patients for surgery. The aim of this study was to analyze the risk of malignancy (ROM) according to the Milan reporting system of salivary gland FNA specimens using a liquid-based cytology (LBC) technique.

METHODS

The cytological diagnosis of 459 cases between 2014 and 2017 was revised according to the Milan reporting system. The FNAC results of 129 cases with a histological diagnosis were compared with respect to the final diagnosis. The ROM for each category calculated.

RESULTS

The ROM was high in the indeterminate and malignant categories, while the ROM in the benign neoplasm category was low. Sensitivity and specificity analyzed in two different ways were 95.1% and 88.8%, 81%, and 77.7%, respectively.

CONCLUSIONS

When salivary gland lesions are evaluated together with clinical and radiological data, the LBC technique can be applied to salivary gland specimens based on the high diagnostic sensitivity and specificity in liquid-based samples reported according to the Milan system.

Salivary Gland Fine Needle Aspiration and Introduction of the Milan Reporting System

Fine needle aspiration (FNA) is a well-established procedure for the diagnosis and management of salivary gland lesions despite challenges imposed by their diversity, complexity, and cytomorphologic overlap. Until recently, the reporting of salivary gland FNA specimens was inconsistent among different institutions throughout the world, leading to diagnostic confusion among pathologists and clinicians. In 2015, an international group of pathologists initiated the development of an evidence-based tiered classification system for reporting salivary gland FNA specimens designated the "Milan System for Reporting Salivary Gland Cytopathology" (MSRSGC) that culminated with the publication of the MSRSGC Atlas in February 2018. The MSRSGC consists of 6 diagnostic categories, which incorporate the morphologic heterogeneity and overlap among various non-neoplastic, benign, and malignant lesions of the salivary glands. In addition, each diagnostic category is associated with a risk of malignancy and management recommendations. The main goal of the MSRSGC is to improve communication between cytopathologists and treating clinicians, while also facilitating cytologic-histologic correlation, sharing of data from different laboratories for quality control, and research. Herein, we review the current status of salivary gland cytology and the role of MSRSGC in providing a framework for reporting salivary gland lesions.

Risk stratification of salivary gland cytology utilizing the Milan system of classification

BACKGROUND

The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) is based on risk stratification. Our study is a retrospective review of salivary gland fine needle aspiration cytology (FNAC) with the goal of determining the risk of malignancy (ROM) in each of the categories proposed by the MSRSGC.

METHODS

FNAC of salivary gland lesions with corresponding surgical resection specimens were retrieved over a 5-year period. Metastatic tumors were excluded. BothFNAC and corresponding surgical resections were reviewed blindly and classified as per criteria published by the MSRSGC. The ROM for each of the diagnostic categories was determined and compared with the ROM published by the MSRSGC.

RESULTS

The total number of entities and ROM in 199 reviewed cases were as follows: Nondiagnostic 18 (9.2%) (ROM 0%), non-neoplastic 4(2%) (ROM 0%), atypia of undetermined significance (AUS) 12(6%) (ROM 33%), benign neoplasm 118(59.2%) (ROM 0.8%), salivary gland neoplasm of uncertain malignant potential (SUMP) 22(11%) (ROM 40.9%), suspicious for malignancy 3(1.5%) (ROM 100%), malignant 22(11%) (ROM 100%).

CONCLUSION

The ROM reported in our study was mostly concordant with ROM published by the MSRSGC. This classification is helpful for the management of categories; nondiagnostic, non-neoplastic, benign neoplasm, suspicious for malignancy and malignant. The management is not standardized for the category, salivary gland neoplasm of uncertain malignant potential, as clinical information plays an important role in planning surgical procedures at an individual basis. Further studies will need to be performed using this new classification to help define appropriate management and predict ROM more accurately.

Use of fluorescent in-situ hybridisation in salivary gland cytology: A powerful diagnostic tool

OBJECTIVE

Salivary gland cytology is challenging because it includes a diversity of lesions and a wide spectra of tumours. Recently, it has been reported that many types of salivary gland tumours have specific molecular diagnostic signatures that could be identified by fluorescent in-situ hybridisation (FISH). The aim of the present study was to demonstrate the feasibility and efficiency of FISH on routine cytological salivary gland smears.

METHODS

FISH was conducted on 37 cytological salivary gland smears from 34 patients. According to the cytological diagnosis suspected, MECT1/MAML2 gene fusion and rearrangements of PLAG1, MYB, or ETV6 were analysed. The presence and percentages of cells that had gene rearrangements were evaluated. Results were compared with the histological surgical samples, available from 26 patients.

RESULTS

The PLAG1 rearrangement was observed in 12/20 (60%) cases of pleomorphic adenoma. MECT1/MAML2 gene fusion was observed in 1:2 mucoepidermoid carcinomas but was not observed in five other tumours (two pleomorphic adenomas, one Warthin's tumour, one mammary analogue secretory carcinoma [MASC] and one cystic tumour). MYB rearrangement was observed in 4/4 adenoid cystic carcinomas. ETV6-gene splitting identified one MASC.

CONCLUSION

Overall, FISH had a specificity of 100% and a sensitivity of 66.7%. When FISH and cytological analyses were combined, the overall sensitivity was increased to 93.3%. It can thus be concluded that when the FISH analysis is positive, the extent of surgery could be determined with confidence pre-operatively without needing a diagnosis from a frozen section.

PLAG1: An Immunohistochemical Marker with Limited Utility in Separating Pleomorphic Adenoma from Other Basaloid Salivary Gland Tumors

OBJECTIVE

Fine-needle aspiration (FNA) diagnosis of salivary gland neoplasms is often challenging. Differentiating between pleomorphic adenomas (PA) and other basaloid neoplasms, especially basal cell adenoma (BCA) and adenoid cystic carcinoma (AdCC), can be difficult in cellular aspirates. PLAG1 (PA gene 1) is a proto-oncogene, which is frequently rearranged in PAs, leading to the aberrant expression of its protein. PLAG1 IHC expression has been reported to be positive in most PAs. The aim of this study was to evaluate the sensitivity and specificity of PLAG1 to differentiate PA from other basaloid neoplasms.

STUDY DESIGN

Immunohistochemical evaluation of PLAG1 was performed on 125 cases (52 FNAs and 73 surgical excisions). Nuclear staining of tumor cells was scored by the intensity and percentage of positive tumor cells. A combined score of >5 was defined as positive.

RESULTS AND CONCLUSION

The sensitivity (55%) and specificity (75%) of PLAG1 in diagnosing PA in FNAs is relatively modest thus limiting its diagnostic utility. BCAs and AdCCs showed PLAG1 false positivity, in surgical excision specimens and less so in FNAs. This may be due to limited sampling or tumor heterogeneity. Hence, PLAG1 is a modest marker for PAs in FNAs.

Usefulness of translocation-associated immunohistochemical stains in the fine-needle aspiration diagnosis of salivary gland neoplasms

BACKGROUND

Fine-needle aspiration diagnosis of pleomorphic adenoma (PA) and adenoid cystic carcinoma (ACC) is challenging due to cytologic overlap with one another and with other salivary gland tumors having prominent epithelial and myoepithelial components. Recognition of characteristic chromosomal aberrations in several salivary gland tumors, including PA and ACC, has the potential to resolve diagnostic uncertainty, but molecular diagnostics are not routinely available. To leverage these molecular alterations, the authors examined a panel of commercially available immunostains directed at commonly overexpressed proteins in translocation-associated PA (PLAG1 and HMGA2) and ACC (MYB) to assess their diagnostic usefulness.

METHODS

Immunohistochemistry was performed on cell block samples from 74 patients, including 11 ACC specimens and 31 PA specimens with antibodies to MYB, PLAG1, and HMGA2 as well as KIT (previously considered useful in the diagnosis of ACC).

RESULTS

ACCs demonstrated significantly greater staining for KIT compared with non-ACCs, while PAs had significantly greater staining for PLAG1 than non-PAs. MYB trended toward significance for ACC (P=.097) and HMGA2 trended toward significance for PA (P=.094). No ACC exhibited positive staining for PLAG1 or HMGA2. Only 12% of PAs were found to be positive for MYB or KIT. Combined positivity for MYB and KIT with negative PLAG1 and HMGA2 demonstrated a specificity and positive predictive value of 1.0 for ACC, whereas a positive PLAG1 or HMGA2 stain with negative MYB and KIT stains showed a sensitivity of 0.75, a specificity of 0.96, and a positive predictive value of 0.95 for PAs.

CONCLUSIONS

An immunohistochemical panel of MYB, KIT, PLAG1, and HMGA2 on fine-needle aspiration cell blocks is useful in distinguishing ACCs and PAs from each other and other salivary gland neoplasms. Cancer Cytopathol 2016;124:397-405. © 2016 American Cancer Society.