Fine-needle aspiration cytology of myoepithelial carcinoma of salivary gland: Diagnostic challenge to cytopathologist

Pitfalls in Diagnosis of Myoepithelial Carcinoma of Salivary Glands: A Study of 3 Cases with Cytologic-histologic Correlation and Molecular Analysis

CONTEXT

Myoepithelial carcinoma (MECA) represents < 1% percent of salivary gland (SG) tumors with a mean age of 55 years. These tumors can arise de novo or in association with pre-existing pleomorphic Adenoma (PA). The cytologic features of MECA overlap with other SG neoplasms including the more common benign entities like PA and myoepithelioma and can pose a diagnostic challenge.

DESIGN

A database search for MECA was performed spanning 10 years. 3 cases qualified with available cyto-histologic correlation. All were morphologically MECA with one case diagnosed as MECA ex-PA. The cases were subjected to a comprehensive immunohistochemical and molecular evaluation (Case#1 has been previously reported and published in head and neck pathology in 2021).

RESULTS

A comparative analysis of these cases is presented in Table 1. All three cases were initially diagnosed as PA on cytology. On review of cytology slides, presence of metachromatic stromal fragments and bland myoepithelial cells was found to be the most common diagnostic pitfall. S100 was positive in all cases while myosin, p63, and GFAP were variably positive. Molecular analysis revealed novel, previously undescribed mutations in the three cases. Additionally, two of three cases expressed PD-L1, suggesting a role for immunotherapy in treatment.

CONCLUSIONS

Cytomorphology of MECA is poorly described in literature and can pose a diagnostic challenge due to overlapping features with salivary gland benign neoplasms. A conclusive diagnosis on cytology is often not possible. However, a high cellularity, predominant oncocytoid/ myoepithelial cell population on smears and cell block, along with a strong clinical and radiologic suspicion for malignant salivary gland tumor, should alert the cytopathologist and help avoid an erroneous benign diagnosis on cytology.

Cytopathology of salivary gland myoepithelial carcinoma: A study of 13 cases and review of the literature

INTRODUCTION

Myoepithelial carcinoma (MECA) is an infrequently recognized salivary gland (SG) neoplasm that commonly develops within a preexisting pleomorphic adenoma (MECA ex PA). Fine-needle aspiration (FNA) biopsy reports of this neoplasm are largely restricted to small series and single case reports.

METHODS

Our cytopathology files were searched for examples of SG MECA/MECA ex PA having confirmatory histopathologic verification. Conventional FNA biopsy smears were performed, and exfoliative specimens processed using standard techniques.

RESULTS

Thirteen cases from 9 patients (M:F = 3.5:1; age range: 36 to 95 years, mean age = 60 years) met inclusion criteria. FNA biopsy sites included parotid gland (4), trunk (2), scalp (2), and neck (2). Exfoliative specimens included pleural fluid (1), bronchial brushing (1), and bronchoalveolar lavage (1). Most cases were metastatic deposits (8; 62%), 4 were primary neoplasms, and 1 a local recurrence. FNA diagnoses were MECA ex PA (6; 46%), myoepithelial neoplasm (2), PA (2), basaloid neoplasm (1), atypical myoepithelial cells (1), and myxoma (1). Ancillary testing in 2 cases showed positive staining for myoepithelial markers. Cytologic features were that of a low-grade neoplasm composed principally of epithelioid/polygonal cells exhibiting minimal if any cytologic atypia. Myxoid and chondromyxoid stroma was often the dominant feature in MECA ex PA aspirates.

CONCLUSION

In the primary setting, a cytologic diagnosis of MECA/MECA ex PA is extremely challenging if at all possible. Due to overwhelming amounts of stroma, the diagnosis may be challenging in some cases of metastatic MECA ex PA.

Salivary gland lesions: diagnostic reliability and challenges of fine needle aspiration cytology

Fine needle aspiration cytology (FNAC) is a valuable, safe and widely used method for preoperative diagnosis of salivary gland lesions. The diagnostic accuracy of FNAC is dependent on the quality and yield of the aspirate, as well as the experience and knowledge of the cytopathologist. 247 cases of FNAC of salivary gland lesions were performed in our 4-year retrospective study. FNAC diagnoses were divided into non-neoplastic lesions, benign and malignant neoplasms. Histopathologic confirmation was done in 101 cases. The cases with discrepancies between the FNAC and histopathologic results were reviewed to establish possible reasons for discordance. The measures of diagnostic validity of FNAC in diagnosing non-neoplastic, benign and malignant lesions were evaluated. Of the 247 FNAC samples, 135 cases were diagnosed as benign neoplasms, 15 as malignant neoplasms, and 97 as non-neoplastic lesions. Out of the 101 cases with histopathologic confirmation, discordant results between cytologic and histopathologic diagnosis were observed in 15 cases. Our study showed no false positive and 4 false negative results for cancer. Cystic presentation of a lesion was a common reason for diagnostic pitfall. Sensitivity of FNAC in various types of salivary gland lesions ranged from 75%-100%, specificity 81-100%, diagnostic accuracy 85-96%, PPV 31-100% and NPV 60-96%. FNAC is a highly sensitive and specific method for diagnosis of most salivary gland lesions. Despite the fact that histopathology remains the gold standard, preoperative FNAC should be considered for preliminary investigation. Due to the diagnostic pitfalls, FNAC should be used in conjunction with clinical information, physical examination, and radiologic findings to reach the right diagnosis.

Assessing the diagnostic accuracy for pleomorphic adenoma and Warthin tumor by employing the Milan System for Reporting Salivary Gland Cytopathology: An international, multi-institutional study

BACKGROUND

The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) has established distinct diagnostic categories for reporting cytopathological findings, and each is associated with a defined risk of malignancy (ROM). However, the ROM is applied at the overall category level and is not specific for particular morphological entities within a category. Here, the diagnostic performance of the MSRSGC for pleomorphic adenoma (PA) and Warthin tumor (WT) is reported.

METHODS

The pathology archives of 11 institutions from 4 countries were retrospectively searched to identify all salivary gland fine-needle aspiration (FNA) biopsies with a differential or definitive diagnosis of PA or WT and all resection specimens with a diagnosis of PA or WT; only paired cases were included. All FNA diagnoses were retrospectively classified according to the MSRSGC.

RESULTS

A total of 1250 cases met the inclusion criteria, and they included 898 PA cases and 352 WT cases. The ROM in the benign neoplasm category was 3.0% and 1.3% for cases with a differential or definitive diagnosis of PA and WT, respectively. The ROM in the salivary gland neoplasm with uncertain malignant potential (SUMP) category was 2.7% and 18.8% for PA and WT, respectively (P = .0277). The diagnostic accuracy for PA and WT was 95.1% and 96.1%, respectively.

CONCLUSIONS

The diagnostic accuracy for PA and WT on FNA is high. Furthermore, these findings highlight the difference in the ROMs associated with 2 specific differential diagnoses in the SUMP category: basaloid neoplasms and oncocytoid neoplasms.

Myoepithelial carcinoma of the parotid gland: A case of adequate fine-needle aspiration cytology specimens rendering a conclusive diagnosis possible

An 80-year-old male presented with a history of a hard right parotid mass that had gradually increased in size, with subsequent facial paralysis. A fine-needle aspiration biopsy was performed. The cytologic specimens contained a substantial number of sheet-like clusters or small groups of a mixture of plasmacytoid, oval to spindled, or large epithelioid cells having hyperchromatic pleomorphic nuclei, abundant cytoplasm with occasional inclusion body-like materials, and prominent nucleoli, in a relatively clear background. We first interpreted it as a carcinoma, suggestive of myoepithelial differentiation. Radical parotidectomy was performed, and a gross examination of the neoplasm revealed a non-capsulated and ill-defined tumor lesion, with a grayish or yellowish cut surface, associated with fat invasion. On a microscopic examination, the tumor was predominantly composed of the solid proliferation of atypical cells including a mixture of oval to spindled, plasmacytoid, or epithelioid cells, often arranged in a trabecular and reticular growth pattern with patchy eosinophilic hyalinized stroma. Immunohistochemistry showed that the carcinoma cells were specifically positive for p63, cytokeratins, and vimentin. Finally, electron microscopy demonstrated that their phenotype was consistent with a myoepithelial origin containing many bundles of variably thin actin filaments. Therefore, we finally made a diagnosis of myoepithelial carcinoma, defined as the malignant counterpart of benign myoepithelioma. We should be aware that owing to its characteristic cytological features, cytopathologists may be able to make a correct diagnosis of myoepithelial carcinoma, based on multiple and adequate samplings.

The value of fine needle aspiration cytology in the clinical management of rare salivary gland tumors

Salivary gland tumors are relatively rare neoplasms, mostly located in the parotid gland, and few are malignant. Preoperative evaluation of salivary gland tumors includes fine needle aspiration cytology (FNAC).

Myoepithelial carcinoma of the parotid: a rare tumour that may provide diagnostic difficulty

This report presents the case of a 57-year-old man with a 6-week history of a slowly enlarging lump in the right parotid gland. Initial ultrasound investigation confirmed a 3 cm solid mass located within the superficial lobe of the right parotid gland. Sonographically, the mass demonstrated possible malignant features with internal heterogeneity of architecture and some loss of marginal clarity. Ultrasound-guided core biopsy (USCB) of the mass reported a mixed neoplasm with epithelial and myoepithelial appearances consistent with likely benign adenoma or myoepithelioma. A right superficial parotidectomy was subsequently performed. Histological and immunohistochemical analysis of the excised specimen showed a myoepithelial carcinoma. Postoperative CT and MR staging scans did not show evidence of metastases and no further treatment was given following discussion of the case at the regional speciality multidisciplinary meeting. This case illustrates the clinical and pathological features of this rare salivary gland tumour, but also discusses the diagnostic difficulties that may be encountered preoperatively.