Myoepithelial carcinoma ex pleomorphic adenoma of salivary glands: A problematic diagnosis

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.

"Unraveling the Tapestry": A Retrospective Exploration of Recurrent Parotid Pleomorphic Adenoma Cases

The standard surgical procedure for treating the parotid gland's recurrent pleomorphic adenoma (RPA) is parotidectomy with facial nerve preservation (FN). Treatment of RPA remains challenging since controversies occur regarding recurrence, degree of revision surgery, postoperative radiation, and difficulty in conserving the FN. A retrospective review of patient's medical records treated for benign parotid neoplasms was conducted between 2017 and 2022 to identify individuals who underwent surgery for RPA. Demographic information, surgical intervention details, pre-and postoperative facial nerve function, histopathological analysis, and recurrence rates were collected. These variables were compared in patients with single recurrent tumors versus patients with multiple recurrent tumors. Twenty-one patients met the criteria, including 13 with a first recurrence, 7 with a second recurrence, and 1 with a third recurrence. Following surgery for multiple RPA, long-term FN outcomes were significantly worse (P = 0.005). There were no observable risk factors for tumor recurrence. The interval between the initial revision surgery and subsequent ones was drastically shortened. Our study suggests that the risk of permanent facial paralysis is greater with subsequent surgical procedures. Early detection of recurrence can aid in early re-operation.

Cytopathological analysis of salivary gland cancer: REFCOR recommendations by the formal consensus method

OBJECTIVE

To determine the indications for fine-needle cytology and the modalities of frozen section pathological analysis in the management of salivary gland cancer.

MATERIAL AND METHODS

The French Network of Rare Head and Neck Tumors (REFCOR) formed a steering group who drafted a narrative review of the literature published on Medline and proposed recommendations. The level of adherence to the recommendations was then assessed by a rating group according to the formal consensus method.

RESULTS

Fine-needle cytology is recommended as part of the diagnostic work-up for a major salivary gland tumor suspicious for malignancy. Fine-needle cytology should be performed after MRI to avoid artifacts. Frozen section analysis is recommended to confirm the malignant nature of the tumor, to adapt the extent of resection and to indicate neck dissection. Whenever possible, the entire tumor and adjacent salivary or periglandular tissue should be sent for frozen section analysis.

CONCLUSION

Fine-needle cytology and frozen section analysis play an essential role in the management of salivary gland cancers.

Myoepithelial Carcinoma Ex-Pleomorphic Adenoma: A Rare Pathology Misdiagnosed as Pleomorphic Adenoma; With a Novel TERT Promoter Mutation and High PD-L1 Expression

Myoepithelial carcinoma (MECA) is a rare salivary gland (SG) neoplasm (0.1-0.45% of all SG tumors) that often presents with bland cytomorphology and can be misclassified as cellular pleomorphic adenoma (PA) or myoepithelioma. This is particularly challenging in MECA ex-PA cases, especially if tumor shows minimal to no capsular invasion. We report a rare case of a 76-year-old female; history of left superficial parotidectomy with diagnosis (outside hospital) of cellular PA, who re-presented 9 months post surgery with enlarging left parotid mass, neck lymphadenopathy and facial nerve deficits. FNAB of parotid and neck lymph node revealed cellular aspirates with loosely cohesive clusters of myoepithelial cells with occasional chondromyxoid stroma. Prior resection slides were reviewed, and diagnosis of MECA ex-PA was made. Patient underwent left radical parotidectomy, selective neck dissection, with facial nerve sacrifice (due to extensive encasing by tumor). Histology showed a multinodular tumor with pushing borders, zonal arrangement comprising of a hypocellular, necrotic/myxoid center, and a peripheral rim of myoepithelial cells, confirmed by positive S100, and p63. Tumor extensively infiltrated peri parotid soft tissues with multiple foci of lymphovascular and perineural invasion; and metastatic neck lymph nodes. Next generation sequencing revealed a novel TERT promoter mutation (c.-124C > T), not usually described in SG neoplasms. Further, PD-L1 immunohistochemistry showed positive expression, making patient eligible for anti-PDL-1 immunotherapy. This case highlights importance of recognizing the subtle malignant features of MECA in distinguishing it from benign mimics like PA. In addition, presence of TERT mutation opens a new arena for future research to explore potential treatment targets.

Myoepithelial Carcinoma Arising in a Plasmacytoid Myoepithelioma of the Parotid Gland Synchronized with Melanoma: A Case Report and Review of the Literature

Myoepithelial carcinoma, also known as malignant myoepithelioma, is considered an extremely rare (0.45-1%) malignant salivary gland neoplasm. Approximately 100 cases have been reported in the English-language literature on myoepithelial carcinoma. The majority of the myoepitheliomas described in the literature have been benign, and the malignant counterpart is considered rare (<1%). Such a tumor may appear de novo or rarely develop from a preexisting pleomorphic adenoma (<20%), and in exceedingly rare cases (<0.5%), it has arisen from a benign myoepithelioma (i.e., plasmacytoid myoepithelioma). To our knowledge, no case of myoepithelial carcinoma of the parotid gland arising in a plasmacytoid myoepithelioma synchronized with melanoma has been reported to date. The treatment of myoepithelial carcinoma has been mainly surgical, including wide excision with free margins, with or without nodal dissection. The roles of chemotherapy and radiotherapy have not yet been established. We report a case of myoepithelial carcinoma of the parotid gland arising in a plasmacytoid myoepithelioma synchronized with melanoma in a 40-year-old woman. In our case, a complete response was achieved with surgery followed by adjuvant chemotherapy based on carboplatin and paclitaxel concurrent with radiotherapy.

Myoepithelial carcinoma of the salivary gland: pathologic and CT imaging characteristics (report of 10 cases and literature review)

OBJECTIVE

To summarize the pathologic and computed tomography (CT) imaging characteristics of myoepithelial carcinoma in the salivary gland.

STUDY DESIGN

Ten patients with myoepithelial carcinoma of the salivary gland underwent enhanced CT scanning, and the pathologic and CT imaging features were evaluated, including the pathologic type, size, margin morphology, and enhancement pattern of the lesions.

RESULTS

Myoepithelial carcinoma had a multinodular or lobulated outline. The cut surfaces were gray-brown with no or incomplete capsules, and visible bleeding was observed in some cases. The pathologic cell type of the tumor was spindle-shaped, clear, plasmacytoid, or epithelioid cells or a mixture of cell types. Nonenhanced CT imaging showed an irregular lobulated or multinodular lesion with ill-defined margins and inhomogeneous attenuation and punctate calcification in a minority of the lesions. The enhanced CT imaging results revealed moderate and intense inhomogeneous enhancement, including cystic and slit-like regions with no enhancement, intense nodular enhancement, and small tortuous vessels in the arterial phase.

CONCLUSION

The pathologic features and CT imaging findings of myoepithelial carcinoma were characteristic, and familiarity with these imaging findings might aid in the diagnosis of this entity.

Malignant myoepithelioma of the maxilla posing a diagnostic dilemma

Malignant myoepithelioma is an extremely rare tumor of the salivary glands. Myoepitheliomas make up less than 1% of all salivary gland tumors. We report of a case of malignant myoepithelioma of the upper jaw in a 55-year old man. The tumor primarily arose from the maxillary sinus and secondarily involved the palate. A diagnosis of pleomorphic adenoma was interpreted, following fine needle aspiration cytology and spindle cell tumor, following incision biopsy with a dilemma. The surgery consisted of subtotal maxillectomy preserving the infra orbital rim and posterior wall of the maxillary sinus, with wide local resection. Neck dissection was not carried out. The final histologic diagnosis of the tumor proper was made out to be malignant myoepithelioma. Three different diagnoses were made in dilemma to reach out the final diagnosis, which was confirmed by immunohistochemistry. The case presented and discussed, underscores the importance of diagnosis and treatment of this rare clinicopathologic entity.

Expression of hMLH1 and hMSH2 proteins in pleomorphic adenoma of minor salivary glands: relationship with clinical and histologic findings

OBJECTIVE

The aim was to examine the relationship between clinicopathological features and immunoexpression of hMLH1 and hMSH2 proteins in pleomorphic adenoma (PA) of minor salivary glands.

STUDY DESIGN

Paraffin-embedded samples of typically benign PA lesions (n = 35) were prepared for histologic and immunohistochemical assessment. Based on the clinicopathologic features, the samples were categorized into low- and high-risk subtypes for their estimated potential for malignant transformation.

RESULTS

Immunohistochemical analysis revealed strong correlations regarding the expression estimation and staining-intensity distribution (SID) scores between the two proteins. Although there was no relationship between marker immunoexpression and SID scores regarding clinical parameters, statistically significant variations for these parameters were evident regarding some histologic criteria or for risk stratification subtypes.

CONCLUSION

The findings of this study could suggest the relationship of a DNA mismatch repair deficiency with high-risk subtypes of PA and the implication of its role in the origin and progression of these subtypes.

Immunohistochemical expression of p63 in pleomorphic adenomas and carcinomas ex-pleomorphic adenomas of salivary glands

Alteration of the p63 protein expression has been associated with several human cancers including salivary gland tumors. We sought to assess the p63 expression in pleomorphic adenomas (PA) and carcinoma ex-pleomorphic adenomas (Ca ex-PA), since this protein has been related to myoepithelial phenotype and the biological behavior of cancer. Ten samples of PA and ten of Ca ex-PA were submitted to immunohistochemistry using a monoclonal anti-p63 antibody, clone 4A4. p63 was regularly expressed in myoepithelial cells' nuclei of the normal glandular parenchyma and in PA, but it was completely absent in five out of the ten samples of Ca ex-PA. (P < 0.05 by Fisher's exact test). Apparently, only those cases depicting some myoepithelial differentiation were positive. Our data suggest that loss of myoepithelial differentiation is important in the evolution of Ca ex-PA, and corroborate the hypothesis that p63 antigen may be a useful marker of myoepithelial cells in salivary glands neoplasms.