Mucoepidermoid carcinoma: a five-decade journey

Area of Science:

• Pathology
• Oncology
• Histopathology

Background:

• Mucoepidermoid carcinoma (MEC) lacks a universally accepted grading system, hindering accurate diagnosis and prognosis.
• Recent debates focus on the prevalence of CRTC1-MAML2 rearrangement in high-grade (HG) MEC, suggesting potential diagnostic challenges.
• Morphologic classification difficulties may contribute to the inconsistent grading of MECs.

Purpose of the Study:

• To investigate historical diagnostic challenges in mucoepidermoid carcinoma (MEC) grading.
• To identify neoplasms that are frequently misdiagnosed as high-grade (HG) MEC.
• To analyze the association between diagnostic accuracy, clinicopathologic features, and CRTC1-MAML2 rearrangement in MEC.

Main Methods:

• Retrospective review of 46 alleged MEC cases diagnosed between 1956 and 1974.
• Re-evaluation of histopathologic diagnoses, comparing confirmed MECs with revised diagnoses.
• Analysis of clinicopathologic features (metastasis, invasion, survival) and CRTC1-MAML2 rearrangement in a subset of confirmed MEC cases.

Main Results:

• Of 46 reviewed cases, MEC diagnosis was confirmed in 22, while 24 were reclassified.
• Cases with revised diagnoses showed higher rates of lymph node metastasis, perineural invasion, and poorer survival compared to confirmed MEC.
• Adenosquamous carcinoma, squamous cell carcinoma, and salivary duct carcinoma were the most common mimics of HG MEC. CRTC1-MAML2 rearrangement was detected in 5 low-grade, 7 intermediate-grade, and 2 HG MEC cases.

Conclusions:

• Histologic grading of MEC is complicated by the frequent misdiagnosis of other salivary gland neoplasms, particularly high-grade variants.
• Accurate differentiation from mimics like adenosquamous carcinoma and salivary duct carcinoma is crucial for appropriate patient management.
• The variable presence of CRTC1-MAML2 rearrangement across MEC grades underscores the need for refined diagnostic criteria beyond molecular markers.