Metastatic Thymic Mucoepidermoid Carcinoma: The Diagnostic Challenges and Role of CRTC1/MAML2 Translocation in Accurate Diagnosis and Treatment.

Mucoepidermoid carcinoma (MEC) is a subtype of epithelial neoplasms commonly found in salivary glands, but can also be seen in the thymus. Diagnosing MEC of the thymus is sometimes challenging due to its histological similarities with adenosquamous carcinoma (ASC). This case report describes a 64-year-old female with a history of metastatic endometrial adenocarcinoma who presented to an oncology clinic with a thymic mass as well as multiple mass lesions in the liver, bone, and abdominal wall. Initially diagnosed as thymic ASC based on histopathology, further genomic profiling revealed a CRTC1/MAML2 translocation, leading to the diagnosis of metastatic MEC of the thymus. Comprehensive genomic testing played a crucial role in distinguishing MEC from ASC. This case highlights the importance of genetic testing in cases of uncertain primary origins and in differentiating between morphologically similar tumors.