Epithelial-Myoepithelial Carcinoma of the Parotid Gland Misdiagnosed as Rhabdomyosarcoma and Non-Hodgkin Lymphoma: A Case Report of a Diagnostic Dilemma

ABSTRACT Background: Epithelial-myoepithelial carcinoma (EMC) is a rare biphasic salivary gland malignancy that can pose diagnostic challenges. We describe a 52-year-old man whose recurrent right parotid and upper-neck mass was initially considered rhabdomyosarcoma and subsequently non-Hodgkin lymphoma (NHL), before reassessment favoured EMC. Case Report: After an initial biopsy suggesting rhabdomyosarcoma, the patient underwent excision at a private facility. Postoperative histopathology suggested NHL, and lymphoma-directed chemotherapy was unsuccessful. Initial immunohistochemistry (IHC) showed CD45, CD10 and pancytokeratin reactivity, producing an inconclusive interpretation. He was referred for reassessment with a recurrent right parotid, submandibular and upper-neck mass and cervical and axillary lymphadenopathy. Ultrasound demonstrated a heterogeneous mass, while magnetic resonance imaging demonstrated an extensive multinodular, multilobulated neck lesion. Cytology identified malignancy, possibly salivary adenocarcinoma. Repeat biopsy showed clear-cell myoepithelial-appearing tumour cells in nests and sheets with prominent basement-membrane material and hyalinization. IHC demonstrated pancytokeratin and vimentin positivity. The integrated morphologic and immunophenotypic findings supported a diagnosis of EMC, although the limited panel restricts definitive exclusion of mimics. The lesion was considered unresectable; six cycles of chemotherapy were administered at three-week intervals. Clinical reduction of the mass was reported, with no recurrence reported more than one year after treatment. Conclusion: Reassessment of a recurrent salivary-region tumour after discordant diagnoses can clarify management. Morphology should be interpreted alongside a sufficiently discriminating IHC panel; limited marker positivity alone does notestablish EMC. This case illustrates the importance of diagnostic review when treatment response is unexpected. Keywords: epithelial-myoepithelial carcinoma, rhabdomyosarcoma, non-Hodgkin lymphoma, case report, histopathology, immunohistochemistry