Introduction
Malignant salivary gland tumours characterized by mucoepidermal differentiation with sclerotic stroma rich in lymphocytes and eosinophils have been designated the name sclerosing mucoepidermoid carcinoma with eosinophilia1-4 (SMECE). However, it has not been listed as an entity in the chapter on salivary gland, 2022 WHO Classification of Head and Neck Tumours5. Some reports highlighted the lack of MAML2 translocation in these tumours, as distinct from classical mucoepidermoid carcinoma (MEC) of the salivary glands. Some argued against grouping them under MEC based on their variable morphological features and the lack of MAML2 translocation. This counterargument is supported by the prominence of keratinization in the squamoid component and relatively reduced glandular or intermediate cell component noted in SMECE, such that other entities e.g. adenosquamous carcinoma should be considered in the differential diagnosis. The lack of a well-documented molecular marker also makes categorizing SMECE as a distinct entity difficult. A same-named tumour has been described in the thyroid6. The thyroid SMECE lacks common thyroid cancer mutations nor MAML2 translocation according to studies by Shah et al7. Whether SMECE of the head and neck region share similar histogenetic origin or molecular derangement requires further studies on larger tumour series. The underlying mechanism for the sclerotic stroma and eosinophilia has received little attention as these features could be seen in other tumours. We report a similar case in the parotid gland that was initially diagnosed as Langerhans cell histiocytosis due to the prominent Langerhans cell and eosinophilic reaction. It recurred 2 years later as a frank carcinoma fitting into the SMECE category by morphology. Molecular studies provided possible new understanding concerning the Langerhans cell and eosinophilic reaction.