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.