Mucoepidermoid Carcinoma
Key Points
Mucoepidermoid carcinoma (MEC) is a highly malignant epithelial neoplasm comprising mucus-secreting, proliferating squamous, and nondescript intermediate epidermoid cells
Although the pathophysiology is unclear, a novel translocation fusion oncogene, MECT1-MAML2, is present in 34% to 81% of MECs of the salivary glands, but it has not been identified in eyelid or lacrimal sac MECs
In the ocular adnexa, about 80% of cases involve the conjunctiva, followed by the lacrimal sac (17%), and the eyelid skin (3%)
It appears as a red, pink, yellow, brownish, or leukoplakic nodular or pedunculated conjunctival mass
When the lacrimal sac is involved, symptoms may include epiphora, associated with dacryocystitis, or a palpable medial canthal mass
The recommended treatment is surgical excision with wide margins; with orbital extension, enucleation or even orbital exenteration may be indicated
MEC tends to be aggressive locally and regionally and recurrence rates after surgical excision range from 70% to 100%
Mucoepidermoid carcinoma (MEC) is a highly malignant epithelial neoplasm comprising mucus-secreting, proliferating squamous, and nondescript intermediate epidermoid cells. The term “mucoepidermoid” tumor was originally introduced by Stewart et al in 1945,1 for tumors having two principal histologic elements, mucus-secreting cells and epidermoid cells. Mucoepidermoid tumors primarily occur in the major salivary glands.1,2,3 They have also been reported in the minor salivary glands,4,5 in the upper respiratory tract (larynx, trachea, or bronchi),4,5,6,7,8 and in the nasal mucosa,9 liver,10 anus,9 maxilla,11 mandible,12 uterine cervices,9 and penis.13 These tumors rarely arise from the skin.14,15,16 In the periocular region, MEC primarily involves the conjunctiva,17,18,19,20,21,22,23,24 lacrimal sac,25,26 and lacrimal gland.27,28 It very rarely arises in the eyelid skin.20,29,30,31,32,33,34
Etiology and Pathogenesis
There have been very few studies on the genetic changes associated with MEC. A novel translocation fusion oncogene, MECT1-MAML2, between chromosomes 11 and 19 was described in 2003.35,36,37 This gene product is present in 34% to 81% of MECs of the salivary glands.38 It is related to tumorigenesis, and knockdown of the protein product inhibits tumor growth.39 However, MAML2 rearrangement has not been identified in the eyelid or lacrimal sac MECs.
Several studies examined epidermal growth factor receptor (EGFR) signaling in the etiology of MEC and suggested that this pathway might play a role in its pathogenesis. Also, mutations in p53 have been identified in MEC of the salivary gland.37,40 There is a correlation between p53 expression and the proliferation marker Ki-67, suggesting that mutations in p53 might represent a genetic switch associated with the transformation of a low-grade tumor to a high-grade one.41
Clinical Presentation
In the ocular adnexa, about 80% of cases involve the conjunctiva, followed by the lacrimal sac (17%), and the eyelid (3%). Only 11 cases of eyelid MEC have been reported in the literature.29,30,31,32,34,42,43,44,45,46 Males are affected more commonly than females (76%-80%) for periocular MEC,47 but for eyelid lesions, there is no gender predilection.42 About 80% of eyelid lesions involve the lower eyelid.42 The duration of symptoms before presentation is relatively short, usually 2 to 6 months, but occasionally progression can be indolent over many years.30,42
In most cases, the lesion involves the bulbar conjunctiva near the corneal limbus (70%), with rare occurrences in the conjunctival fornix or eyelid skin (Figure 140.1).24 Aggressive lesions may invade the orbit, seen in about 20% of cases, and rarely the tumor can invade an adjacent paranasal sinus.29,47,48,49 The most common periocular presentation is a painless, rapidly progressive conjunctival or eyelid cutaneous mass.42 Lesions may appear as a red, pink, yellow, brownish, or leukoplakic nodular or pedunculated mass that may be irritated or occasionally ulcerated. When the lacrimal sac is involved, symptoms may include epiphora associated with dacryocystitis and a palpable medial canthal mass. Regional lymph node involvement has been described, but distant metastasis is very unusual.18,43
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