| disease | Mucoepidermoid Carcinoma |
| alias | Mucoepidermoid Tumor, Mucoepidermoid Carcinoma, Mucoepidemoid Tumor |
Mucoepidermoid carcinoma, also known as mucoepidermoid tumor, accounts for 5-10% of salivary gland tumors. Stewart et al. referred to it as mucoepidermoid tumor based on its clinical characteristics and histological features, further dividing it into benign and malignant categories. WHO also once adopted the term mucoepidermoid tumor. However, many scholars later argued that this nomenclature and classification were inappropriate, believing that all such tumors are malignant and should be termed mucoepidermoid carcinoma. Based on the degree of differentiation of the cancer cells and their biological behavior, they are classified into low-grade and high-grade malignant mucoepidermoid carcinomas. The 1990 WHO revision of the nomenclature and classification of salivary gland tumors adopted this classification method. Although the term "mucoepidermoid" is not entirely appropriate, it essentially reflects the tumor's main components: mucoid cells and epidermoid cells. Mucoepidermoid carcinoma originates from the epithelial cells of the glandular ducts.
bubble_chart Pathological Changes
(1) Gross Morphology Well-differentiated mucoepidermoid carcinoma resembles mixed tumors, appearing round and small in size, with a diameter mostly ranging from 2 to 3 cm, and rarely exceeding 5 cm. Some cases may have a capsule, but it is often incomplete or entirely absent. The cut surface is grayish-white or light pink, occasionally lobulated, and may contain varying numbers of small cysts filled with mucus. Poorly differentiated cases completely lack a capsule, with indistinct boundaries and invasion into adjacent tissues. The cut surface is grayish-white, non-lobulated, and uniformly textured, with scattered small cysts and translucent foci.
(2) Microscopic Examination Mucoepidermoid carcinoma is composed of mucinous cells, epidermoid cells, and intermediate cells. When mucinous cells are well-differentiated, they appear goblet-shaped or columnar, with clear cytoplasm and basally located nuclei; when poorly differentiated, they resemble adenocarcinoma cells, with mucus-containing cytoplasm that stains positive with carmine. Epidermoid cells resemble the stratified squamous epithelium of the oral mucosa, showing intercellular bridges and occasional keratinization. Intermediate cells are cuboidal, small, uniform in size, with scant cytoplasm, resembling basal epithelial cells. Intermediate cells can differentiate into mucinous or epidermoid cells. In well-differentiated cases, mucinous and epidermoid cells predominate, while intermediate cells are fewer. Tumor cells may form irregular sheets but often create cysts of varying sizes, lined with mucinous cells. Mucinous cells may overlay epidermoid cells or be interspersed among them. Larger cysts may have papillary projections, with mucus staining red in the lumen. In poorly differentiated cases, epidermoid and intermediate cells dominate, while mucinous cells are scarce. Tumor cells show significant atypia, mitotic figures are visible, solid epithelial masses are abundant, cysts are rare, and tumor invasion into surrounding tissues is evident.(3) Biological Characteristics Mucoepidermoid carcinoma often exhibits invasive growth, with a high recurrence rate and potential for lymph node metastasis. Metastasis to bone, brain, or lungs is rare. However, well-differentiated cases may have a complete capsule, and complete excision results in lower recurrence rates.
Mucoepidermoid carcinoma most commonly occurs in the parotid gland, accounting for more than 70% of cases. In minor salivary glands, it is frequently found in the palate, while other sites such as the retromolar area, buccal region, upper lip, and lower lip are less common. It can occur at any age but is most prevalent between 30 and 50 years old, with a higher incidence in females than males, approximately 1.5:1.
The clinical manifestations of mucoepidermoid carcinoma are closely related to its degree of differentiation. The well-differentiated type, which is the majority, typically presents as a painless mass that grows slowly and has a long course. The tumor size varies, with clear boundaries, firm consistency, mobility, and a smooth or nodular surface. It may be cystic or solid. When occurring in the palate or retromolar area, the mass may appear pale blue or dark purple beneath the mucous membrane, which is smooth and soft in texture. Puncture may yield a small amount of bloody, purplish-black fluid.
Poorly differentiated tumors grow more rapidly and are often accompanied by pain. The boundaries are unclear, with a diffuse nature and adhesion to surrounding tissues. They may ulcerate and become secondarily infected, forming persistent ulcerative surfaces with yellowish, viscous secretions. Sometimes, a salivary fistula may develop. When occurring in the parotid gland and involving the facial nerve, symptoms of facial nerve paralysis and facial muscle spasm may occur. In the palate, it may cause destruction of the hard palate.
The diagnosis is usually confirmed through intraoperative frozen section examination. For cases occurring in the parotid gland, sialography may reveal erosive destruction, ductal defects or interruptions, partial or complete absence of filling in the distal ducts, irregular duct walls, or even destruction of branch ducts, as well as malignant tumor manifestations such as contrast extravasation (iodine oil fistula). CT scans may show poorly defined masses with destruction or displacement of the parotid gland.
The primary treatment for mucoepidermoid carcinoma is radical local excision. To prevent recurrence, the tumor should be resected within normal tissue at least 1 cm beyond the tumor margin. For patients with high-grade mucoepidermoid carcinoma of the parotid gland undergoing initial surgery, regardless of the disease stage, total parotidectomy with preservation of the facial nerve is generally performed. Low-grade tumors have a higher likelihood of infiltrating the facial nerve; if the nerve is involved, total parotidectomy with sacrifice of the facial nerve should be performed. If the affected segment of the nerve is extensive, nerve grafting can be performed after resection. For mucoepidermoid carcinoma arising in the submandibular gland, submandibular triangle dissection is indicated. For tumors in the palate, partial maxillectomy is required. If the tumor has invaded surrounding tissues, extended resection should be performed.
The regional lymph node metastasis rate of mucoepidermoid carcinoma is relatively low. Except for low-grade tumors, where selective neck dissection may be considered, high-grade tumors generally do not require elective neck dissection. Perzik et al. emphasized that neck dissection should only be performed when lymph node metastasis is confirmed during the resection of the primary tumor.
Mucoepidermoid carcinoma is not sensitive to radiotherapy, but postoperative radiotherapy may be used for low-grade tumors to potentially improve efficacy or reduce recurrence.
Mucoepidermoid carcinoma has a favorable prognosis. Bhaskar reported 144 cases with a recurrence rate of 12.5% and a 5-year survival rate of 88.5%. The degree of tumor cell differentiation is closely related to the prognosis. Kosenfeld reported that the 5-year and 10-year survival rates for the well-differentiated type were both 100%, while for the poorly differentiated type, they were 39% and 11%, respectively. Spiro et al. reported 367 cases, with 5-year, 10-year, and 15-year survival rates for the well-differentiated type being 92%, 90%, and 82%, respectively, while for the poorly differentiated type, they were 49%, 42%, and 33%, respectively. Tumors originating in the parotid gland and minor salivary glands have a better prognosis than those in the submandibular gland. Lin Guochu et al. reported 189 cases with a local recurrence rate of 13.57%, and 5-year, 10-year, and 15-year survival rates of 91.66%, 89.87%, and 66.61%, respectively.
