Mucoepidermoid carcinoma of the breast
Mucoepidermoid carcinoma is an uncommon type of breast cancer that resembles mucoepidermoid cancers of the salivary glands.
Indeed, there are generally three distinct elements, in varying degrees, that compose mucoepidermoid breast cancer.
- Mucus-secreting cells
- Squamous cells,
- Intermediate cells.
This type of cancer is most common in the salivary glands (accounting for about 35% of salivary gland cancers) but may occur at distant sites, such as the breast.
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The characteristics of mucoepidermoid carcinoma under the microscope are sheets of epidermoid cells with areas of definite squamous differentiation. There are also often glandular and cystic spaces with a lining of atypical mucin-secreting columnar cells.
Mucoepidermoid Carcinoma of the breast typically show both a low and high grade variety
Mucoepidermoid carcinoma of the breast seems to occur in two distinct grades; low and high.
So, the low-grade mucoepidermoid carcinoma tends to grow slowly, appears in any age group. Treatment is easy, with surgical excision.
However, the high-grade type of mucoepidermoid carcinoma of the breast is very aggressive and frequently produces lymph node and distant metastases.
High grade tumors will tend to show areas of focal necrosis, with epidermoid and mucinous cells found only in isolated spots. Unfortunately, the prognosis for a high-grade mucoepidermoid carcinoma of the breast is rather poor.
Clinical presentation of Mucoepidermoid Carcinoma of the Breast
Clinically, a mucoepidermoid breast cancer tumor will often present as a mass with an unclear margin, often in the upper outer area of the breast.
Both mammography and ultrasonography will typically show a mass with an irregular shape that is suggestive of breast cancer. Quite often, these tumors will be either wholly or partially cystic.
Histological features of mucoepidermoid carcinoma of the breast
Cytologically, mucoepidermoid carcinoma will usually show as solid clusters of two types of cancer cells:-
- Cells with mucus in the cytoplasm
- Cells without mucus.
There will be mixtures of neoplastic mucus-secreting, squamous, and certain ‘intermediate’ cells, that have characteristics of both.
More specifically, an ultra structural examination of the tumor will tend to show squamous cells, mucus-secreting luminal cells and classic myoepithelial cells.
Intermediate cells will often contain focal peripheral myofilaments and dense bodies and pinocytotic vesicles associated with centrally aggregated tonofilaments. Specialists tend to be interpret these cells as modified myoepithelial cells.
Mucoepidermoid breast cancer tumors will often be surrounded by a fibrous pseudocapsule. Possibly, intraductal carcinoma foci and invasive cancer nests make up this capsule.
Where there is stromal invasion, one will probably find many solid nests composed of mucus-containing and squamous cancer cells. But, there is quite often no ‘generic’ invasive ductal carcinoma component in these tumors.
Low grade mucoepidermoid breast cancers are often Er and PR negative
In the low-grade variety of mucoepidermoid breast carcinoma, the squamous cells will quite often show keratinization and glandular cells forming distinct small lumina.
High grade mucoepidermoid carcinomas will usually show clusters of epithelial ductal cells with a mix of glandular, squamous and intermediate cells. There may also be scant intra and extra cellular mucin.
High grade tumors will often feature a large undifferentiated component to the tumor, necrosis and prominence of mitoses. If this is the case, then medics predict an aggressive course for the carcinoma. .
On the other hand, if the tumor shows a high degree of histological differentiation, this would tend to suggest a more indolent behavior overall. Additional, mucoepidermoid breast tumors are frequently estrogen and progesterone receptor negative.
Immunohistochemical characteristics of Mucoepidermoid Carcinoma of the Breast
Mucoepidermoid carcinoma of the breast will usually show clusters of epithelial ductal cells displaying a mixture of glandular, squamous and intermediate cells.
These type of cells will usually stain with S-100 protein, EMA, CEA and epidermal cytokeratin. The intra and extracurricular mucous substance will also stain quite easily. However, the higher-grade tumors tend to have less of these elements.
Higher grade tumors may stain more readily for periodic acid-Schiff, keratin, epithelial membrane antigen and carcinoembryonic antigen. Also, if there is also a high expression of Ki-67, this tends to support a prediction of high tumor aggressiveness.
Treatment and Prognosis for Breast Mucoepidermoid Carcinoma
Medics consider low grade mucoepidermoid carcinomas of the breast, with good squamous and adenomatous cell differentiation, to have a very favorable prognosis.
Surgeons will often treat these types of by either surgical excision or mastectomy, and in most cases there is no local recurrence and no nodal metastasis.
Most patients who have undergone treatment for low-grade mucoepidermoid carcinoma of the brease remain disease free 10 years later, and with no lymph node involvement.
High grade mucoepidermoid breast cancers have a less positive prognosis
High-grade variants of mucoepidermoid breast carcinoma, however, have a much poorer outlook. Lymph node and distant metastases is common. It would be a bit less likely for a patient with high grade mucoepidermoid breast carcinoma to survive beyond 5 years. But with proper interventions and a little good luck, this has been know to occur.
The clinical course for a high grade mucoepidermoid breast cancer, however, is often rather poor and quite rapid. Widespread and systemic disease is quite common, even with chemical, radiation, and hormonal therapies.
- Horii R, Akiyama F, Ikenaga M, Iwase T, Sakamoto G. (2006) Muco-epidermoid carcinoma of the breast. Pathol Int. 2006 Sep;56(9):549-53. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5758243/
- Hornychová H, Ryska A, Betlach J, Bohác R, Cízek T, Tomsová M, Obermannová R. (2007) Mucoepidermoid carcinoma of the breast. Neoplasma. 2007;54(2):168-72. https://www.ncbi.nlm.nih.gov/pubmed/17319792
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