Pleomorphic adenoma of the breast
A ‘pleomorphic‘ adenoma is a very rare sub-type of breast adenoma, which is a proliferative neoplasm in some combination of glandular, fibrous, and fat tissues. These generally benign tumors are usually asymptomatic and unless they have grown into a palpable lump, they would generally only be detected through imaging studies done for some other reason. It will typically develop in the subareolar region of the breast (below the nipple). However, pleomorphic adenomas are not as clearly benign as other breast adenomas, and in some instances will develop into low grade breast carcinomas.
Men can also develop pleomorphic breast adenomas
Pleomorphic breast adenomas are so-named because they share similar morphological characteristics to the ‘true‘ pleomorphic adenomas, which are the most common benign tumors of the salivary glands, the parotid gland in particular. Both breast glands and salivary glands are ‘tubulo-acinar‘ exocrine glands (meaning they are designed for secretion), so it is not surprising that adenomas developing from those glands would have similar histological and morphological features. Men can also develop pleomorphic breast adenomas, though women develop the lesion at 10 times the rate for men.
Diagnostic histology of pleomorphic breast adenoma
Pleomorphic adenomas show a diverse histology, and may contain epithelial, myoepithelial and mesenchymal-type cells. The architectural patterns and cell formations in these lesions are highly varied, or ‘pleomorphic‘ so to speak. Breast pleomorphic adenomas tend to have well circumscribed margins, and often a central area of cartilaginous tissue. The cytologic presentation of pleomporhic adenoma can mimic other carcinomas however, such as colloid carcinoma or possibly phyllodes tumor. As with all breast adenomas, a combination of cross referenced biopsy, X-ray, and ultrasound studies is typically required for an accurate diagnosis.
Two types of breast pleomorphic adenoma: myoepithelial differentiation
Pleomorphic , or ‘salivary gland-like‘ tumors actual present in two variations with an important distinction: whether or not there is evidence of ‘myoepithelial differentiation‘. The term ‘differentiation‘ can be taken in the context of genetics, and a well-differentiated cell is one which forms and functions into the type of cell or gland that it was supposed to. However it is sometimes also used to describe a ‘unique‘ or ‘differentiated‘ aspect of a tumor, within a general category, and that is the case here. A pleomorphic adenoma with myoepithelial differentiation is one in which there is a layer of myoepithelial cells present.
Myoepithelial pleomorphic breast adenomas are benign
Pleomorphic adenomas with myoepithelial differentiation are benign, and the conditions is sometimes referred to as ‘benign myoepithelioma‘. But other pleomorphic adenomas, with myoepithelial differentiation can develop into low grade carcinomas such as adenomyoepithelioma, adenoid cystic carcinoma, and adenosquamous carcinoma. As with all breast adenomas, there remains the small possibility that carcinoma could be developing secondarily in the background of a pre-existent benign pleomorphic adenoma. If this occurs, it is termed ‘carcinoma ex pleomorphic adenoma‘. It is not yet understood why this happens, or which pleomorphic adenoma cells are prone to malignant transformation. Rare cases of higher grade malignant myoepithelioma have also been reported.
Some pleomorphic breast adenomas are at higher risk for breast cancer development
Pleomorphic adenomas which are not ‘differentiated‘ by a layer of myoepithelial cells are thought to be of a higher risk for malignancy, though some of these sub-categories of breast cancer have only recently been recognized. Undifferentiated myoepithelial pleomorphic carcinomas include acinic cell breast carcinoma, oncocytic breast carcinoma, and mucoepidermoid breast carcinoma, which is very rare.
Treatment and breast cancer risk for pleomorphic breast adenoma
Pleomorphic adenoma in the breast is a very rare and benign lesion with extremely rare cases of malignant transformation. However, there is some history of malignant degeneration of pleomorphic adenomas occuring in other areas of the body, and for this reason even benign pleomorphic lesions are thought to contain a slightly higher risk for breast cancer development. Typically, the tumor will be surgically excised. The main issue for the patient with a pleomorphic adenoma is that, since it contains histologic features that resemble those of malignant breast cancers, it can be misdiagnosed (over-estimated), possibly resulting in an unwarranted mastectomy.
Below are some Q&A…
- How is pleomorphic adenoma diagnosed? Fine needle aspiration, and core needle biopsy.
- What is the treatment for pleomorphic adenoma? Wide local excision is the most effective way to get rid of the tumor. (25% recur), recurrence are usually within 18 months, but an be up to 50 year later. After surgery for recurrent tumor, 25% recur again.
- What are the risk factors? Submandibular location, older age, larger in size, prominent hyalinization, increased mitotic rate, and radiation exposure.
- At what age does it mostly occur? Often occurs in women in their 30’s, but can occur in any age.
- What does pleomorphic adenoma look like? Circumscribed, single or multiple yellow-whire firm nodules sized at 1-4 cm, and often subareolar.
- What are some other micro descriptions about pleomorphic adenoma? It is similar to counterpart in salivary glands or skin, fibrous pseudocapsule surrounds benign glandular epithelial and myoepithelial cell sin chondromyxoid or osseous stroma, epithelial cells are arranged in tubules, islands, cords, or sheets, are cuboidal or columnar with brand nuclear features and minimal mitotic figures, myoepithelial cells are polygonal or stellate with clear to eosinophilic cytoplasm and small nuclei.
- How fast does pleomorphic adenoma grow? It is very slow growing.
- What causes pleomorphic adenoma? It is caused by blockages, but its occurrence has been linked with smoking and exposure to radiation.
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