Oncocytic Carcinoma of the Breast
Oncocytic carcinoma of the breast has also been referred to historically as malignant oncocytoma and mammary epithelial oncocytoma. It is an extremely rare form of breast cancer, and usually develops at an older age. Oncocytic breast carcinoma may develop in men as well. If a particular breast cancer tumor is characterized by more than 60% to 70% oncocytic cells, then the tumor will usually be referred to as oncocytic breast carcinoma.
Because this topic is extremely unpopular on the internet, I would recommend still using this page, even though I have created a new version with more up-to-date information on Rare Types of Breast Cancers.
‘Oncocytic‘ means ‘swollen cells‘, and in the case of oncocytic breast carcinoma the ‘swelling‘ is due to the accumulation of mitochondria.
In other words, an oncocyte is a cell swollen with eosinophilic, granular cytoplasm which, at ultrastructural level, appears to be filled with numerous mitochondria. Most oncocytic tumors in other areas of the body are benign, but breast oncocytic tumors are not necessarily so benign. However, there have been too few cases to make generalization about prognosis for oncocytic breast carcinomas.
Histological features of Oncocytic Carcinoma of the Breast
Generally speaking, the histological characteristics of oncocytic carcinoma of the breast is about the same as oncocytic tumors that occur at other locations, such as salivary glands and endocrine organs. With oncocytic breast carcinomas, the neoplastic cells tend to be arranged in large aggregates which show focal ductal differentiation. Oncocytic breast carcinomas tend to be mostly solid without glandular differentiation, and not diffusely cribriform either.
Oncocytic breast tumors require certain stains
It can be difficult to distinguish oncocytic breast carcinoma from apocrine breast carcinoma through the use of H and E stains. However, oncocytic carcinoma of the breast will typically be negative for GCDFP15 and positive for the anti mitochondrial antibody. The anti mitochondria antibodies demonstrate that the neoplastic cells are filled with numerous mitochondria.
(Mitochondria are membrane-bound organelles, and like the nucleus have a double membrane. They are responsible for giving a cell its ‘moving power‘)
Breast oncocytic carcinomas tend to be ER and PR positive
Oncocytic carcinoma of the breast will also typically be negative for chromogranin and synaptophysin, and negative for smooth muscle actin. If the oncocytic carcinoma is in an ‘in situ‘ stage, then the peripheral myoepithelial cells may best positive for smooth muscle actin. ER and PR are usually positive in oncocytic breast tumors, but this will naturally vary for specific breast tumors.
Tumors typically show significant amounts of mitochondria
Cytologically, oncocytic breast carcinoma is characterized by sharp cell borders, and with large, round or vesicular nuclei with prominent nucleoli. Typically, cells have abundant granular cytoplasm. Indistinguishable from apocrine carcinoma on H&E stain. with oncocytic breast cancers, mitochondria quite often occupy at least 60% of the cytoplasm, diffusely distributed, which will be evident from the staining process.
The prognosis for oncocytic carcinoma of the breast is highly positive
Oncocytic breast carcinomas tend to have a very favourable outlook. They need to be treated, but are usually treated successfully. Mastectomy is usually undertaken, and chemical and radiation therapy are often not required. They are so uncommon, however, that generalizations are difficult.
For further reading, I suggest you go to this page that has a bunch of information on pleomorphic adenoma of the breast, as well as this page which has material about cytoplasm.
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