Schwannoma is a rare and benign neoplasm which develops out of ‘Schwann‘ cells, or nerve sheath cells. Sometimes also referred to as a neurilemmoma, neurinoma, or peripheral nerve sheath tumor, schwannomas usually develop in the extremities and the trunk and head regions, but they have been known to develop in the breast.
This page is getting a little bit old and a little bit out-dated, but don’t get me wrong, just because it is, doesn’t mean that you have to quit using it – this page really does have a lot of great research material. However, I have created a newer version with more up-to-date information on Schwannoma of the Breast.
The concern with breast schwannoma is that a correct differential diagnosis is obtained, because they can resemble a malignant neoplasm (breast cancer) mammographically.
Most breast cancers and other breast tumors have an epithelial cell origin, with stromal and myoepithelial cell tumors being less common. A nerve sheath tumor arising from neural crest-derived Schwann cells within the breast is rarer still. Schwann cells produce myelin, which is a substance that insulates nerves and facilitates neural transmission.
For unknown reasons, these cells can sometimes grow in a neoplastic fashion which results in a benign tumor. But they are not always benign, however. There is the remote possibility of a Schwannoma developing malignant cellular characteristics, which is termed a malignant peripheral nerve sheath tumor of the breast.
Susceptibility to breast schwannoma
Breast Schwannoma affects slightly more females than males, and tends to affect adults in the 20 to 50 years range, or a younger subgroup than one would typically find for breast cancer. There is some evidence to suggest that breast schwannomas may also develop at a previous site of radiation therapy, and this can even occur after a delay of up to 20 years. It may be estimated that about 10% of breast schwannomas originate due to prior radiation treatments.
Breast Schwannoma and Neuro-fibromatosis
Schwannomas are rare in the breast, and are often associated with a genetic condition called neurofibromatosis (NF), which can effect many areas of the body. There are two basic types of neurofibromatosis. “Type 2” can be associated with schwannomas, while “Type 1” NF is associated with neurofibromas.
Neurofibromatosis-2 (NF-2), also called ‘central von Recklinghausen’s disease‘ is an autosomal dominant hereditary disease, which affects approximately 1 in 50,000 individuals. NF-2 can cause multiple neoplasms to the head, spine, and other areas including the breast, and schwannoma is one of the most common manifestations of these neoplasms (glioma and meningioma are also common).
NF2 breast schwannomas have a higher potential for malignancy
A distinction can often be made between these NF-2 schwannomas, which often occur in multiples in various body areas, and ‘sporadic‘ breast schwannomas which may have other causes. These genetic-hereditary NF-2 schwannomas also tend to occur at a younger age. Approximately 60% of breast schwannomas will show evidence of NF-2 mutations, while about 40% show no detectable gene mutation at all.
It is an important distinction, however, as NF2 schwannomas tend to have a significantly higher malignant-proliferation potential than sporadic tumors, and can be indicative a more widespread disease.
Diagnosis of breast schwannoma
A schwannoma which presents as a palpable breast lump will typically be smooth, elastic-soft, mobile, and painless. When discovered mammographically, perhaps during a routine breast cancer screening, schwannoma will typically appear as a well-circumscribed, oval-shaped nodule without microcalcifications. Increased density will be apparent, but the margins are not always so well defined in all cases.
Ultrasound imaging of a breast schwannoma will tend to reveal a well-demarcated, hypoechoic solid mass, usually with posterior enhancement. It is also possible for schwannoma to have a cystic element (fluid components). It is difficult through mammography and ultrasound alone to arrive at a definitive diagnosis of breast schwannoma.
This kind of breast tumor is usually benign, but very large tumor, (greater than 5 cm in diameter) demonstrating heterogeneity and will ill-defined margins, might be more suspicious of a malignant situation.
Histological properties of breast schwannoma
Analysis of a breast schwannoma will typically show several clusters of elongated ‘spindle cells‘, indicative of a neoplasm of mesenchymal origin, in a palisading pattern. These spindle-shaped cells may have irregular contours with curved cores, and the background cytoplasm might be slightly colored.
Breast schwannoma will almost always stain positive for S-100 proteins, which are characteristic of schwannoma. If a tumor is larger than 5 cm, one may find hemorrhagic and necrotic areas inside the mass. Benign schwannomas may also contain rosette-like structures which can mimic the appearance of neuroblastoma or primitive neuroectodermal tumors (PNET).
If an electron microscope is used, the most prominent feature of Schwann cells is a well-developed basal lamina.
‘Antoni A‘ and ‘Antoni B‘ densities of breast schwannoma
The cellular density and organization within breast schwannoma is variable, but they will all typically show ‘Antoni A‘ and ‘Antoni B‘ areas.
‘Antoni A areas‘ are typically composed of compact spindle cells, often with ‘twisted‘ nuclei and with indistinct cytoplasmic borders. They are usually arranged in interlacing fascicles. Antoni A areas usually show the highest concentrations of S100 protein.
‘Antoni B areas‘, on the other hand, are far less orderly and less cellular. They usually consist of a loose meshwork of gelatinous and microcystic tissues, with large, irregularly spaced and thick-walled blood vessels. The spindle or oval cells are usually arranged in a haphazard fashion within loosely textured matrices.
Sometimes the cells are arranged in a palisade fashion with their nuclei aligned, occasionally forming rounded Verocay bodies. But, most of the time a breast schwannoma will show a kind of wave-like alternation of these two kinds of cellular densities.
NF2 schwannomas often show a ‘grape-like‘ pattern
If the breast schwannomas is thought to have arisen due to NF2 , cytologically it may show a lobular, or ‘grape-like‘ growth pattern. NF-2 tumors also tend to have more areas of high cellularity and these verocay bodies, as opposed to ‘sporadic‘ schwannomas.
Other subtypes of Schwannoma of the breast
There are several possible subcategories of breast schwannoma, depending largely upon cellular features, necrosis and mitoses, and other elements such as cysts. However, remember that schwannoma is a peripheral tumor most common in the trunk or head regions, and even though some of these subtypes are well documented, their presentation in the breast is very unlikely. These subtypes include plexiform, cellular, and ancient schwannomas.
Plexiform breast schwannoma
A ‘plexiform‘ Schwannoma might have a conventional, cellular, or mixed appearance. They tend to be superficial (dermal) tumors, which are only worrisome if they show mitoses and increased cellularity.
Cellular breast schwannoma
A ‘cellular‘ schwannoma is usually found in the deeper tissues, and feature compact simple shaped cells arranged in a fascicular or ‘whorled‘ growth pattern, and frequent mitosis. The tumor will typically be surrounded by a thick fibrous capsule containing a dense lymphocytic infiltrate. Cellular schwannoma is basically a ‘hyper-cellular‘ variant of schwannoma composed mainly of Antoni A tissue and devoid of Verocay bodies.
Ancient breast schwannoma
An ‘ancient‘ schwannoma will tend to display prominent degenerative changes. These might include cyst formation, calcification, hemorrhage, and hyalinization (conversion of arterioles into hyalin, a protein with a pink-glassy appearance after staining).
Ancient schwannomas also show prominent cellular atypia, with hyperchromatic nuclei and coarse clumping of chromatin, but mitotis is not characteristic. Ancient schwannomas are more common in the nasal cavity.
Treatment and prognosis for breast schwannoma
Schwannomas are rare and mostly benign, but due to the existent possibility of malignancy, they are usually removed surgically by radical or modified mastectomy. Radiation therapy is often used, with good effect, to decrease the likelihood of local recurrence. (But radiation therapy would not be used to treat breast schwannoma, if it was believed that earlier radiation treatments helped bring about the schwannoma in the first place).
Overall, it should be remembered that breast schwannoma is a completely different kind of disease than typical breast cancer (which tends to arise out of epithelial cells in the duct lining), and is generally benign. If a breast schwannoma is determined to have originated with neurofibromatosis type 2 as a genetically inherited disease, there can be many complications as the disease spreads.
On average, survival after the onset of a malignant peripheral nerve sheath tumor due to neurofibromatosis type 2 is about 15 years. In a situation where the Schwannoma shows malignant characteristics and has basically evolved into a ‘malignant peripheral nerve sheath tumor‘,(MPNST) the prognosis is generally poor. MPNST are highly aggressive tumors, with an overall 5 year survival rate of about 34%, and a 10 year survival rate of about 23%.
For further reading, I suggest you visit this page which has information on a histological workup for breast cancer diagnosis and treatment.
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