A granular cell tumor, sometimes also called breast granular cell myoblastoma, is an uncommon neoplastic cell growth than originates in the Schwann cells of the peripheral nervous system. Most of the time, these tumors grow in the head and neck region, but they occur in the breast in about 6% of cases. Breast granular cell tumors are usually benign, but there are some rare examples of malignant presentation. Granular cell breast tumors can take a while to diagnose, and it is usually quite a relief when they are confirmed because they can mimic breast cancer. Mammographic findings are typically suspicious-looking, and these breast tumors can also simulate carcinoma due to their fibrous consistency, fixation to the pectoral fascia, and common skin retraction and ulceration. The average age of diagnosis for breast granular cell tumors is about 40, but they can actually happen at any age.
Granular cell breast tumors are generally 3cm or smaller. They usually have well-circumscribed margins, but can on occasion show infiltrative margins, which is more suggestive of a malignant breast cancer lesion. They were originally discovered in 1926 by Abrikossoff, who gave it the original name of 'granular cell myoblastoma.' Breast granular cell tumors can also simulate breast cancer on a clinical breast examination because they can be fixed to the skin, and are frequently 'rock hard'. Granular cell breast tumors tend to be slow growing, and solitary, though they occur multiply about 10% of the time. Granular cell tumors, particularly multiple tumors, also tend to be slightly more common in persons with black skin. Granular cell tumors of the breast may occur in both sexes, but they are slighly more common in women.
Histological analysis of granular cell breast tumors typically reveals sheets and nests of polygonal cells. Granular eosinophilic cytoplasm is abundant, and cells usually have distinct borders. The granularity' of these breast tumors is due to an accumulation of secondary lysosomes in the cytoplasm. As a result, granular cell breast tumors will tend to stain positive for the S-100 protein, which also supports the idea that they derive from Schwann cells. (Breast schwannoma and breast neurofibroma also derive mostly from Schwann cells, which are also found in malignant peripheral nerve sheath tumors of the breast.) Immunohistochemical analysis of granular cell breast tumors tends to include reactivity for periodic acid-Schiff, CD68, and S100 and negative reactivity for cytokeratin. Histological features of granular cell breast tumors can resemble apocrine carcinoma of the breast, but a main difference is the absence of mitotic figures in granular cell tumors. Granular cell breast tumors also tend to be negative for estrogen receptivity.
Histological features of granular cell breast tumors which are more suggestive of malignancy include a larger size tumor (greater than 5cm), cellular and nuclear pleomorphism, increased mitotic activity, prominent nucleoli, and the presence of necrosis. (A granular cell tumor which recurrs locally after having been excised would also tend to indicate a malignant situation.) The only truly reliable measure of malignancy in a breast granular cell tumor would be evidence of metastasis. It must be remembered, however, that malignant granular cell breast tumors are very rare, totally less than 2% of all granular cell tumours. Malignancy is most often encountered with 'deep-seated' lesions in older patients, with an average age of 50.
Breast cancer screening mammograms have the advantage of being highly sensitive (showing a suspicious density of mass) but not very specific (giving a clear indication of what the mass or density actually is). Breast granular cell tumors are rare, and mostly benign, but mammographic images tend to be highly suspicious of malignancy. Mammograms tend to show a suspicious, spiculated mass, possibly with infiltrative margins. They can frequently also be microcalcifications associated with granular cell breast tumors, which, depending on their 'pattern', can be highly suggestive of ductal carcinoma in situ. Breast ultrasounds of granular cell breast tumors typically reveal an irregularly defined hypoechoic mass (solid) with posterior shadowing (sometimes called 'dorsal' shadowing.)
Wide local excision tends to be the way that granular cell breast tumors are treated, whether they are malignant or not. They have a tendency to recurr so margins must be wide and completely free of tumor cells. Adjuvant radiation therapy may be given, but typically only if the tumor is malignant. Unfortunately, removal of granular cell breast tumors tends to be a fairy major surgery, because they have a tendency to attach themselves to adjacent muscles and other structures.
Because there is a tendency for local recurrence and the remote posibility of distant metastasis, follow-up is a crucial aspect of treatment and management. The local recurrence rate of benign granular cell breast tumors ranges between 2% and 8%, while the recurrence rate for malignant forms is much higher, at around 35%. Local recurrence is typically rapid, however, usually within 1 year of the original surgery. Distant metastasis of malignant granular cell breast tumors is quite high, at just over 60%. For unknown reasons, recurrence of malignant breast granular cell tumors is much more common for women than for men. However, bear in mind that for benign granular cell breast tumors, surgical excision is usually a complete cure.
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