Solitary Fibrous Tumor of the Breast

A solitary fibrous tumor is one of a group of similar breast neoplasms which develop mostly from ‘stromal‘ cells and tissues, and not from glandular or epithelial cells.

Sometimes the name ‘solitary fibrous tumor‘ is used as an over-arching term for all the different variations of these tumors (such as myofibroblastoma and leiomyoma).

However, the name also generally refers to a specific tumor-type which lacks some of the distinguishing features of the others.

This group of benign fibrous-stromal tumors accounts for less than 0.2% of all breast lesions, and are just as common in men as in women.

Fibroblasts and myofibroblasts

The essential, unifying feature of this particular group of breast lesions are the neoplastic cells that have a characteristic ‘spindle‘ shape.

These spindle-like cells are mesenchymal cells (genetically immature, undifferentiated cells, or ‘stem‘ cells). Furthermore, these cells will tend to be either

fibroblasts: a somewhat undifferentiated cell likely to become connective tissue or
myofibroblasts (a somewhat undifferentiated cell likely to become smooth muscle tissue) or
something in-between

So, medics may refer to the ‘solitary fibrous tumor’ as a specific type of lesion.

This is a tumor whereby the ‘immature connective tissue cells’, or fibroblasts, are the most prominent. In addition, the tumor may lack any other striking differential features.

I just want to let you know that this page is from around the year 2000, so it’s pretty old. Therefore, we have created a newer version with more up-to-date information on Solitary Fibrous Tumors.

Solitary fibrous tumors can not confidently be distinguished from breast cancer by radiology alone, so histological evaluation is required (excisional biopsy).

By microscopic appearance, solitary fibrous breast tumors, and most stromal tumors, are well-circumscribed lesions.

The bland, spindle-like fibroblastic cells form into short fascicles or clusters with a mixture of collagen. In rare instances, a certain amount of adipose tissue (fat cells) may also be present in the tumor.

Tumors stain highly for desmin

Solitary fibrous tumors will test positive for secretions of the proteins CD34, Bcl2, CD99, and vimentin. But, they test very strongly for desmin, and do not test positive for smooth muscle actin, and these histological nuances more-or-less define this particular type of breast lesion.

Is a solitary fibrous breast tumor a concern for breast cancer or increased risk?

Solitary fibrous tumors and related stromal neoplasms are a bit hard to categorize. In general, specialists do not consider solitray fibrous tumors to be breast cancer.

In fact, the main concern with a finding of an apparent solitary fibrous tumor is to arrive at a proper differential diagnosis, because the ‘spindle-like‘ cells can take mimic spindle cell breast carcinoma.

So, a diagnosis of solitary fibrous tumor and not spindle cell breast cancer is very good news.

Most solitary fibrous tumors of the breast are benign

On the whole, solitary fibrous breast tumors are benign, but they are not entirely benign. One of the things the pathologist will look for are ‘atypical‘ cellular features, and the more atypical the cells are, the more likely that there may be malignant aspects to the lesions down the road.

Some of these lesions have been known to recur locally or even to metastasize and depending upon where they metastasize, there could be problems and future treatments required.

However, it should be emphasized that a solitary fibrous breast tumor is a neoplasm involving unusual, but otherwise normal, cells.

They can grow and cause problems, but they do not ‘devour and destroy‘ the way breast cancer cells do.

Treatment of breast solitary fibrous tumors

Solitary fibrous breast tumors are typically treated by extensive surgical resection (lumpectomy).

There is no evidence that chemotherapy or radiation treatments are either necessary or effective.

Breast specialists will follow-up this condition routinely. Even though the disease generally has a non-aggressive clinical course, the possibility of local recurrence and unlikely metastasis does merit strict follow-up observation, particularly if there are any atypical features.

References

Bombonati A, Parra JS, Schwartz GF, Palazzo JP: Solitary fibrous tumor of the breast. Breast J 2003, 9:251.
Nielsen GP, O’Connell JX, Dickersin GR, Rosenberg AE. Solitary fibrous tumor of soft tissue: a report of 15 cases, including 5 malignant examples
with light microscopic, immunohistochemical, and ultrastructural data. Mod Pathol. 1997;10:1028–1037.
Salomao, DR., Crotty, TB., Nascimento, AG., Myofibroblastoma and solitary fibrous tumour of the breast: histopathologic and immunohistochemical studies.
The Breast Volume 10, Issue 1, February 2001, Pages 49-54
Abd El All, HS., Breast spindle cell tumours: about eight cases. Diagnostic Pathology 2006, 1:13
Damiani S, Miettinen M, Peterse JL, Eusebi V: Solitary fibrous tumour (myofibroblastoma) of the breast.Virchows Arch 1994, 425:89-92.