Discussion

Diagnosis

Benign spindle cell lesion of the breast, consistent with nodular fasciitis.

Discussion

Spindle cell lesions of the breast carry a wide differential diagnostic possibility, that include spindle cell carcinoma, fibromatosis, myofibroblastoma, nodular fasciitis and others. Each of these pathologies have suggestive histologic findings, such as border infiltration characteristic of spindle cell carcinoma and fibromatosis, or erythrocyte extravasation in nodular fasciitis. However, these features are often not pathognomonic for one disease. Thus, definitive diagnosis of these lesions usually requires use of immunohistochemical stains.

Obviously, it is prudent in these cases to rule in or out the possibility of malignant disease. In this case, several immunostains including AE1/ AE3, CK5, and p63 were used to rule out the possibility of spindle cell carcinoma. Beta catenin, a nuclear stain, is helpful in diagnosing fibromatosis (also negative in this case). CD34 positivity would have been indicative of myofibroblastoma. The SMA positivity, along with these negative findings, led to the diagnosis of nodular fasciitis.

Nodular fasciitis is a proliferative lesion of reactive fibroblastic cells arising from the fascia of the subcutaneous tissue. It is commonly found in soft tissues of the extremities and rarely develops in breast. There are only 22 published case reports of nodular fasciitis in the breast. Nodular fasciitis can mimic breast cancer clinically, radiologically, and histopathologically. They are generally small lesions (<3 cm), with no sex predilection, found in the young to middle-aged. However, when found in the uncommon location of the breast, these demographics shift some. Among the 22 case reports of nodular fasciitis of the breast, 20 of the cases were in females and the age range was 15-84 years. The clinical history for nodular fasciitis of the breast is usually rapid onset of a unilateral, small, painless mass. If not excised, these lesions will often spontaneously regress.   

As one can see from this case example, it is important to be able to appropriately distinguish these spindle cell lesions to prevent mistaking a benign lesion for a malignant carcinoma, thus preventing unnecessary worry and overtreatment.

References

Paliogiannis, P. et al. Breast Nodular Fasciitis: A Comprehensive Review. BreastCare, 2016. 11: 270–274.

Schnitt, SJ and Collins, LC. Biopsy Interpretation of the Breast: Second Edition, 2013. p 363-380. Print.

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