Fibrous tumors involving the mammary gland are uncommon and account for less than 0.2% of all primary breast lesions, without a striking difference of incidence between male and female as for ductal epithelial cancers [1
]. The majority of cases described in the literature occurred in the thoracic cavity, but various sites, including head and neck [2
], liver [3
], skin [4
], soft tissue [5
] and meninges [7
], were recognized. Extraserosal solitary fibrous tumor can be included in the group of benign spindle stromal tumors of the breast, which encompasses a spectrum of lesions sharing several basic common clinical, morphological, and immunohistochemical analogies [9
]. Tumors with similar features have been reported in the literature with different names, frequently used interchangeably, creating confusion of terminology among pathologists and clinicians. The unifying morphological criterion of all these lesions is represented by a well-circumscribed proliferation of bland-looking spindly to oval-epithelioid cells forming short fascicles and/or clusters, admixed with thick or thin collagen bands. Recently, Magro et al. proposed to subdivide these tumors in two main groups: the fibroblastic and myofibroblastic types (2002). Although both categories have a basic common immunophenotype characterized by immunoreactivity for vimentin, CD34, Bcl2 and CD99, they differentiate for the expression of myogenic markers including α-smooth muscle actin and desmin, lacking in the former and strongly expressed in the latter one [9
]. Main morphological features of mesenchymal lesions of the breast are described in table .
Main morphological features of mesenchymal lesions of the breast
The interest of the present case relies on its rarity and in the difficulties to achieve the exact diagnosis, because this tumor has no typical radiological features and cytological aspects cannot frequently solve the diagnostic doubts between benign and malignant lesion. Tumors appear as single nodules, generally with well defined borders and enter in differential diagnosis with other more common lesions, including fibroadenomas and fillodes tumors. Moreover, breast cancer cannot be ruled out on the basis of radiological features. Cytology can help in the differential diagnosis from breast cancer, but could not in differentiating from other mixed epithelial-mesenchymal tumors. For all these reasons, the exact diagnosis is frequently achieved after surgical resection, that also has a curative purpose. Histologically, differential diagnosis of solitary fibrous tumors includes a wide variety of other benign and malignant bland-looking monomorphic spindle cell lesions of the breast, including nodular fascitis, inflammatory myofibroblastic tumor, fibromatosis, benign peripheral nerve sheet tumors, haemangiopericytomas and leiomyomas [10
]. The differential diagnosis includes breast myofibroblastoma that shows the same morphological features, but differentiates for the expression of muscle-related antigens such as actin and desmin [9
]. For this reason immunohistochemistry is a main tool in order to reach a correct diagnosis. However, the two entities have substantially the same clinical and biological behavior. Furthermore, differential diagnosis of a breast mass in a male routinely must distinguish from gynecomastia, which remains the most common cause of either unilateral or bilateral breast mass, frequently associated to hormonal therapy. Although more commonly bilateral and symmetric with well-defined discoid margins, histopatologic confirmation is the only sure differential between benign and malignant disease.
The differential diagnosis from cancer is the most important issue due to the very different prognostic implication. Although in surgical specimen this differential diagnosis is generally easy, on small bioptic or cytological specimens it may be difficult. In particular the detection in such preparations of epithelioid cells arranged in Indian files may mimic an infiltrating lobular carcinoma. Immunohistochemistry showing negativity for epithelial markers helps in excluding the presence of a breast cancer.
The treatment of choice for solitary fibrous tumours is extensive surgical resection. Up to now there is no evidence that chemotherapy and radiation are effective. The local recurrence or onset of metastases mainly depends on histological parameters. Although most solitary fibrous tumours are characterized by a non-aggressive clinical course, some can recur locally or display malignant behaviour, so a strict and long-term follow-up is recommended mainly for atypical forms.