Context. —Myofibroblastoma (MFB) of the breast is an unusual benign tumor that belongs to the family of the “benign spindle cell tumors of the mammary stroma.” The name MFB reflects its cellular composition, comprising mainly stromal cells with fibromyofibroblastic and, less frequently, myoid differentiation. Since the original description, the morphologic spectrum of MFB has been expanded by the recognition of several unusual morphologic variants, such as the cellular, infiltrative, epithelioid, deciduoid-like, lipomatous, collagenized/fibrous, and myxoid variants. Objective. —To review the literature on mammary MFB, discussing the main clinical, radiologic, and pathologic features helpful for diagnosis. Since MFB may show alarming morphologic features, which can lead to a misdiagnosis of malignancy, histologic figures of this tumor, including its more unusual variants, are provided to offer pathologists a practical approach to a correct diagnosis. Histogenesis and pathogenesis of this tumor are also proposed. Data Sources. —Clinicopathologic data on MFB were extracted from all identified articles through PUB Medline– based research. Histologic figures have been taken from the personal archive of the author. Conclusions. —The incidence of MFB diagnosis has increased in recent years, likely due to the mammographic screening. Accordingly, this unusual benign tumor may represent a potential diagnostic pitfall, especially when interpreting fine-needle aspiration and/or needle core biopsy. Pathologists should be aware of the wide morphologic spectrum exhibited by MFB to avoid a misdiagnosis of malignancy.

We reviewed the world literature on solitary fibrous tumors of the central nervous system from August 1996 to July 2011, focusing on both clinicopathological features and diagnostic findings. The anatomical distribution of the 220 cases reported so far reveals that most are intracranial and just over one-fifth are intraspinal. In decreasing frequency, intracranial tumors involve the supratentorial and infratentorial compartments, the pontocerebellar angle, the sellar and parasellar regions, and the cranial nerves. Intraspinal tumors are mainly located in the thoracic and cervical segments. Although most solitary fibrous tumors of the central nervous system are dural based, a small subset presents as subpial, intraparenchymal, intraventricular, or as tumors involving the nerve rootlets with no dural connection. Preoperative imaging and intraoperative findings suggest meningioma, schwannoma or neurofibroma, hemangiopericytoma, or pituitary tumors. Immunohistochemistry is critical to establish a definitive histopathological diagnosis. Vimentin, CD34, BCL2, and CD99 are the most consistently positive markers. The usual histologic type generally behaves in a benign manner if complete removal is achieved. Recurrence is anticipated when resection is subtotal or when the tumor exhibits atypical histology. The proliferative index as assessed by MIB1 labeling is of prognostic significance. Occasionally, tumors featuring conventional morphology may recur, perhaps because of minimal residual disease left behind during surgical extirpation. Rare extracranial metastases and tumor-related deaths are on record. Surgery is the treatment of choice. Stereotactic and external beam radiation therapy may be indicated for postsurgical tumor remnants and for unresectable recurrences. Long-term active surveillance of the patients is mandatory.

Peripheral nerve sheath tumors encompass a wide spectrum of lesions with different biological behavior, including both benign and malignant neoplasms as well as the recent diagnostic category, i.e., “atypical neurofibromatous neoplasm with uncertain biologic potential” to be used only for NF1 patients. Neurofibromas and schwannomas are benign Schwann-cell-derived peripheral nerve sheath tumors arising as isolated lesions or within the context of classical neurofibromatosis or schwannomatoses. Multiple tumors are a hallmark of neurofibromatosis type 1(NF1) and related forms, NF2-related-schwannomatosis (formerly NF2) or SMARCB1/LZTR1-related schwannomatoses. Perineuriomas are benign, mostly sporadic, peripheral nerve sheath tumors that show morphological, immunohistochemical, and ultrastructural features reminiscent of perineurial differentiation. Hybrid tumors exist, with the most common lesions represented by a variable mixture of neurofibromas, schwannomas, and perineuriomas. Conversely, malignant peripheral nerve sheath tumors are soft tissue sarcomas that may arise from a peripheral nerve or a pre-existing neurofibroma, and in about 50% of cases, these tumors are associated with NF1. The present review emphasizes the main clinicopathologic features of each pathological entity, focusing on the diagnostic clues and unusual morphological variants.