Controversial issues in soft tissue solitary fibrous tumors: A pathological and molecular review

Abstract

The clinical evolution of solitary fibrous tumor (SFT) remains unclear. Although various clinical, morphological and molecular criteria may indicate increased risk of malignancy, some SFT can still progress despite having a clearly benign appearance. Various risk stratification systems have been proposed, but unfortunately they are not sufficient to precisely determine the malignant potential. In this review, we discuss current knowledge on SFT, focusing on the following controversial issues: (i) the diverse morphologic spectrum: ‘the great simulator;’ (ii) malignant transformation or dedifferentiation; (iii) current risk stratification systems; and (iv) molecular factors associated with clinical evolution. The morphological spectrum of SFT and the list of differential diagnoses continue to expand. Both have increased considerably since the first descriptions of specific molecular alterations. A classification of malignant SFT should not be based on histology alone. The correlation of all pathological and molecular factors is recommended; its inclusion in risk stratification systems may help to improve diagnosis and prognosis.

The many faces of solitary fibrous tumor; diversity of histological features, differential diagnosis and role of molecular studies and surrogate markers in avoiding misdiagnosis and predicting the behavior

“…Medium sized blood vessels with perivascular fibrosis are also commonly seen (Fig. 2c) [17,25]. The background stroma may show focal or diffuse myxoid change (Fig.…”

“…The background stroma may show focal or diffuse myxoid change (Fig. 2d) [25][26][27]. Classic fibrous SFTs are paucicellular tumors composed of spindle shaped cells arranged in short wavy fascicles or haphazardly present against prominent fibrous stroma with cracking artifact and abundant keloid-type collagen (Fig.…”

“…Owing to diversity of histological patterns exhibited by SFT, Machado et al termed SFT "the great simulator" of soft tissue tumors [25]. SFTs often pose diagnostic challenge and integration of clinical, histomorphological, immunohistochemical and molecular features is necessary for establishing correct diagnosis [17].…”

“…In hypercellular SFTs, tumor cells usually acquire round cell morphology and mimic small round cell sarcomas such as Ewing sarcoma (ES), rhabdomyosarcoma and mesenchymal chondrosarcoma (MC) [25]. Due to high incidence of rhabdomyosarcoma in young patients with head and neck tumors, it should be kept in the differential diagnosis.…”

“…Both ES and MC like SFT express CD99. Positivity for NKX2.2 which is a recently introduced sensitive and specific IHC marker for ES and expression of CD34 and STAT6 by SFTs help in reaching the correct diagnosis [21,25].…”