Solitary Fibrous Tumor: A 10-Year Retrospective Analysis with Several Rare Cases
Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms first described in the pleura but later identified in diverse extrapleural sites, including the peritoneum, lung, head/neck, orbit, and central nervous system. Despite their widespread recognition, their rarity limits comprehensive understanding of their epidemiology, clinical behavior, and prognostic factors. This retrospective study of 262 SFT patients treated at a single institution over a decade provides critical insights into the demographics, clinical characteristics, treatment outcomes, and rare presentations of SFTs, alongside an analysis of diagnostic challenges and management strategies.
Epidemiology and Clinical Characteristics
The cohort comprised 262 patients, including 199 inpatients (76.0%), with a slight female predominance (51.9%). The median age at diagnosis was 46.6 ± 15.4 years (range: 3 months–76 years), with 94.3% of patients over 18 years old. Notably, a 3-month-old infant represented the youngest reported SFT case in medical literature. Tumors arose predominantly in the pleura (21.8%), lung (20.2%), head/neck (13.7%), and extremities (9.9%). Less common sites included the retroperitoneum (7.6%), abdomen (5.3%), pelvis (5.0%), and central nervous system (5.0%). Rare locations such as the breast, pericardium, groin, and trunk/skin collectively accounted for 6.9% of cases.
Symptomatology varied by tumor location. Pleural, mediastinal, and pulmonary tumors were often asymptomatic and detected incidentally during routine exams. Palpable masses were the primary complaint in abdominal, extremity, and groin tumors, while pelvic and retroperitoneal tumors caused localized swelling or pain. Central nervous system SFTs frequently presented with dizziness or focal pain. Tumor size correlated with anatomic site: head/neck, CNS, lung, and extremity tumors were typically <5 cm, whereas mediastinal, pelvic, and trunk/skin lesions measured 5.1–9.9 cm. Pleural, abdominal, retroperitoneal, and groin tumors often exceeded 10 cm (Supplementary Table 2).
Pathological Classification and Treatment Outcomes
Histopathological analysis classified 87.8% (n=230) of tumors as benign and 12.2% (n=32) as malignant, with malignancy rates varying across sites. Surgical resection was performed in 93.5% of inpatients (n=186), while 6.3% (n=13) underwent diagnostic needle biopsy. Adjuvant therapies included chemotherapy in 2.5% (n=5) and radiotherapy in 2.0% (n=4). Recurrence occurred in 7.0% of surgically treated patients (n=14), emphasizing the importance of long-term surveillance even for benign-appearing lesions.
Rare Case Presentations and Diagnostic Insights
Breast SFTs
Two rare breast SFTs were documented. The first case involved a 56-year-old woman with a 2-year history of a left breast nodule. Mammography revealed an ovoid, lobulated mass with peripheral calcifications (Supplementary Figure 1B). Histology showed a spindle cell tumor with minimal atypia (<3 mitoses/10 HPF) and fibrocollagenous stroma (Figure 1A). Immunohistochemistry confirmed STAT6 and CD34 positivity, consistent with intermediate SFT. The patient remained recurrence-free after resection at 1-year follow-up.
The second breast case involved a 66-year-old man with a rapidly growing left breast mass. Ultrasound demonstrated a 3.6 cm hypoechoic lesion with hypervascularity (Figure 1D). Core biopsy revealed a hypocellular spindle cell tumor without atypia (Figure 1C), classified as benign. Observation was chosen, and the patient remained stable over 18 months.
Pericardial SFT
A 68-year-old man presented with dyspnea and chest tightness. MRI identified a heterogeneous T2 hyperintense mass adjacent to the left ventricle (Figure 1F). Partial resection revealed a hypercellular tumor with marked nuclear atypia, >10 mitoses/10 HPF, and hemorrhage (Figure 1E), indicative of aggressive SFT. The patient was lost to follow-up post-discharge, highlighting challenges in managing advanced cases.
Inguinal SFTs
Two groin SFTs illustrated biologic variability. A benign case in a 46-year-old man featured a well-circumscribed mass with hyalinized vessels and chondroid metaplasia (Figure 1G). Wide excision achieved cure, with no recurrence. In contrast, a malignant case in a 42-year-old man showed infiltrative growth, marked atypia, and high mitotic activity (Figure 1H). Despite adjuvant radiotherapy, local recurrence at 9 months necessitated repeat surgery and radiation. The patient remained disease-free at 12 months.
Therapeutic Considerations and Prognostic Factors
Complete surgical excision remains the cornerstone of SFT management. However, the study underscores that benign histology does not preclude recurrence, necessitating long-term follow-up. Adjuvant radiotherapy may reduce recurrence in marginal resections or high-risk lesions. While chemotherapy’s role remains undefined, targeted therapies (e.g., antiangiogenic agents) show promise in recurrent or metastatic disease.
Tumor size, location, and mitotic activity were key prognostic indicators. Large tumors in anatomically expansive regions (e.g., retroperitoneum) often presented late, complicating resection. Mitotic counts >4/10 HPF, necrosis, and infiltrative margins correlated with malignant behavior.
Diagnostic Challenges
Preoperative differentiation of SFTs from other mesenchymal tumors (e.g., fibromatosis, fibrosarcoma) relies on immunohistochemistry (CD34, STAT6, BCL2 positivity) and molecular testing for NAB2-STAT6 fusion, a pathognomonic genetic alteration. Radiologic features vary by site but often include well-circumscribed margins and heterogeneous enhancement on MRI.
Study Limitations
This retrospective analysis has limitations. Outpatient data incompleteness restricted detailed clinical histories for some cases. Pathologic review, though performed by two experienced pathologists, was not blinded, potentially introducing bias. Additionally, follow-up duration varied, warranting further longitudinal studies.
Conclusion
This 10-year retrospective study elucidates the clinicopathologic spectrum of SFTs, emphasizing their diagnostic complexity and variable biologic behavior. Rare presentations in the breast, pericardium, and groin highlight the need for heightened clinical suspicion in atypical locations. Comprehensive surgical excision, coupled with vigilant follow-up, remains critical for optimizing outcomes. The inclusion of the youngest reported SFT patient expands the epidemiologic understanding of this enigmatic neoplasm.
doi:10.1097/CM9.0000000000001170
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