A 58-year-old man presented to the hospital with complaints of exertional shortness of breath that had begun 2 weeks earlier. He had a history of hypertension and chronic obstructive pulmonary disease, but there were no notable findings on physical examination or in laboratory tests. A chest radiograph taken upon admission revealed a mass-like opacity in the left hilar region, although the left hilar vessels were still discernible (Fig. 1A). Further investigation with contrast-enhanced computed tomography (CT) showed a heterogeneously enhancing mass with smooth borders in the anterior (prevascular) mediastinum, and a distinct tubular vascular structure within the mass was noted (Fig. 1B). There was no evidence of mediastinal or hilar lymphadenopathy. The patient underwent a transthoracic needle biopsy, which yielded only fragments of fibrocollagenous tissue and was inadequate for a definitive diagnosis. Consequently, surgical intervention was planned for both diagnostic and therapeutic purposes. The patient underwent resection of the mediastinal tumor and a total thymectomy via sternotomy. The excised specimen was a well-encapsulated, yellowish mass measuring 10×6×6 cm, with areas of hemorrhage and necrosis. Histopathological examination and immunohistochemical staining confirmed the diagnosis of a malignant solitary fibrous tumor (SFT). The patient’s recovery after surgery was smooth, and he was discharged in good clinical condition.

Figure 1. First preoperative chest radiograph showing a mass lesion in the left hilar area (A); chest computed tomography image demonstrating a heterogeneously enhancing mass in the anterior mediastinum (arrow) (B).

The patient was followed up on an outpatient basis at 6-month intervals for 2 years and annually thereafter. Eight years after the initial follow-up, the patient reported a palpable mass on the left side of his back. A 3.5-cm mass with heterogeneous contrast enhancement was detected on chest magnetic resonance imaging (Fig. 2A). The patient underwent surgical excision of the mass in the orthopedics department, which was confirmed to be a metastatic SFT. The patient continued with follow-up care. One year later, a 2-cm, well-defined, round nodule in the superior segment of the left lower lobe was identified on a follow-up chest CT scan (Fig. 2B). The patient underwent wedge resection of the left lower lobe via video-assisted thoracic surgery, and the presence of metastatic SFT was confirmed once more. Four years later, which was 13 years after the initial surgery, the patient presented with swelling in the left neck. A 5.3-cm, well-defined, heterogeneously enhancing mass within the left thyroid gland was revealed on a neck CT scan (Fig. 2C). An ultrasound-guided needle biopsy of the lesion led to a diagnosis of metastatic SFT. The patient then underwent total thyroidectomy in the endocrine surgery department and had an uncomplicated recovery (Fig. 3A). A microscopic examination of the thyroid lesion showed spindle- to pleomorphic-shaped cells arranged in fascicles with a perivascular pattern, mirroring the characteristics of the previous mediastinal lesion (Fig. 3B). Tumor cells from the thyroid lesions also exhibited strong immunopositivity for CD34, STAT-6, and BCL-2 (Fig. 3C–E). Taking into account the clinical and pathological findings, the final diagnosis was a thyroid metastasis originating from the malignant SFT of the mediastinum.

Figure 2. Chest magnetic resonance imaging (left back, arrow) (A), chest computed tomography (CT) (lower lobe of the left lung, arrow) (B), and neck CT (left thyroid gland, arrow) (C) images at 8, 9, and 13 years after surgery, respectively, showing recurrent solitary fibrous tumor.

Figure 3. Gross photograph of the thyroidectomy specimen (A), histopathologic findings of the mass (hematoxylin and eosin staining, ×200) (B), and immunohistochemical staining for CD34 (C), STAT-6 (D), and BCL-2 (E).

The patient remains in outpatient follow-up and has remained tumor-free for 3 years since the thyroid surgery.

The patient provided written informed consent for publication of his clinical details and images.

SFTs are rare neoplasms that originate from mesenchymal cells, most commonly found in the pleura. While the majority of SFTs grow slowly and are benign, they carry a significant risk of metastasis—reported to be between 35%–45%, with even higher rates observed in studies with extended follow-up periods [1]. Malignant SFTs are histologically characterized by high cellularity, nuclear atypia, a mitotic count exceeding 4 mitoses per 10 high-power fields (HPFs), and the presence of necrosis [2]. However, these histological criteria are not absolute predictors of behavior, as metastases can occur even in patients with SFTs that appear benign under the microscope. Given the challenges in prognostication, numerous researchers have investigated and identified various clinical and histological factors that influence outcomes [3,4]. The French Sarcoma Group, in a multicenter cohort study, developed a risk calculator that highlighted key prognostic factors for local recurrence (visceral localization, radiotherapy, and age), metastasis (mitotic count >4/10 HPFs, non-limb tumor localization, and age ≥60 years), and overall survival (age and mitotic count) [4]. Despite these efforts, no clinicopathological factors have yet been found to precisely predict the prognosis for SFTs. Metastases from SFTs most frequently affect the lungs and pleura, but they have also been documented in a range of other organs [3-5]. O’Neill et al. [5] described the metastatic patterns of SFTs, noting that the primary tumor’s location influenced the metastatic sites, with the lungs and pleura being the most common. They also found that patients with extrathoracic SFTs had a higher statistical likelihood of developing metastatic disease compared to those with thoracic SFTs [5]. In a case similar to ours, Ricciuti et al. [6] documented a rare instance of a giant pleural SFT that metastasized to the thyroid gland a year after complete resection. This case underscores the critical role of surgery, even for patients with isolated metastatic disease [6].

Most recurrences or metastases of SFTs occur within 5 years following radical treatment; however, instances of recurrence have been documented even after 10 or 20 years. A recent case report described the successful treatment of a malignant SFT that recurred in the bilateral pleural cavities 17 years after the initial resection of the primary tumor. The treatment involved a staged reoperation, and the authors emphasized that complete, repeated resection of the recurrent tumor is the optimal therapy for improving patient outcomes [7]. Park et al. [8] described a case where 6 surgical resections were carried out for 6 recurrent SFTs over a 24-year period. Based on this experience, the authors advocate for long-term clinical follow-up for all patients with SFTs and endorse repeated complete resections for recurrences of the disease.

Chemotherapy may be considered for cases of dedifferentiated or metastatic SFTs. Park et al. [9] suggested that conventional chemotherapy, such as doxorubicin-based or gemcitabine-based therapy, could be effective in controlling or stabilizing locally advanced and metastatic SFTs. However, the role of chemotherapy has not been clearly established, and its use, including in neoadjuvant and adjuvant treatments, is not standardized. Currently, the treatment of choice for SFT is surgical resection with the aim of complete removal. Recent studies have reported a 10-year overall survival rate of over 70%, and aggressive surgical resection is recommended, even for recurrent lesions [10].

We report our experience with the successful surgical treatment of an SFT that recurred multiple times in the back, lung, and thyroid gland (an exceptionally rare lesion). Our case indicates that SFTs necessitate long-term follow-up exceeding 10 years. Surgical resection, including that of metastatic lesions, is recommended when complete removal is feasible.

Author contributions

Conceptualization: JSY, SYS, KJN. Data curation: JSY. Formal analysis: JSY, HK. Methodology: JSY, SYS, KJN. Project administration: KJN, SGO. Visualization: JSY, KJN, HK. Writing–original draft: all authors. Writing–review & editing: all authors. Final approval of the manuscript: all authors

Conflict of interest

No potential conflict of interest relevant to this article was reported.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.