A large right chest mass is seen in this CT scan. The mass occupies most of the hemithorax. The mediastinum shows some deviation as do the aorta and vena cava, but no evidence of invasion is seen.
This is a cross section of an encapsulated brown-red solid tumor with bands of fibrosis. These tumors often arise on a pedicle, which makes for easy resectability and hence, favorable prognosis.
Variable collagen deposition laid in parallel to spindle cells is a distinctive feature of SFT.
Another image showing variable cellularity due to the amount of collagen.
The spindle cell areas can exhibit a variety of patterns and in this instance, demonstrates prominent hemangiopericytoma-like vessels with a loose edematous background.
Here is another example showing a more spindled appearance with vague fasicular growth.
This wedge shaped lesion is well-circumscribed and partially covered by pleura. The stroma appears whorled.
One can see where the lesion emanates from the lung parenchyma (bottom).
The collagen has a keloidal appearance.
CD34 positivity is a hallmark of this lesion.
As is bcl-2 positivity throughout the tumor. Insulin-like growth factor also stains positively in the spindle cells.
This tumor is also on the list of CD99 positive lesions.
Beta-catenin is also positive in the spindle cells.
Solitary fibrous tumor (SFT) is the most common mesenchymal neoplasm of the pleura (Fletcher, Zander). In contrast to mesothelioma, SFT does not have features of mesothelial cells and there is no association with asbestos exposure.
Note that SFT can occur in a variety of locations, including within the lung (intrapulmonary SFT). Some experts consider SFT the benign counterpart in a spectrum of tumors which includes fibrosarcoma (intermediate differentiation) and malignant fibrous histiocytoma (poorly differentiated)(Fletcher).
Grossly, most SFTs arise from the visceral pleura and are attached by a pedicle. Firm and rubbery in texture, the cut surface is gray-white and whorled.
Microscopically, two key components are seen: (1) fascicles of spindle cells and (2) stromal sclerosis. A characteristic feature is the formation of ropy strands of keloidal collagen parallel to the spindle cell fibers. The transition between cellular and acellular areas can be abrupt, and the spindled areas may exhibit storiform, fascicular, hemangiopericytic or "patternless" patterns of growth. Nuclear features are usually bland.
High cellularity, mitoses greater than 4 MF per 10 HPF, prominent pleomorphism and necrosis may be seen in clinically indolent tumors or alternatively, absent in infiltrative tumors. Thus, these histologic features may not have predictable value unless found in unresectable tumors, in which case, they may suggest aggressive behavior.
SFT is consistently positive for vimentin, CD34 (80% of SFT), bcl-2 and CD99 and negative for keratin, EMA, actin, desmin and S-100 (Fletcher). IHC studies will be invaluable in distinguishing SFT from other entities on the differential such as sarcomatoid or desmoplastic mesothelioma, monophasic synovial sarcoma and desmoid tumor (Zander).
Often affect patients in late middle age (50s and 60s) with no gender predilection -- cases in all ages have been described.
Usually asymptomatic at presentation, but hypertrophic pulmonary osteoarthropathy is an unusual symptom of SFT, found in up to 22% of patients, especially in tumors >7 cm(Briselli). Hypertrophic pulmonary osteoarthropathy is characterized by clubbing of digits and periostosis of long bones of the extremities. This painful condition can be primary, or more commonly secondary to systemic conditions such as pulmonary or cardiac disease.
Significant hypoglycemia may also be found in approximately 4% of cases, and is attributed to the production of insulin-like growth factors by the tumor cells. This finding is reported more in women (Zander).
Complete surgical resection is recommended, with 1 to 2 cm margins if possible. These tumors do not appear to respond to chemotherapy and/or radiation.
The best prognostic factor is completeness of resection. Most often benign SFT is able to be resected completely, with no recurrence (Cardillo). However, occasional recurrences of benign tumors have been reported in some studies (England).
→Two unusual clinical presentations associated with SFT are hypertrophic pulmonary osteoarthropathy and hypoglycemia.
Briselli M, Mark EJ, Dickersin GR (1981) Solitary fibrous tumors of the pleura: eight new cases and review of 360 cases in the literature. Cancer 47:2678–2689
Cardillo G, Facciolo F, Cavazzana AO et al (2000) Localized (solitary) fibrous tumors of the pleura: an analysis of 55 patients. Ann Thorac Surg 70:1808–181
England DM, Hochholzer L, McCarthy MJ (1989) Localized benign and malignant fibrous tumors of the pleura. A clinicopathologic review of 223 cases. Am J Surg Pathol 13:640–658
Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 208-9.
Zander DS, Farver CF. Pulmonary Pathology: Foundations in Diagnostic Pathology. Philadelphia, PA: Elvesier; 2008: 703-6.