Exploring Solitary Fibrous Tumors at a Tertiary Cancer Center: Clinicopathological and Immunomorphologic Profile

Abstract

Background Solitary fibrous tumor (SFT) is a distinct fibroblastic tumor that can occur at any anatomical site and can manifest a variety of histopathological features. NAB2-STAT6 gene fusion has recently emerged as a sensitive and specific molecular marker and its surrogate on immunohistochemistry, STAT6 has also displayed considerable efficacy. Nevertheless, its histologic diversity can result in diagnostic challenges, especially when classic features are not apparent. Methods A retrospective study was conducted at a tertiary cancer centre in North India over 3 years to document the clinicopathologic and immunomorphologic profile of SFTs. Immunohistochemical analysis of BCOR and p53 were gauged additionally and patients were stratified according to Modified Demicco and Salas criteria for risk of metastasis. Results Sixteen patients of SFT were identified, affecting middle-aged men and women equally. Though lung/pleura are known to be involved commonly, SFT affects other sites such as the kidney, brain, buccal mucosa, liver, and penis as well. The majority endured localized disease while a lesser number suffered locoregional/distant spread. Two patients revealed features of a malignant profile. Risk stratification according to the Modified Demicco and Salas criteria evinced comparable results. No discernible relationship however was highlighted between the immunohistochemical expression of BCOR, p53, and any significant SFT parameter. Conclusion Although SFTs are very rare substantially benign mesenchymal neoplasms, pathologists must be conversant with their histological diversity and be vigilant of their malignant attributes. The worth of STAT6 immunohistochemistry for precise diagnosis and long-term studies for delineating clinical behavior cannot be overemphasized.

Keywords: bcor; demicco; p53; risk assessment; salas; solitary fibrous tumors; stat6.

Figure 1. Penile mass

a. Penile lesion, encapsulated and bossellated mass measuring 10x4.5x4 cm. b. hematoxylin and eosin (H&E) stain (100x) showing hypo and hypercellular areas with few staghorn-shaped vessels c. H&E stain (400x) demonstrates ovoid to spindle cells with homogenous-looking nuclei d. STAT6 immunohistochemistry (IHC) (100x) shows diffuse nuclear positive staining e. p53 IHC (100x) shows strong nuclear positive staining in nearly 70% of tumor cells f. BCOR IHC (100x) is negative.

Figure 2. Solitary fibrous tumor of the kidney

a. Gross image of kidney mass, homogenous in appearance, soft to firm in consistency b. hematoxylin and eosin (H&E) (40x) showing hypo and hypercellular areas. Native renal parenchyma is not seen. c. H&E (100x) shows haphazardly arranged spindle cells with bland nuclei d. STAT6 immunohistochemistry (IHC) (100x) shows diffuse nuclear positive staining e. BCOR IHC (100x), and f. p53 IHC (100x) are respectively negative.

Figure 3. A case of solitary fibrous tumor of the lung

a. Hematoxylin and eosin (H&E) (100x) showing spindle cells arranged haphazardly with a single hemangiopericytomatous (HPC)-like vessel, b. STAT6 immunohistochemistry (IHC)(100x) showing diffuse strong nuclear positive staining, c. Tumor cells are positive for CD34 IHC (100x) and d. BCL2 IHC (100x)

Figure 4. A case of malignant solitary fibrous tumor of the distal extremity

a. Hematoxylin and eosin (H&E) (400x), Highly pleomorphic nuclei, with atypical mitotic figures highlighted by arrows b. STAT6 immunohistochemistry (IHC) (100x) diffuse nuclear positive c. BCOR IHC (100x) was negative (score 0) d. p53 IHC (100x) was negative (score 0).