Scrotum solitary fibrous tumor

Background: A solitary fibrous tumor (SFT) is a rare clinical tumor, often manifesting as solitary nodules. It is a rare condition that occurs in the scrotum. Currently, no study has reported this condition. Case summary: We reported a case of an SFT in a 77-year-old man, and discuss its diagnosis, differential diagnosis, and treatment. Clinical and histopathological features, as well as the EnVision 2-stepmethod, were used to diagnosis the SFT. The results of imaging tests and surgery indicated that the SFT was located in the right scrotum with 2 connected tumor nodules and a clear perimeter. The larger one was 11.0cm 9.3cm 8.1cm, and the smaller one was 3.1cm 2.0cm 2.0cm. Pathological results indicated that in both tumor nodules, tumor cells were spindle-shaped with unclear cell boundaries. The nucleus was vacuolated with mild to moderate atypia. In the larger tumor nodule, there were many thin-walled blood vessels with vasodilation or branching. In the smaller tumor nodule, rich blood vessels were found, mostly with fibrous degeneration of the thick walls of blood vessels, and more collagen-like tissue in the interstitial layers. Immunohistochemical results demonstrated diffuse, strongly positive expression of CD34, CD99, Vim, and Bcl-2markers. The expression of the new fusion gene, NAB2–STAT6, as an alternative tool specifically confirmed the diagnosis of SFT. This patient underwent lump resection without further treatment. The patient is alive after 18-month follow-up. Conclusion: This case was diagnosed as a SFT according to its histopathological features, immunophenotype. The patient is still alive at 18 months follow-up after the lump resection. Abbreviations: CD10 = cluster of differentiation 10, CD21 = cluster of differentiation 21, CD34 = cluster of differentiation 34, CD35 = cluster of differentiation 35, CD68 = cluster of differentiation 68, CD99 = cluster of differentiation 99, CD117 = cluster of differentiation 117, CDFI = color Doppler flow imaging, CR = calretinin, EMA = epithelial membrane antigen, HMB45 = Melanoma Marker Antibody, Ki-67 = Ki-67 protein, MC =mesothelial cell, MRI =magnetic resonance imaging, NAB2 = NGFI-A binding protein 2, SFT= solitary fibrous tumor, SMA= smooth muscle actin, STAT6= activator of transcription 6, T1= T1-weighted scans, T2= T2weighted scans, T2WI = T2-weighted image.