Solitary Fibrous Tumor of the Adrenal Gland.

ABSTRACT

OBJECTIVES: Solitary fibrous tumor (SFT) is a mesenchymal neoplasm that can arise at various anatomic locations. It is characterized by inv12(q13q13)-derived NAB2STAT6 fusion, resulting in the nuclear expression of STAT6. Primary SFT of the adrenal gland is rare. We launched a multi-institutional collaboration to comprehend the overarching demographics, clinical and follow-up, macroscopic, microscopic, IHC, and FISH features of 9 patients with SFT of the adrenal gland. METHODS: We added a series of 9 patients to the collection of adrenal SFTs where the clinicopathologic parameters, including clinical presentation, imaging, histopathology, IHC, molecular profiles, and management and follow-up data, were analyzed comprehensively. A modified 4-variable risk stratification model, including age, tumor size, and necrosis, was applied. RESULTS: Our series consisted of 6 male and 3 female patients, ranging in age from 19 to 64 years (mean, 49.3 years). Abdominal pain (4) and fever with abdominal pain (1) were the presenting symptoms in 5 patients. In the remaining 4 patients, the tumors were detected by abdominal imaging for hypertension and diabetes. The size of the tumor ranged from 2 cm to 10.5 cm in maximum dimension. All tumors exhibited the morphology of a spindle cell SFT with a patternless architecture; 3 had a focal storiform arrangement. STAT6 positivity was observed in all tumors, and 7 were positive for CD34. Surgical resection was the primary modality of treatment. No adjuvant therapy was administered. Follow-up ranging from 7 months to 23 months was available for 7 patients. All were alive without disease recurrence or metastasis. Risk stratification placed 8 (88.9%) patients into a low-risk category and 1 into an intermediate-risk category. CONCLUSIONS: This series is the largest of adrenal SFTs to date. These tumors of the adrenal gland are predominantly spindle cell neoplasms with indolent behavior, with a wide age distribution and a slight male preponderance. Combining our cohort with the previously published cases, the majority of tumors fall into the low-risk category for the propensity to develop metastases. Owing to the rarity and age distribution associated with these tumors, the differential diagnosis is wide and requires a systematic approach for ruling out key differential diagnoses aided by STAT6 IHC.