Detection of VHL deletion by fluorescence in situ hybridization in extraneuraxial hemangioblastoma of soft tissue

Recurrent Tuberous Sclerosis Complex/Mammalian Target of Rapamycin Mutations Define Primary Renal Hemangioblastoma as a Unique Entity Distinct From Its Central Nervous System Counterpart

ABSTRACT

Renal hemangioblastoma (HB) is a rare subset of HBs arising outside of the central nervous system (CNS), with its molecular drivers remaining entirely unknown. There were no significant alterations detected in previous studies, including von Hippel-Lindau gene alterations, which are commonly associated with CNS-HB. This study aimed to determine the real molecular identity of renal HB and better understand its relationship with CNS-HB. A cohort of 10 renal HBs was submitted for next-generation sequencing technology. As a control, 5 classic CNS-HBs were similarly analyzed. Based on the molecular results, glycoprotein nonmetastatic B (GPNMB) immunohistochemistry was further performed in the cases of renal HB and CNS-HB. Mutational analysis demonstrated that all 10 renal HBs harbored somatic mutations in tuberous sclerosis complex 1 ( TSC1 , 5 cases), TSC2 (3 cases), and mammalian target of rapamycin (2 cases), with the majority classified as pathogenic or likely pathogenic. The CNS-HB cohort uniformly demonstrated somatic mutations in the von Hippel-Lindau gene. GPNMB was strong and diffuse in all 10 renal HBs and completely negative in CNS-HBs, reinforcing the molecular findings. Our study reveals a specific molecular hallmark in renal HB, characterized by recurrent TSC/mammalian target of rapamycin mutations, which defines it as a unique entity distinct from CNS-HB. This molecular finding potentially expands the therapeutic options for patients with renal HB. GPNMB can be considered for inclusion in immunohistochemical panels to improve renal HB identification.

Recurrent YAP1-TFE3 Gene Fusions in Clear Cell Stromal Tumor of the Lung

Clear cell (hemangioblastoma-like) stromal tumor of the lung (CCST-L) is a recently described distinctive rare pulmonary neoplasm of unknown histogenesis and molecular pathogenesis. Only 7 cases have been reported in 2 recent studies, although additional cases might have been reported under the heading of extraneural pulmonary hemangioblastoma. We herein describe 4 CCST-L cases, 3 of them harboring a YAP1-TFE3 fusion. The fusion-positive tumors occurred in 3 women, aged 29, 56, and 69 years. All presented with solitary lung nodules measuring 2.3 to 9.5 cm. Histologically, all tumors showed similar features being composed of relatively uniform medium-sized epithelioid to ovoid cells with clear cytoplasm and small round monomorphic nuclei. Scattered larger cells with enlarged hyperchromatic nuclei and marked pleomorphism were noted in 2 cases. The tumors were associated with a hypervascularized stroma with variable but essentially subtle resemblance to capillary hemangioblastoma and perivascular epithelioid cell tumor (PEComa). Immunohistochemistry was negative for all lineage-specific markers. Targeted RNA sequencing showed a YAP1-TFE3 fusion in 3 of 4 cases. All 3 tumors showed homogeneous nuclear TFE3 immunoreactivity. Two patients were disease free at 36 and 12 months. The third patient had biopsy-proven synchronous renal and hepatic metastases, but extended follow-up is not available (recent case). The fourth case lacking the fusion affected a 66-year-old woman and showed subtle histologic differences from the fusion-positive cases, but had comparable TFE3 immunoreactivity. CCST-L represents a distinctive entity unrelated to hemangioblastoma and likely driven by recurrent YAP1-TFE3 fusions in most cases. The relationship of our cases to the recently reported "hemangioblastoma-like" CCST-L remains to be determined. Analysis of larger series is paramount to delineate the morphologic spectrum and biological behavior of this poorly characterized entity.