RT-PCR assay to detect FGFR3::TACC3 fusions in formalin-fixed, paraffin-embedded glioblastoma samples.

Background: One targeted treatment option for isocitrate dehydrogenase (IDH)-wild-type glioblastoma focuses on tumors with fibroblast growth factor receptor 3::transforming acidic coiled-coil-containing protein 3 (FGFR3::TACC3) fusions. FGFR3::TACC3 fusion detection can be challenging, as targeted RNA next-generation sequencing (NGS) is not routinely performed, and immunohistochemistry is an imperfect surrogate marker. Fusion status can be determined using reverse transcription polymerase chain reaction (RT-PCR) on fresh frozen (FF) material, but sometimes only formalin-fixed, paraffin-embedded (FFPE) tissue is available. Aim: To develop an RT-PCR assay to determine FGFR3::TACC3 status in FFPE glioblastoma samples. Methods: Twelve tissue microarrays with 353 historical glioblastoma samples were immunohistochemically stained for FGFR3. Samples with overexpression of FGFR3 (n = 13) were subjected to FGFR3::TACC3 RT-PCR on FFPE, using 5 primer sets for the detection of 5 common fusion variants. Fusion-negative samples were additionally analyzed with NGS (n = 6), FGFR3 Fluorescence In Situ Hybridization (n = 6), and RNA sequencing (n = 5). Results: Using RT-PCR on FFPE material of the 13 samples with FGFR3 overexpression, we detected an FGFR3::TACC3 fusion in 7 samples, covering 3 different fusion variants. For 5 of these FF was available, and the presence of the fusion was confirmed through RT-PCR on FF. With RNA sequencing, 1 additional sample was found to harbor an FGFR3::TACC3 fusion (variant not covered by current RT-PCR for FFPE). The frequency of FGFR3::TACC3 fusion in this cohort was 9/353 (2.5%). Conclusions: RT-PCR for FGFR3::TACC3 fusions can successfully be performed on FFPE material, with a specificity of 100% and (due to limited primer sets) a sensitivity of 83.3%. This assay allows for the identification of potential targeted treatment options when only formalin-fixed tissue is available.

Molecular tools for the pathologic diagnosis of central nervous system tumors.

Molecular diagnostics currently has a crucial role in neuro-oncological patient care. (Epi)genetic assays testing for point mutations, copy number variations, gene fusions, translocations, and methylation status are of main diagnostic interest in neuro-oncology. Multiple assays have been developed for this purpose, ranging from single gene tests to high-throughput, integrated techniques enabling detection of multiple genetic aberrations in a single workflow. This review describes the nature of the simpler and more complex assays for molecular diagnostics of tumors of the central nervous system and briefly discusses their strengths and weaknesses.

Schwannoma of the Recurrent Laryngeal Nerve: A Rare Entity.

Neurogenic tumors are the most common posterior mediastinal tumors in adults. Schwannomas originating from the recurrent laryngeal nerve are rare. The present study describes a 46-year-old man with a tumor in the left superior mediastinum. Because of the narrow relationship with the aorta and the left pulmonary artery, the tumor was excised by left-sided minithoracotomy. The tumor, a schwannoma, originated from and encased the left recurrent laryngeal nerve. Six months after surgery, the patient was free of recurrence without symptoms other than hoarseness. "Additional imaging by magnetic resonance imaging could raise the probability of a neurogenic origin of the mass, eventually leading to collaboration with the neurosurgeon in this case."