Sporadic Solid/Cystic Hemangioblastomas in the Cerebellum: Retrospective Study of More Than Ten Years of Experience in a Single Center

Identifying Tumor Microenvironment Biomarkers in Adherent and Cystic Vestibular Schwannomas

OBJECTIVE

A subset of vestibular schwannomas (VSs), including cystic tumors, have higher postoperative morbidity because of the presence of adhesions between the tumor, facial nerve (FN), and brainstem. We identify tumor microenvironment (TME) biomarkers to better classify these tumors and predict the degree of tumor adherence.

STUDY DESIGN

Retrospective case series.

SETTING

Tertiary skull base referral center.

METHODS

Adult patients with cystic and solid VS matched in tumor size who underwent surgical resection were included. Expressions of seven biomarkers of extracellular matrix remodeling and tumor immune response were quantified via immunohistochemistry. The distribution of CD45+ immune cells was evaluated in intratumoral and perivascular compartments. The degree of tumor adherence was categorized as none, adherent to FN, or adherent to both FN and brainstem.

RESULTS

Twenty-eight patients were included. Cystic VSs were significantly more adherent than solid VSs ( p = 0.02). Patients with adherent VS had shorter duration of symptoms and were more likely to undergo subtotal resection. In solid tumors, matrix metalloproteinase (MMP)-2 expression ( p = 0.02) and CD163+ macrophage infiltration ( p = 0.007) were correlated with tumor size. Linear discriminant analyses (LDAs) demonstrated MMP-2, MMP-14, CD80, CD163, and perivascular CD45 to be individually predictive of the degree of tumor adherence (all p < 0.05), with perivascular CD45 being the best independent predictor ( p = 0.005). An LDA model including these biomarkers demonstrated 100% accurate discrimination of all three levels of tumor adherence ( p = 0.04).

CONCLUSIONS

Adherent VS have a distinct proinflammatory TME characterized by elevated MMP expression, enrichment of tumor-associated macrophages, and perivascular immune cell infiltration.

Reliable detection of genetic alterations in cyst fluid DNA for the diagnosis of brain tumors

PURPOSE

Liquid biopsy of cyst fluid in brain tumors has not been extensively studied to date. The present study was performed to see whether diagnostic genetic alterations found in brain tumor tissue DNA could also be detected in cell-free DNA (cfDNA) of cyst fluid in cystic brain tumors.

METHODS

Cyst fluid was obtained from 22 patients undergoing surgery for a cystic brain tumor with confirmed genetic alterations in tumor DNA. Pathological diagnoses based on WHO 2021 classification and diagnostic alterations in the tumor DNA, such as IDH1 R132H and TERT promoter mutation for oligodendrogliomas, were detected by Sanger sequencing. The same alterations were analyzed by both droplet digital PCR (ddPCR) and Sanger sequencing in cyst fluid cfDNA. Additionally, multiplex ligation-dependent probe amplification (MLPA) assays were performed to assess 1p/19q status, presence of CDKN2A loss, PTEN loss and EGFR amplification, to assess whether differentiating between astrocytomas and oligodendrogliomas and grading is possible from cyst fluid cfDNA.

RESULTS

Twenty-five genetic alterations were found in 22 tumor samples. All (100%) alterations were detected in cyst fluid cfDNA by ddPCR. Twenty of the 25 (80%) alterations were also detected by Sanger sequencing of cyst fluid cfDNA. Variant allele frequency (VAF) in cyst fluid cfDNA was comparable to that of tumor DNA (R = 0.62, Pearson's correlation). MLPA was feasible in 11 out of 17 (65%) diffuse gliomas, with close correlation of results between tumor DNA and cyst fluid cfDNA.

CONCLUSION

Cell-free DNA obtained from cyst fluid in cystic brain tumors is a reliable alternative to tumor DNA when diagnosing brain tumors.