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June 2020 — Neuropathology

A 25-month-old female presented with eye deviation and ataxia and was found to have a large mass filling the fourth ventricle. The tumor was resected, and histopathological analysis showed a solid and papillary pattern of growth with poor differentiation, high mitotic activity, and areas of necrosis (Figure 1). The tumor also showed diffuse CAM5.2 immunostain, focal synaptophysin positivity, lacked expression of glial markers GFAP and Olig2, and showed loss of INI-1 and largely of H3 K27me3 expression. Overall, the tumor resembled a choroid plexus carcinoma. Tumor purity was morphologically estimated as 70%. Molecular and cytogenetic analyses were performed at the Mayo Clinic Genomics Laboratory. Neuro-oncology NGS testing showed a SMARCB1 mutation involving a canonical splice site in 84% of all sequencing reads (c.986+2T>G) (Figure 2). Chromosomal microarray identified losses along chromosomes 11 (including genes NUP98, IGF2, H19, and CDKN1C), 22 (including genes SMARCB1, MN1, NF2, EWSR1, and CHEK2), and X (Figure 3).

Image 1A.
Image 1B.
Image 1C.
Histological features of the tumor. Images 1A-1C) The tumor presents a solid and papillary pattern of growth. It is composed of cells with high NC ratio, poorly differentiated either in sheets or lining the cores of the papillae, and high mitotic activity with areas of necrosis.
Image 2A. Molecular analysis of SMARCB1. The position of the mutation is shown in between blue lines, as well as the nucleotide substitution (G).
Image 2B. Molecular analysis of SMARCB1. Effect of the mutation on transcript splicing, notice how the canonical 5’ splicing sequence is disrupted in the mutated sequence compared to the reference (blue squares).
Image 3.

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Photo of Cinthya Jeanette Zepeda Mendoza, Ph.D. Cinthya Jeanette Zepeda Mendoza, Ph.D.
Fellow, Laboratory Genetics and Genomics
Mayo Clinic
Photo of Kandelaria (Ande) Rumilla, M.D. Kandelaria (Ande) Rumilla, M.D.
Consultant, Laboratory Genetics and Genomics
Mayo Clinic
Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science
Photo of Caterina Giannini, M.D., Ph.D. Caterina Giannini, M.D., Ph.D.
Consultant, Anatomic Pathology
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science
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