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Washington University Experience | NEOPLASMS (GLIAL) | PLNTY | 2S Case 2 Denouement
Dénouement: We now have considered the possibility of this tumor representing a 'polymorphous low grade neuroepithelial tumor of the young' (PLNTY) given the combined features of bland 'oligodendroglia-like' tumor phenotype, BRAF alteration by FISH and immunohistochemistry, and aberrant expression of CD34. The current tumor, notably, lacks the 'oligodendroglioma-like' appearance and is, in fact, now harboring frequent nucleoli, focally brisk mitotic activity, and moderate to regionally marked pleomorphism; presence of the latter two findings suggests malignant transformation and favors a high-grade designation even though robust evidence for microvascular proliferation and/or necrosis is lacking in this limited biopsy. Targeted next-generation sequencing on the current tumor has revealed variants in PIK3R1R577del, BCORL1 K171fs*82, TERTp (146C>T) and CDKN2A/B loss with a tumor mutational burden of 3 mutations per megabase. These genomic alterations, specifically CDKN2A/B loss and TERTp mutation, furthermore hint towards an aggressive clinical behavior. Even though we favored the current tumor to represent a malignant transformation of PLNTY, it remains somewhat debatable at this time because of the rarity of such occurrence with only a single case report available in the literature (Bale TA et al. Malignant transformation of a polymorphous low grade neuroepithelial tumor of the young (PLNTY). Acta Neuropathol. 2021 Jan;141(1):123-125) ---- A FISH study for BRAF rearrangement at Cincinnati Children’s Hospital showed that 26.5% of tumor cells have 3 copies of BRAF and 18% have four copies of BRAF (7q34). There is no balanced rearrangement or a tandem duplication of 3’BRAF. Methylation-specific PCR shows MGMT gene promoter methylation is absent. ---- We sent the current tumor as well as his prior 2019 tumor to the NIH for methylation profiling. The 2 samples for this case clustered together and are nearby other PLNTY samples rather than other higher grade neoplasms.
