New Observations on a Low-Grade Diffusely Infiltrative Tumour, SMARCB1 Mutant, Arguing for a New Tumour Type.

Two new cases of low-grade diffusely infiltrative tumour (LGDIT), SMARCB1 mutant, are described in an 18-year-old and a 50-year-old male, both with supratentorial lesions, characteristic rhabdoid histology on a myxoid-collagenous background, and complete INI1 loss. Both tumours showed homozygous SMARCB1 deletion and clustered with previously reported LGDIT on t-SNE analysis, in proximity to ATRT-MYC. These observations reinforce the distinct clinicopathological profile of LGDIT and support its consideration as a provisional CNS tumour type.