Malignant transformation of low-grade diffusely infiltrative tumor (LGDIT), SMARCB1-mutant to atypical teratoid/rhabdoid tumor (AT/RT).

We present a rare case of low-grade diffusely infiltrative tumor (LGDIT), SMARCB1-mutant, recurred as an atypical teratoid/rhabdoid tumor (AT/RT) seven years after complete resection. Comprehensive genetic and epigenetic analysis of both LGDIT, SMARCB1-mutant, and AT/RT samples revealed that SMARCB1 mutation and methylation patterns are stable during the latent period and not the direct target that determines the malignant phenotype of cancer. However, there was a switch of oncogenic signaling pathways from the MAPK pathway to the PI3K/AKT pathway with accumulation of somatic variants responsible for the inherent malignant phenotype. Considering the dormant oncogenic traits behind an innocent phenotype, it is recommended to confirm the diagnosis of LGDIT, SMARCB1-mutant, by conducting a methylation classifier analysis or an SMARCB1 expression study to ensure accurate prognosis prediction.