Guided by these metabolic hotspots, a repeat biopsy of the tumor periphery confirmed sheets of undifferentiated malignant cells with rhabdoid morphology (Figure 3A, H&E), showing loss of BRG1 immunohistochemical stain (Figure 3C), diffuse Ki67 index of 70% (Figure 3B), and pan-cytokeratin expression (PCK+, Figure 3D), establishing the diagnosis of SMARCA4-deficient undifferentiated tumor. Here, SMARCA4 is linked to neoplasm.