PMC5999866_01
Pathologic analysis of tumor tissue: (a) H&E staining of neoplastic cells display the typical primitive small round blue cell appearance. Rare cells have eccentric nuclei and eosinophilic cytoplasm characteristic of rhabdoid morphology. (b): By SMARCB1/INI-1 immunohistochemical staining, the tumor cells demonstrate a loss of nuclear immunoreactivity; endothelial, stromal, and inflammatory cells retain normal nuclear staining.
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Pathological evaluation of tumor tissue and immunohistochemistry (IHC) showed complete loss of SMARCB1 expression, consistent with biallelic inactivation of SMARCB1 and a diagnosis of AT/RT (see Fig. 1). We hypothesized that mitotic instability of r(22) led to somatic, mosaic monosomy chromosome 22, followed by a second-hit that resulted in SMARCB1 loss of function (Figure 1b).
Chromosomal microarray comparing normal control to (a) peripheral blood and (b) patient tumor. Plot (c) compares the patient's peripheral blood to tumor. Patient tumor and blood samples confirm a 3.1-Mb terminal deletion, 22q13.3q13.3, consistent with the patient's known diagnosis of Phelan-McDermid syndrome. Mosaic monosomy 22 is seen in tumor tissue but absent in peripheral blood (b and c).
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Clara, CA). Chromosomal microarray results of blood confirmed a heterozygous 3.1-Mb terminal deletion at 22q13.1q13.3, consistent with the patient's known diagnosis of Phelan-McDermid syndrome (Fig. 2a). Hybridization of tumor to blood revealed loss of the proximal 48-Mb of chromosome 22 in tumor, consistent with loss of the r(22) (Figure 2c).