Microsatellite instability (MSI) and tumor mutational burden (TMB, mutations [mut]/Mb) were determined.Statistically significant differences in genomic alterations (GA) of PMNSGCT versus NS included higher TP53 pathway GA (<i>p</i> < .0001), PIK3CA pathway GA (<i>p</i> < .0001), and lower cell-cycle pathway GA (<i>p</i> = .0004).There were no MSI-high PMNSGCT cases.
In the panel with 2 dinucleotide markers, D17250 linked to p53 and D2S123 to hMSH2, detection rates were 89.9 % (71/79) for MSI-H and 80.0 % (76/95) for MSI-L carcinomas, compared to the Bethesda panel.
These results suggest that APC and p53 alterations occur irrespective of microsatellite instability status in non-familial colorectal carcinomas, and that Ki-ras mutation is not involved in MSI high non-familial colorectal carcinoma.
A single missense mutation was detected in an MSI-high tumor that also contained a frameshift microdeletion, and two missense mutations were identified in an MSI-null tumor wild-type for p53. p53 mutations were detected in 5/12 MSI-low tumors (42%) and 12/34 MSI-null tumors (35%).