Background: We designed and evaluated the suitability of three customized microsatellite instability (MSI) panels using a combination of mono- and dinucleotide markers to improve the detection of MSI status in 56 matched normal and gastric cancer specimens.
Methods: An MSI analysis was performed to optimize the panel of microsatellite markers to detect instability using two different microsatellite panels: (1) mononucleotide marker panel consisting of mononucleotide markers BAT25, BAT26, BAT40, BAT-RII, NR21, NR22, NR24, and NR27 and (2) dinucleotide marker panel containing D2S123, D5S346, D17S250, D17S261, D17S520, D18S34, and D18S58. The customized panels consisted of five, seven, or ten markers with two, three, or four mononucleotide markers, respectively, among fifteen MSI markers described above to fulfill the MSI-H and MSI-L definition based on the revised Bethesda Guidelines. The “Proposal5” panel consisted of BAT40, BAT26, D18S34, D2S123, and D17S520. “Proposal-7” consisted of “Proposal-5” with BAT25 and D18S58. “Proposal-10” consisted of “Proposal-7” with NR27, D17S250, and D17S261.
Results: Immunohistochemical staining for MMR protein expressions such as mutL homolog 1 (MLH1) and mutS homolog 2 (MSH2) revealed that among 56 matched specimens, 13 had defective DNA mismatch repair (MMR) proteins and 43 had proficient MMR proteins. Out of thirteen specimens with defective MMR expression, eight specimens (62%, 8/13) were classified as MSI-H with an instability at ≥ 6 markers and five (38%, 5/13) were MSIL with instability at ≤ 5 markers using all fifteen MSI markers. On the other hand, the analytical sensitivity and specificity of all three customized panels to detect MMR-deficient specimens were 92% (12/13) and 100% (43/43), respectively. In comparison, the sensitivity and specificity of the Bethesda and QMR panels were 62% (8/13) and 100% (43/43). All customized panels could represent the detection of MSI-L tumors rather than the Bethesda and the QMR panels.
Conclusions: The increased sensitivity to detect MSI-unstable tumors with customized panels including BAT40 and D18S34 indicates that precise MSI screening to discriminate MSI-H from MSS and MSI-L may be feasible for gastric cancer.