Quality assessment and correlation of microsatellite instability and immunohistochemical markers among population- and clinic-based colorectal tumors results from the Colon Cancer Family Registry

Abstract

The detection of defective mismatch repair (MMR), as assessed by the presence of tumor microsatellite instability (MSI) and/or loss of MMR protein expression by IHC, has been useful for risk assessment, prognosis, and prediction of treatment in patients with colorectal cancer. We analyzed tumors for the presence of defective MMR from 5927 Colorectal Cancer Family Registry patients recruited at six international consortium sites. We evaluated the appropriate percentage instability cutoff used to distinguish the three MSI phenotypes [ie, stable (MSS), low instability (MSI-L), and high instability (MSI-H)]; the sensitivity, specificity, and performance characteristics of individual markers; and the concordance between MSI and IHC phenotypes. Guided by the results of the IHC testing, our findings indicate that the distinction between an MSI-H phenotype from a low-instability or MSS phenotype can best be accomplished by using a cutoff of 30% or greater of the markers showing instability. The sensitivity and specificity of the mononucleotide markers were higher than those of the dinucleotide markers. Specifically, BAT26 and BAT25 had the highest sensitivity (94%) and specificity (98%), and the use of mononucleotide markers alone identified 97% of the MSI-H cases correctly. As expected, the presence of MSI-H correlated with an older age of diagnosis, the presence of tumor in the proximal colon, and female sex.

Figure 1

Distribution of cases with complete presence (no loss) or loss of expression in any of the four proteins (ie, MLH1, MSH2, MSH6, and/or PMS2) by IHC within percentage MSI phenotypes: population-based cases (n = 3824) (A) and clinic-based cases (n = 658) (B).

Figure 2

MSI marker panel percentage instability by IHC status among MLH1/PMS2 loss cases (A), MSH2/MSH6 loss cases (B), PMS2 loss-only cases (C), and MSH6 loss-only cases (D). Only cases with IHC codes zero and four are included in the analysis. MSI codes one, two, and six through nine are defined as interpretable. Percentage instability is calculated by dividing the number of unstable cases with the all-interpretable cases for each MSI marker. Loss of expression case counts in parentheses are total numbers and not specific to individual MSI marker interpretable data points. Pop. indicates population.

Figure 3

Individual marker percentage MSI: MSI-L cases (A) and MSI-H cases (B). The sensitivity and specificity of each marker in identifying MMR protein deficiency are also given. All CFR cases (C). Pop. indicates population.

Figure 4

Distribution of equivocal (A) and no amplification (B) calls for each of the 10 markers among the 4482 cases with available data on a minimum four MSI markers. Among equivocal and no amplification calls, the frequencies are shown for each of the three MSI phenotypes (ie, MSS, MSI-L, and MSI-H) and the total.