Screening for Lynch Syndrome by Immunohistochemistry of Mismatch Repair Proteins: Significance of Indeterminate Result and Correlation With Mutational Studies

Arch Pathol Lab Med. 2019 Oct;143(10):1225-1233. doi: 10.5858/arpa.2018-0201-OA. Epub 2019 Mar 27.

Abstract

Context.—: Immunohistochemical expression of mismatch repair (MMR) protein is a well-accepted method for routine screening for Lynch syndrome with relatively high sensitivity and specificity. Occasionally, however, immunohistochemistry (IHC) can yield an equivocal result with poor reproducibility and the potential for misdiagnosis.

Objective.—: To determine the frequency and significance of indeterminate MMR IHC expression in patients routinely screened for Lynch syndrome and correlation with germline mutation studies.

Design.—: Semiquantitative scoring of MMR IHC was performed by image analysis in 479 cases, of which 380 were colorectal and 99 endometrial cancer. Scores of 10% or more, less than 10%, and 0% were used as cutoffs for retained, indeterminate, and loss of expression, respectively. Negative and indeterminate IHC results were confirmed by mutational studies.

Results.—: Four hundred eighteen of 479 cases (87.2%) were reported as retained expression, 45 (9.3%) as loss of expression, and 16 (3.3%) as indeterminate expression. Fifteen of 45 (33.3%) and 8 of 16 (50%) with loss and indeterminate expression, respectively, were found to have Lynch syndrome by germline studies. The overall frequency of Lynch syndrome in our patient population was 4.8% (23 of 479), and 34.7% of these (8 of 23) were associated with indeterminate IHC expression. In the indeterminate group, MLH1 germline mutation was the most frequent (6 of 13; 46.2%), followed by MSH6 (4 of 13; 30.7%).

Conclusions.—: Our findings provide further evidence that indeterminate IHC should be further investigated for possible MMR germline mutation. Guidelines for interpretation of MMR IHC and the establishment of more objective criteria for defining indeterminate results are important to improve the sensitivity and specificity of the IHC assay.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Colorectal Neoplasms, Hereditary Nonpolyposis / diagnosis*
  • Colorectal Neoplasms, Hereditary Nonpolyposis / genetics
  • Colorectal Neoplasms, Hereditary Nonpolyposis / pathology
  • DNA Mismatch Repair*
  • DNA Mutational Analysis
  • DNA-Binding Proteins / genetics*
  • Female
  • Germ-Line Mutation
  • Humans
  • Immunohistochemistry
  • Male
  • Middle Aged
  • MutL Protein Homolog 1 / genetics*
  • Prospective Studies
  • Reproducibility of Results
  • Retrospective Studies

Substances

  • DNA-Binding Proteins
  • G-T mismatch-binding protein
  • MLH1 protein, human
  • MutL Protein Homolog 1