Table 1 Classification of unusual MMR-D tumors according to MMR IHC profiles and MSI status.

From: An unusual phenotype occurs in 15% of mismatch repair-deficient tumors and is associated with non-colorectal cancers and genetic syndromes

IHC\MSI

Group 1

Group 2

Group 3

Group 4

 

Isolated loss of PMS2 or MSH6

Classical loss of PMS2/MLH1 or MSH2/MSH6

MLH1/PMS2/ MSH2/MSH6 retained

Other types of MMR protein loss

All

MSI-high

43

Classical MMR-D

3

13

59

MSI-low

1

8

2

0

11

MSS

9

8

MMR-P

2

19

All

53

16

5

15

89

  1. Tumors were sub-divided into four groups according to the IHC staining and MSI-PCR results. Group 1: isolated loss of PMS2 or MSH6 (with MSI-High, MSI-Low or MSS). Group 2: classical loss of PMS2/MLH1 or MSH2/MSH6 heterodimers (with MSI-Low or MSS, but not MSI-High since these cases correspond to classical MMR-D tumors). Group 3: retained staining of the four MMR proteins (with MSI-H or MSI-L but not MSS since these cases correspond to MMR-P tumors). Group 4: another type of MMR protein loss (with MSI-High, MSI-Low or MSS).
  2. MMR-D mismatch repair-deficient tumor, MMR-P mismatch repair-proficient tumor, IHC immunohistochemistry, MSI microsatellite instability, MSI-High: instability of 2 or more microsatellites, MSI-Low: only one unstable microsatellite, MSS: stability of the 5 microsatellites.
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