Examples of unexpected protein expression in colorectal cancers with pathogenic mismatch repair gene mutation. (A-B) Lynch syndrome with germline MSH6 missense mutation (case #3), showing intact MSH6 and MSH2 staining; (C-D) Lynch syndrome with germline MSH6 missense mutation (case #4), showing retained but weaker than control MSH6 staining in 30% tumor, MSH2 staining is intact; (E-F) Lynch syndrome with germline MLH1 truncating mutation (case #5), showing intact MLH1 staining, but weaker than control PMS2 staining in 5% tumor; (G-H) Lynch syndrome with germline MSH6 truncating mutation (case #7), showing intact MSH6 and MSH2 staining; (I-J) Sporadic colorectal cancer with double somatic MLH1 mutations (case #10), showing weaker than control MLH1 staining in 10% tumor and loss of PMS2 expression. WTC: weaker than internal control. MMR, mismatch repair Original magnification: 400x.