Utility of p16 immunohistochemistry for the identification of Lynch syndrome.
OBJECTIVE
Immunohistochemistry for mismatch repair proteins has shown utility in the identification of Lynch syndrome, but majority of tumors with loss of MLH1 expression are due to sporadic hypermethylation of the MLH1 promoter. These tumors can also show epigenetic silencing of other genes, such as p16. The aim of our study is to evaluate the utility of p16 immunohistochemistry in the prediction of MLH1 germline mutations.


METHODS
p16 immunohistochemistry was appropriately evaluated in 79 colorectal cancers with loss of MLH1 expression. Methylation of MLH1 and p16 were quantitatively studied using real-time PCR assay Methylight. BRAF V600E mutation in tumor tissue was also investigated. Genetic testing for germline mutation of MLH1 was made on 52 patients.


RESULTS
Loss of p16 expression was seen in 21 of 79 samples (26.6%). There was found statistically significant association between p16 expression and p16 methylation (P < 0.001), MLH1 methylation (P < 0.001), and BRAF mutation (P < 0.005). All tumors with loss of p16 expression showed hypermethylation of p16 (21 of 21), 95.2% (20 of 21) showed MLH1 methylation, and 71.4% (15 of 21) were mutated for BRAF V600E. Mutational analysis showed pathogenic germline mutations in 8 of the patients, harboring 10 tumors. All 10 of these tumors showed normal staining of p16 in the immunochemical analysis.


CONCLUSIONS
p16 immunohistochemistry is a good surrogate marker for p16 and MLH1 epigenetic silencing due to hypermethylation, and is useful as screening tool in the selection of patients for genetic testing in Lynch syndrome.
Payá
Artemio
A
Unidad de Investigación, Hospital General Universitario de Alicante, Alicante, Spain.
Alenda
Cristina
C
Pérez-Carbonell
Lucía
L
Rojas
Estefanía
E
Soto
José-Luis
JL
Guillén
Carmen
C
Castillejo
Adela
A
Barberá
Victor M
VM
Carrato
Alfredo
A
Castells
Antoni
A
Llor
Xavier
X
Andreu
Montserrat
M
Koh
Jim
J
Enders
Greg H
GH
Benlloch
Susana
S
Jover
Rodrigo
R
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000235:genetics / Q000378:metabolism*; D019941:Cyclin-Dependent Kinase Inhibitor p16; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005260:Female; D018095:Germ-Line Mutation / Q000235:genetics; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics; D011379:Prognosis; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; C000614131:CDKN2A protein, human; D019941:Cyclin-Dependent Kinase Inhibitor p16; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D000070957:MutL Protein Homolog 1