[546] Usefulness of p16 Immunohistochemistry in the Diagnosis of Lynch's Syndrome
C Alenda, A Paya, L Perez, E Alcaraz, JL Soto, C Guillen, V Barbera, A Carrato, A Castillejo, R Jover. University General Hospital, Alicante, Spain; University General Hospital, Elche, Spain; AEG, Spain, Spain
Background: MLH1 inactivation may be observed in sporadic and Lynch's syndrome colorectal carcinoma (CRC). Lynch syndrome is caused by germline mutations in the mismatch repair genes. Sporadic CRC is caused by epigenetic silencing of MLH1, because of its promoter methylation. These tumours are due to hypermethylation of multiple genetic locus, one of them, CDKN2A (p16). The aim of this study is to evaluate the value of p16 immunohistochemistry in the prediction of germline MLH1 mutation in patients with CRC that show loss of MLH1 expression.
Design: The study was performed in 89 tumours with loss of MLH1 immunohistochemical expression from patients of the Genetic Counselling in Cancer Department of HGUE and from a series of non-selected surgical CRC specimens from the EPICOLON study and the Pathology Department of the HGUA. Immunohistochemical analysis for p16 was performed on tissue microarray. The MLH1 and CDKN2A (p16) methylation analysis was performed by Methylight. BRAF V600E mutation was detected using specific TaqMan probes by real time PCR. In 54 tumours, mutation analysis of MLH1 was performed.
Results: Loss of p16 expression was seen in 21 out of 76 valuable samples (27.5%). All tumours with loss of p16 expression showed hypermethylation of p16 (21/21, p<0.001), 95.2% (20/21, p<0.005) showed MLH1 methylation and 66.7% (14/21, p<0.005) were mutated for BRAF V600E. Values of diferent strategies for detecting Lynch Syndrome are shown.
Strategies for detecting Lynch syndrome | Sensivity | Specifity | PPV | NPV | OR |
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| P16 IHC | 25 | 100 | 100 | 32 | 1.5 (1.1-1.8) | | BRAF V600E | 29 | 100 | 100 | 43 | 1.8 (1.4-2.3) | | MLH1meth | 53 | 100 | 100 | 80 | 4.9 (2.7-8.8) | | Bethesda | 32 | 100 | 100 | 52 | 2.1 (1.5-2.9) | | P16 IHC + BRAF + Bethesda + MLH1meth | 63 | 100 | 100 | 86 | 7.3 (3.5-15.4) | IHC: immunohistochemistry, meth: methylation S: sensivity, Sp: specifity, PPV: positive predictive value, NPV: negative predictive value, OR: odds ratio
Conclusions: p16 immunohistochemistry is a good surrogate marker for CDKN2A (p16) and MLH1 epigenetic silencing due to hypermethylation, and could be useful as a screening tool in the selection of patients for genetic testing in Lynch syndrome. The use of this technique could avoid germline testing in approximately a third of patients with loss of MLH1 expression.
Category: Gastrointestinal
Monday, March 9, 2009 1:00 PM
Poster Session II # 68, Monday Afternoon
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