World J Surg. 2013 Oct;37(10):2468-75. doi: 10.1007/s00268-013-2134-2.

MISMATCH REPAIR DEFICIENCY SCREENING VIA IMMUNOHISTOCHEMICAL STAINING IN YOUNG ASIAN COLORECTAL CANCERS.

Min-Hoe, Chew1; Poh-Koon, Koh1; Melinda, Tan2; Kiat-Hon, Lim3; Loi Carol1; Choong-Leong, Tang1

1 Department of Colorectal Surgery, Singapore General Hospital

2 Duke-NUS Graduate Medical School, Singapore

3 Department of Pathology, Singapore General Hospital, Singapore

 

ABSTRACT:

Background: The incidence of mismatch repair (MMR) deficiency in young CRC remains unknown in Asians. This study assessed the clinicopathological features and efficacy of immunohistochemistry (IHC) screening for Lynch Syndrome (LS) in young Asian CRC patients.

Methods: From January 2006 to December 2010, patients under the age of 50 with IHC staining for MMR proteins in resected CRC specimens were retrieved from a prospective computerized database.

Results: 240 unrelated patients comprising predominantly 82% Chinese (n = 196), with median age of diagnosis at 44 years (range 22 – 50 years) had IHC performed. 22% (n=51) of the patients had abnormal IHC staining. Loss of staining for MLH1, MSH2, MSH6 and PMS2 proteins were observed in 10%, 4%, 6% and 13% of tumors respectively. Of the 22 patients who had abnormal staining of MLH1, thirteen had concomitant abnormal staining for PMS2. One tumour specimen had abnormal staining in all four proteins. However if Amsterdam criteria alone were to be used, 86% (n=14) of the cohort would have not been detected for possible MMR gene defects.

Conclusion: The overall probable burden of germline MMR deficiency in the Singapore population may be as high as 22%. Amsterdam criteria alone is inadequate to detect LS related patients. The use of IHC staining of at least four MMR proteins is a useful screening strategy for LS diagnosis and routine screening of mismatch repair deficiency may be recommended for all young Asian CRC patients.

Keywords: Immunohistochemistry, HNPCC, Asian, Young colorectal cancers

PMID: 23887594

 

SUPPLEMENT:

Lynch Syndrome (LS) is the most common of the hereditary colorectal cancers syndromes with an incidence of 1%-5% of all colorectal cancers (CRC). Patients with LS phenotypically have early-onset colorectal or endometrial cancer, and have distinctive features histologically; resulting from autosomal dominantly inherited germline mutations in the DNA mismatch repair (MMR) genes. The most common mutations involve primarily MLH1 or MSH2. The diagnosis of LS is important in screening for both colon and extra-colonic cancers. Family members are also at high-risk of inheriting LS, and deaths in LS patients can be prevented with early diagnosis and appropriate screening. Defective mismatch repair leads to expansion or contraction of short repeated sequences of DNA, a phenomenon known as microsatellite instability (MSI). More than 80% of tumours from patients with LS display MSI. Mutations in the MMR genes lead to loss of immunohistochemical (IHC) staining of their protein products and this has been used as a phenotypic marker of an underlying mutation in the MMR genes. Determining the MSI status of a tumour requires micro-dissection and polymerase chain reaction-based techniques that are more laborious and costly, requiring the expertise of a molecular laboratory. In contrast, IHC staining only requires standard equipment and expertise for immuno-staining that are available in most pathology departments. This may provide a cost effective means of screening for LS syndrome, where absence of staining for one or more MMR proteins identifies possible gene mutations in a given family.

Our study reports a consecutive series of 240 unrelated young CRC patients (≤50 years old), for whom IHC staining was performed. This is the first study examining the use of IHC staining of MMR proteins for Lynch Syndrome (LS) screening in an unselected cohort of young Asian colorectal cancer patients. Traditionally, clinical criteria such as the Amsterdam I/II and Bethesda criteria have been established to guide further gene testing in the diagnosis of Lynch syndrome. While these guidelines are useful tools, the limited sensitivity and specificity of these criteria are well established. These criteria have been based on Caucasian studies and may not be appropriate when applied to an Asian population as phenotypic, molecular and histopathological features may vary between different ethnic groups. Routine MSI testing in familial and sporadic CRC is expensive, labour intensive, requires expert pathologic examination, microdissection and amplification of a panel of genetic markers. Although it has become cheaper and easier to perform and is a highly sensitive indicator of defective mismatch repair, it needs to be complemented by germline testing for the offending MMR gene defect in cases of MSI-H and would require genetic counseling of affected individuals. Such services may not be widely available. At present, it remains unclear whether any one set of criteria can be applied uniformly to distinct populations likely to have different genetic and environmental risks. IHC is increasingly replacing MSI as a screening method for deficient MMR. While both tests have similar sensitivities (80-91%) and specificities (88-90.2%), IHC is cheaper and convenient with little added facilities required and are thus more cost-effective. One additional advantage is that the MMR gene that is likely to be mutated can be pinpointed as well through a loss of protein staining.

We found that amongst the 51 cases with abnormal IHC staining, only seven patients (14%) fulfilled Amsterdam Criteria. 86% (n=44) of the cohort would therefore have not been detected for mismatch repair gene defects. Nonetheless, despite the limited sample size in this study, it appears that at least a substantial portion (22%) of our young CRC cases may be MMR-deficient and possibly LS related. This study also highlighted the difficulty of using family history alone as a tool in screening for LS. In Singapore, we observed a tendency towards smaller family sizes. Furthermore, the largely migrant population with limited genealogical data meant that collection of accurate data concerning a family’s cancer history is often difficult and unreliable. As a result, routine IHC screening may be a more effective and reliable strategy in all patients with young CRC in Singapore to improve our detection of LS.

We have shown in this series that the use of IHC staining of MMR proteins is a possible screening strategy for LS diagnosis in a cohort of unselected young Asian CRC patients. MMR deficiency by IHC is noted in up to 21% of young CRCs. This allows identification of cases young CRCs that will require more in-depth germline mutation studies. The use of Amsterdam criteria for selection of cases for screening may also not be suitable in an Asian population. We await long term data on the significance of MMR deficient cancers but suggest routine screening of mismatch repair deficiency for all young Asian CRC patients.

Contact Information

Dr Min Hoe, Chew
Consultant Surgeon
Department of Colorectal Surgery
Singapore General Hospital
Level 5, The Academia, 20 College Road
Singapore 169608
Email: chew.min.hoe@sgh.com.sg

MLH1-negative Exampled of MLH1 negative on IHC staining

MSH2 Example of MSH2 negative on IHC staining

 

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