This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Whitehall, V. L. J. Articles by Jass, J. R. Search for Related Content PubMed PubMed Citation Articles by Whitehall, V. L. J. Articles by Jass, J. R.

Methylation of O–6-Methylguanine DNA Methyltransferase Characterizes a Subset of Colorectal Cancer with Low-level DNA Microsatellite Instability¹

Conjoint Gastroenterology Laboratory, Royal Brisbane Hospital Foundation, Clinical Research Centre [V. L. J. W., J. Y., B. A. L.], and Department of Pathology, University of Queensland [M. D. W., J. R. J.], Brisbane, Queensland, Australia

	ABSTRACT

Top ABSTRACT Introduction Materials and Methods Results Discussion REFERENCES

 
The significance of low-level DNA microsatellite instability (MSI-L) is not well understood. K-ras mutation is associated with MSI-L colorectal cancer and with the silencing of the DNA repair gene O–6-methylguanine DNA methyltransferase (MGMT) by methylation of its promoter region. MGMT methylation was studied in sporadic colorectal cancers stratified as DNA microsatellite instability-high (n = 23), MSI-L (n = 44), and microsatellite-stable (n = 23). Methylation-specific PCR was used to detect MGMT-promoter hypermethylation in 3 of 23 (13%) microsatellite instability-high, in 28 of 44 (64%) MSI-L, and in 6 of 23 (26%) microsatellite-stable cancers (P = 0.0001). K-ras was mutated in 20 of 29 (69%) methylated MSI-L cancers and in 2 of 15 (13%) unmethylated MSI-L cancers (P = 0.001), indicating a relationship between MGMT-methylation and mutation of K-ras. Loss of nuclear expression of MGMT was demonstrated immunohistochemically in 23 of 31 (74%) cancers with methylated MGMT and in 10 of 49 (20%) cancers with nonmethylated MGMT (P < 0.0001). Loss of expression of MGMT was also demonstrated in 9 of 31 serrated polyps. Silencing of MGMT may predispose to mutation by overwhelming the DNA mismatch repair system and occurs with greatest frequency in MSI-L colorectal cancers.

	Introduction

Top ABSTRACT Introduction Materials and Methods Results Discussion REFERENCES

 
Classifying colorectal cancer on the basis of the presence or absence of mutational bandshifts in microsatellite loci has highlighted two major molecular pathways. The MSI³ -positive pathway proceeds with little evidence of loss of heterozygosity, whereas MSS or MSI-negative cancers show a loss of classical tumor suppressor loci. These have been described as "mutator" and "suppressor" pathways, respectively (1) .

When a series of colorectal cancers is studied with a panel of markers for the detection of MSI, MSI tumors are distributed bimodally with a breakpoint at around 30% (2 , 3) . A National Cancer Institute workshop recommended the use of five microsatellite markers (BAT25, BAT26, D5S346, D2S123, and D17S250) to distinguish MSI-H cancers with instability at two or more loci from MSI-L cancers with instability at one locus (4) . It was accepted that additional markers would be required to separate MSS and cancers with a low frequency of bandshifts, but it was also noted that MSS and MSI-L cancers were phenotypically similar (4) .

There is evidence that MSI-L status has biological significance in colorectal neoplasia, but also that MSI-L lesions may be heterogeneous. A low level of MSI is associated with cancers from individuals with germline mutation of hMSH6 (5) . Instability at mononucleotide markers including BAT25 and BAT26 is relatively common in cancers from subjects with hMSH6 germline mutation (6) . By contrast, instability in BAT25, BAT26 and BAT40 was not observed in sporadic MSI-L cancers, which instead implicated markers with di-, tri-, tetra-, and pentanucleotide repeats (2) . Similar patterns of microsatellite marker sensitivities have been described in MSI-L polyps including hyperplastic polyps, mixed polyps and serrated adenomas (serrated polyps; Refs. 7, 8, 9 ), and in MSI-L adenomas from subjects with hereditary nonpolyposis colorectal cancer (10) . In serrated polyps, MSI-L is not associated with the loss of expression of hMLH1 or hMSH2 (8) , whereas MSI-L adenomas in hereditary nonpolyposis colorectal cancer show a loss of expression congruent with the germline mutation (10) .

A feature distinguishing MSI-L and MSI-H colorectal cancers is the high frequency of K-ras mutation in the former (11) . Interestingly, the frequency of K-ras mutation appears to be higher in MSI-L than MSS cancers (11) . K-ras mutation has also been documented in microscopic foci of hyperplasia known as ACF (12) . Hyperplastic ACF may enlarge to become hyperplastic polyps, and a small number may convert to adenoma when still of microscopic size (13) . ACF may also show MSI (14) and aberrant gene methylation (15) . The demonstration of K-ras mutation and MSI within a particular class of microscopic lesion suggests that the changes are related and may represent early steps in the evolution of MSI-L cancer. This suggestion fits with descriptions of a serrated neoplastic pathway (7) .

The DNA repair gene MGMT removes mutagenic adducts from the 0⁶ position of guanine (16) . Inactivation of MGMT is associated with genetic mutation in colorectal neoplasms, particularly G to A transitions in K-ras (17) . MGMT inactivation occurs through promoter hypermethylation and has been demonstrated in small colorectal adenomas (18) . This provides a mechanism to explain both K-ras mutation and low-level MSI. The latter would arise not by inactivation of a DNA mismatch repair gene but by overloading the DNA mismatch repair system. If these premises were correct, one would expect to observe a high frequency of MGMT methylation in the MSI-L subset of colorectal cancers and in precursor lesions.

	Materials and Methods

Top ABSTRACT Introduction Materials and Methods Results Discussion REFERENCES

 
Ninety paired normal and tumor samples were obtained in a fresh state from colorectal cancers resected at the Royal Brisbane Hospital between 1989 and 2000. All patients provided informed consent. Cancers were classified according to the level of MSI using a panel of markers recommended by a National Cancer Institute workshop (BAT25, BAT26, D5S346, D2S123, and D17S250; Ref. 4 ) using methods described previously (11) . Two or more positive loci indicated a MSI-H tumor, one indicated MSI-L, and no positive markers indicated MSS (4) . The compound marker MYCL was also included, but cancers remained classified as MSI-L if bandshifts occurred in MYCL, a single dinucleotide marker, and no mononucleotide markers. The MSI-enriched series included 23 MSI-H, 44 MSI-L, and 23 MSS cancers. No additional criteria were applied to select tumors within MSI subclasses. Six MSI-L cancers were additional to an earlier reported series (11) .

Establishment of the methylation status of the MGMT gene used six CpG sites in the promoter region and used methylation-specific PCR (18) . This sensitive technique is based on the premise that unmethylated cytosines in bisulfite-modified genomic DNA are converted to uracil bases, whereas methylated cytosines are preserved. The region of interest is then amplified with primers specific to either the methylated DNA or to the modified and unmethylated DNA. The PCR product (10 µl) was visualized on a 10% nondenaturing polyacrylamide gel stained with ethidium bromide. Additional assay details have been published previously (18 , 19) .

Mutation of the K-ras oncogene was assayed at the two most common "hot spots" for mutation: codons 12 and 13. A modified RFLP approach was adopted (20) . Briefly, mismatched primers were used to amplify a 157-bp PCR product that resisted restriction enzyme digestion with BstN1 (New England Biolabs) if a mutation was present in codon 12 or with BglI if a mutation was present in codon 13. Putative mutations were confirmed by manual sequencing using an Ampli-Cycle cycle sequencing kit (Perkin-Elmer).

Formalin fixed, paraffin-embedded cancer tissues (that corresponded with the fresh tissue samples used for assessing methylation of MGMT) were obtained from the files of the Royal Brisbane Hospital Pathology Department. Sections were also prepared from 31 serrated polyps (hyperplastic polyps, mixed polyps, and serrated adenomas) of known DNA microsatellite status. These were either sporadic lesions (7) or had presented in subjects with hyperplastic polyposis (8) or hereditary nonpolyposis colorectal cancer (10) . Paraffin sections were affixed to Superfrost Plus adhesive slides (Menzel-Gläser, Braunschweig, Germany). After dewaxing and rehydration to distilled water, the sections were subject to heat antigen retrieval in 0.001 M EDTA (pH 8). Endogenous peroxidase activity sections were blocked using 1.0% H₂O₂, 0.1% NaN₃ in TBS [0.05 M Tris and 0.15 M NaCl (pH 7.2–7.4)]. After transfer to a humidified chamber, the sections were incubated with 10% normal (nonimmune) goat serum (Zymed Corp., San Francisco, CA). The sections were incubated overnight with mouse anti-MGMT monoclonal antibody (clone MT3.1; NeoMarkers, Fremont, CA) diluted 1:125 in TBS. After washing in TBS, biotin-like activity was blocked using the Biotin Blocking Kit (Dako Corp., Carpinteria, CA). The sections were subsequently incubated with biotinylated goat antimouse immunoglobulins (Jackson ImmunoResearch, West Grove, PA) at 1:400 dilution and then with streptavidin-horseradish peroxidase conjugate (Jackson ImmunoResearch) diluted 1:600. Color was developed in 3,3'-diaminobenzidine (Sigma Chemical Co., St. Louis, MO) with H₂O₂ as substrate. Normal epithelium and stromal cells provided a positive internal control. Statistical significance was identified using the two-sided Fisher’s exact test or Pearson’s ² when one or more sample number(s) in any one comparison fell below a sample size of n = 5.

	Results

Top ABSTRACT Introduction Materials and Methods Results Discussion REFERENCES

 
Methylation of MGMT was observed in 3 of 23 (13%) MSI-H, in 28 of 44 (64%) MSI-L, and in 6 of 23 (26%) MSS colorectal carcinomas (P < 0.0001; Fig. 1 ). K-ras was mutated in 1 of 23 MSI-H, in 21 of 44 MSI-L, and in 7 of 23 MSS cancers (P = 0.003). Within the MSI-L subset, K-ras mutation correlated with MGMT methylation (P < 0.0002; Table 1 ). Manual sequencing identified nucleotide substitutions in 24 of 29 cancer samples with a K-ras mutation: G to A in 14 (58%); G to T in 8 (33%); and G to C in 2 (8%). The frequency of mutational bandshifts in MYCL and D2S123 (the most commonly mutated microsatellite loci in MSI-L cancers) is shown for MSI-L cancers stratified by MGMT methylation and K-ras mutation status (Table 1) . Bandshifts in MYCL were present in 28 of 42 informative MSI-L cancers (67%), and showed no correlation with MGMT methylation or K-ras mutational status (Table 1) . By contrast, bandshifts in D2S123 occurred in 10 of 42 informative MSI-L (24%) cancers but were significantly correlated with MGMT methylation (P < 0.05) and positively associated with K-ras mutation, although this fell short of statistical significance (P = 0.07). K-ras was mutated in 3 of 6 (50%) MSS cancers with MGMT methylation and in 4 of 16 (25%) unmethylated MSS cancers, the trend falling short of significance (P = 0.33).

View larger version (24K): [in this window] [in a new window] [Download PPT slide]   Fig. 1. Methylation-specific PCR. A, normal (N) and tumor (T) samples amplified with primers specific for unmethylated (bisulfite-modified) DNA, indicating the presence of unmethylated DNA in all samples. B, N and T samples from the same patients amplified with methylation-specific primers, indicating the presence of methylated DNA only in the tumor of patient 2.

View larger version (99K): [in this window] [in a new window] [Download PPT slide]   Fig. 2. Immunohistochemical staining for MGMT showing retained nuclear staining (A) and loss of nuclear staining (B) and with absent and present MGMT methylation, respectively, in colorectal cancers. Note positive internal control provided by stromal cells in B (x250; ABC technique). C, dysplastic subclone with budding crypts in a MSS hyperplastic polyp showing loss of expression of MGMT (x125; ABC technique).

	Discussion

Top ABSTRACT Introduction Materials and Methods Results Discussion REFERENCES

We have shown that MGMT methylation is strongly associated with sporadic MSI-L cancers, though is not restricted to this subset. Additionally, K-ras mutation and MGMT are highly correlated within MSI-L cancers. These observations are consistent with the suggestion that methylation and subsequent inactivation of MGMT overloads the mismatch repair system resulting in a mild mutator phenotype and, in turn, predisposing to mutation in K-ras. We could not confirm a selective association between G to A transition in K-ras and MGMT methylation (18) .

The high frequency of MYCL mutation can only be partially explained by the loss of MGMT function in view of the high rate of MYCL mutation in cancers with unmethylated MGMT (Table 1) . An alternate mechanism may explain MYCL mutation in cancers with functioning MGMT. MSS cancers showing MGMT methylation could be underdiagnosed MSI-L cancers, because the microsatellite markers used in this study are not 100% sensitive for MSI-L status. K-ras is mutated more frequently in MSS cancers with MGMT methylation, although the trend falls short of significance. The combination of MGMT silencing and loss of DNA mismatch repair proficiency in MSI-H cancers might lead to a mutational burden that would be unsustainable and would therefore trigger apoptosis. This would explain the infrequent finding of both MGMT methylation and K-ras mutation in MSI-H colorectal cancer (11) . Nevertheless, MGMT methylation was demonstrated in 3 of 23 MSI-H cancers and immunohistochemical loss occurred in 2 of 5 MSI-H serrated polyps, indicating that mutual exclusivity of MGMT silencing and MSI-H is not absolute.

K-ras mutation appears to initiate the development of crypt hyperplasia and serration that characterizes common types of ACF that are believed to be the forerunners of hyperplastic polyps and some adenomas (12) . Paradoxically, the frequency of K-ras mutation is higher within ACF than in hyperplastic polyps (9) . It is possible that ACF with potential for progression may show MGMT methylation (and may subsequently develop mutations including K-ras), whereas ACF that do not progress are initiated by K-ras mutation in isolation. Immunohistochemical staining patterns for MGMT in hyperplastic polyps, mixed polyps, and serrated adenomas indicate that only a subset of these lesions is likely to be initiated by MGMT methylation. Despite the fact that most MSI-L polyps included dysplastic areas, only 5 of 20 MSI-L polyps (25%) showed a loss of expression of MGMT. Moreover, in seven of the nine polyps showing a loss of MGMT staining, the loss was limited to small subclones. It is possible, however, that MGMT methylation is a fluctuating phenomenon within early lesions, with demethylation occurring after the establishment of mutated clones. Such a "hit and run" mechanism would account for mutations (including MSI) occurring in the absence of MGMT silencing.

MSI-L status in colorectal cancer appears to have both biological and clinical significance. We have shown previously that distant metastases at the time of diagnosis of MSI-H, MSI-L, and MSS colorectal cancers were present in 4, 21, and 14% of cases, respectively, although the trend fell short of significance (23) . It is nevertheless interesting that mutation in K-ras is associated with methylation of MGMT (18) and with a poor prognosis (26) . These observations are now beginning to demarcate a distinct molecular pathway of colorectal tumorigenesis that differs from the classic adenoma-carcinoma sequence.

	FOOTNOTES

 
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by National Cancer Institute Grant 1-U01-CA74778 (Cooperative Family Registry for Colorectal Cancer Family Studies), the National Health and Medical Research Council of Australia, and the Walter Paulsen Memorial Tumour Bank. Vicki Whitehall was supported by the Gastroenterology Society of Australia Biomedical Research Scholarship and the Paul Mackay Bolton Research Scholarship.

² To whom requests for reprints should be addressed, at Conjoint Gastroenterology Laboratory, Bancroft Centre, Herston Road, Queensland 4029, Australia. Phone: 617-3362-0491; Fax: 617-3362-0108; E-mail: vickiWh{at}qimr.edu.au

³ The abbreviations used are: MSI, microsatellite instability; MSS, microsatellite-stable; MSI-H, MSI-high; MSI-L, MSI-low; ACF, aberrant crypt foci; MGMT, O⁶-methylguanine DNA methyltransferase; TBS, Tris-buffered saline.

Received 10/20/00. Accepted 12/11/00.

	REFERENCES

Top ABSTRACT Introduction Materials and Methods Results Discussion REFERENCES

 

1. Kinzler K. W., Vogelstein B. Lessons from hereditary colorectal cancer.. Cell, 87: 159-170, 1996.[Medline]
2. Dietmaier W., Wallinger S., Bocker T., Kullmann F., Fishel R., Rüschoff J. Diagnostic microsatellite instability: definition and correlation with mismatch repair protein expression.. Cancer Res., 57: 4749-4756, 1997.[Abstract/Free Full Text]
3. Thibodeau S. N., French A. J., Cunningham J. M., Tester D., Burgart L. J., Roche P. C., McDonnell S. K., Schaid D. J., Vockley C. W., Michels V. V., Farr G. H. J., O’Connell M. J. Microsatellite instability in colorectal cancer: different mutator phenotypes and the principle involvement of hMLH1.. Cancer Res., 58: 1713-1718, 1998.[Abstract/Free Full Text]
4. Boland C. R., Thibodeau S. N., Hamilton S. R., Sidransky D., Eshleman J. R., Burt R. W., Meltzer S. J., Rodriguez-Bigas M. A., Fodde R., Ranzani G. N., Srivastava S. A National Cancer Institute Workshop on microsatellite instability for cancer detection and familial predisposition: development of international criteria for the determination of microsatellite instability in colorectal cancer.. Cancer Res., 58: 5248-5257, 1998.[Abstract/Free Full Text]
5. Papadopoulos N., Nicolaides N. C., Liu B., Parsons R., Lengauer C., Palombo F., D’Arrigo A., Markowitz S., Willson J. K. V., Kinzler K. W., Jiricny J., Vogelstein B. Mutations of GTBP in genetically unstable cells.. Science (Washington DC), 368: 1915-1917, 1995.
6. Akiyama Y., Sato H., Yamada T., Nagasaki H., Tsuchiya A., Abe R., Yuasa Y. Germ-line mutation of the hMSH6/GTBP gene in an atypical hereditary nonpolyposis colorectal cancer kindred.. Cancer Res., 57: 3920-3923, 1997.[Abstract/Free Full Text]
7. Iino H., Jass J. R., Simms L. A., Young J., Leggett B., Ajioka Y., Watanabe H. DNA microsatellite instability in hyperplastic polyps, serrated adenomas, and mixed polyps: a mild mutator pathway for colorectal cancer?. J. Clin. Pathol., 52: 5-9, 1999.[Abstract]
8. Jass J. R., Iino H., Ruszkiewicz A., Painter D., Solomon M. J., Koorey D. J., Cohn D., Furlong K. L., Walsh M. D., Palazzo J. , Bocker Edmonston, T., Fishel, R., Young, J., and Leggett, B.. A. Neoplastic progression occurs through mutator pathways in hyperplastic polyposis of the colorectum. Gut, 47: 43-49, 2000.[Abstract/Free Full Text]
9. Rashid A., Houlihan S., Booker S., Petersen G. M., Giardiello F. M., Hamilton S. R. Phenotypic and molecular characteristics of hyperplastic polyposis.. Gastroenterology, 119: 323-332, 2000.[Medline]
10. Iino H., Simms L. A., Young J., Arnold J., Winship I. M., Webb S. I., Furlong K. L., Leggett B., Jass J. R. DNA microsatellite instability and mismatch repair protein loss in adenomas presenting in hereditary non-polyposis colorectal cancer.. Gut, 47: 37-42, 2000.[Abstract/Free Full Text]
11. Jass J. R., Biden K. G., Cummings M., Simms L. A., Walsh M., Schoch E., Meltzer S., Wright C., Searle J., Young J., Leggett B. A. Characterisation of a subtype of colorectal cancer combining features of the suppressor and mild mutator pathways.. J. Clin. Pathol., 52: 455-460, 1999.[Abstract]
12. Jen J., Powell S. M., Papadopoulos N., Smith K. J., Hamilton S. R., Vogelstein B., Kinzler K. W. Molecular determinants of dysplasia in colorectal lesions.. Cancer Res., 54: 5523-5526, 1994.[Abstract/Free Full Text]
13. Nascimbeni R., Villanacci V., Mariani P. P., Di Betta E., Ghirardi M., Donato F., Salerni B. Aberrant crypt foci in the human colon.. Am. J. Surg. Pathol., 23: 1256-1263, 1999.[Medline]
14. Heinen C. D., Shivapurkar N., Tang Z., Groden J., Alabaster O. Microsatellite instability in aberrant crypt foci from human colons.. Cancer Res., 56: 5339-5341, 1996.[Abstract/Free Full Text]
15. Sakurazawa N., Tanaka N., Onda M., Esumi H. Instability of X chromosome methylation in aberrant crypt foci of the human colon.. Cancer Res., 60: 3165-3169, 2000.[Abstract/Free Full Text]
16. Pegg A. E., Dolan M. E., Moschel R. C. Structure, function and inhibition of 0⁶-alkylguanine-DNA alkyltransferase.. Prog. Nucleic Acid Res. Mol. Biol., 51: 167-223, 1995.[Medline]
17. Mitra G., Pauly G. T., Kumar R., Pei G. K., Hughes S. H., Moschel R. C., Barbacid M. Molecular analysis of O⁶-substituted guanine-induced mutagenesis of ras oncogenes. Proc. Natl. Acad. Sci. USA, 86: 8650-8654, 1989.[Abstract/Free Full Text]
18. Esteller M., Toyota M., Sanchez-Cespedes M., Capella G., Peinado M. A., Watkins D. N., Issa J-P. J., Sidransky D., Baylin S. B., Herman J. G. Inactivation of the DNA repair gene O⁶-Methylguanine-DNA Methyltransferase by promoter hypermethylation is associated with G to A mutations in K-ras in colorectal tumorigenesis. Cancer Res., 60: 2368-2371, 2000.[Abstract/Free Full Text]
19. Herman J. G., Graff J. R., Myohanen S., Nelkin B. D., Baylin S. B. Methylation-specific PCR.. A novel PCR assay for methylation status of CpG islands. Proc. Natl. Acad. Sci. USA, 93: 9821-9826, 1996.[Abstract/Free Full Text]
20. Jiang W., Kahn S., Guillem J., Lu S., Weinstein I. Rapid detection of ras oncogenes in human tumors: applications to colon, eosophageal, and gastric cancer.. Oncogene, 4: 923-928, 1989.[Medline]
21. Kim H., Jen J., Vogelstein B., Hamilton S. R. Clinical and pathological characteristics of sporadic colorectal carcinomas with DNA replication errors in microsatellite sequences.. Am. J. Pathol., 145: 148-156, 1994.[Abstract]
22. Rüschoff J., Dietmaier W., Lüttges J., Seitz G., Bocker T., Zirngibl H., Schlegel J., Schackert H. K., Jauch K. W., Hofstaedter F. Poorly differentiated colonic adenocarcinoma, medullary type: clinical, phenotypic, and molecular characteristics.. Am. J. Pathol., 150: 1815-1825, 1997.[Abstract]
23. Jass J. R., Do K-A., Simms L. A., Iino H., Wynter C., Pillay S. P., Searle J., Radford-Smith G., Young J., Leggett B. Morphology of sporadic colorectal cancer with DNA replication errors.. Gut, 42: 673-679, 1998.[Abstract/Free Full Text]
24. Biden K. G., Simms L. A., Cummings M., Buttenshaw R., Schoch E., Searle J., Gobé G., Jass J. R., Meltzer S. J., Leggett B. A., Young J. Expression of Bcl-2 protein is decreased in colorectal adenocarcinomas with microsatellite instability.. Oncogene, 17: 1245-1249, 1999.
25. Michael-Robinson, J. M., Biemer-Hüttman, A.-E., Purdie, D. M., Walsh, M. D., Simms, L. A., Biden, K. G., Young, J. P., Leggett, B. A., Jass, J. R., and Radford-Smith, G. L. Tumour infiltrating lymphocytes and apoptosis are independent features in colorectal cancer stratified according to microsatellite instability status. Gut, in press, 2001.
26. Span M., Moerkerk P. T. M., De Goeij A. F. P. M., Arends J. W. A detailed analysis of K-ras point mutations in relation to tumor progression and survival in colorectal cancer patients.. Int. J. Cancer, 69: 241-245, 1996.[Medline]

This article has been cited by other articles:

				H. A. Billson, K. L. Harrison, N. P. Lees, C. N. Hall, G. P. Margison, and A. C. Povey Dietary variables associated with DNA N7-methylguanine levels and O6-alkylguanine DNA-alkyltransferase activity in human colorectal mucosa Carcinogenesis, April 1, 2009; 30(4): 615 - 620. [Abstract] [Full Text] [PDF]

				K. Imai and H. Yamamoto Carcinogenesis and microsatellite instability: the interrelationship between genetics and epigenetics Carcinogenesis, April 1, 2008; 29(4): 673 - 680. [Abstract] [Full Text] [PDF]

				V. Deschoolmeester, M. Baay, W. Wuyts, E. Van Marck, N. Van Damme, P. Vermeulen, K. Lukaszuk, F. Lardon, and J. B. Vermorken Detection of Microsatellite Instability in Colorectal Cancer Using an Alternative Multiplex Assay of Quasi-Monomorphic Mononucleotide Markers J. Mol. Diagn., March 1, 2008; 10(2): 154 - 159. [Abstract] [Full Text] [PDF]

				S. Ogino and A. Goel Molecular Classification and Correlates in Colorectal Cancer J. Mol. Diagn., January 1, 2008; 10(1): 13 - 27. [Abstract] [Full Text] [PDF]

				W. M Grady CIMP and colon cancer gets more complicated Gut, November 1, 2007; 56(11): 1498 - 1500. [Full Text] [PDF]

				S. Ogino, T. Kawasaki, G. J Kirkner, Y. Suemoto, J. A Meyerhardt, and C. S Fuchs Molecular correlates with MGMT promoter methylation and silencing support CpG island methylator phenotype-low (CIMP-low) in colorectal cancer Gut, November 1, 2007; 56(11): 1564 - 1571. [Abstract] [Full Text] [PDF]

				S. Ogino, A. Hazra, G. J. Tranah, G. J. Kirkner, T. Kawasaki, K. Nosho, M. Ohnishi, Y. Suemoto, J. A. Meyerhardt, D. J. Hunter, et al. MGMT germline polymorphism is associated with somatic MGMT promoter methylation and gene silencing in colorectal cancer Carcinogenesis, September 1, 2007; 28(9): 1985 - 1990. [Abstract] [Full Text] [PDF]

				F. V. Jacinto and M. Esteller Mutator pathways unleashed by epigenetic silencing in human cancer Mutagenesis, July 1, 2007; 22(4): 247 - 253. [Abstract] [Full Text] [PDF]

				E. J. Greenspan, J. L. Cyr, D. C. Pleau, J. Levine, T. V. Rajan, D. W. Rosenberg, and C. D. Heinen Microsatellite instability in aberrant crypt foci from patients without concurrent colon cancer Carcinogenesis, April 1, 2007; 28(4): 769 - 776. [Abstract] [Full Text] [PDF]

				N P Lees, K L Harrison, C N Hall, G P Margison, and A C Povey Human colorectal mucosal O6-alkylguanine DNA-alkyltransferase activity and DNA-N7-methylguanine levels in colorectal adenoma cases and matched referents Gut, March 1, 2007; 56(3): 380 - 384. [Abstract] [Full Text] [PDF]

				K. M. Murphy, S. Zhang, T. Geiger, M. J. Hafez, J. Bacher, K. D. Berg, and J. R. Eshleman Comparison of the Microsatellite Instability Analysis System and the Bethesda Panel for the Determination of Microsatellite Instability in Colorectal Cancers J. Mol. Diagn., July 1, 2006; 8(3): 305 - 311. [Abstract] [Full Text] [PDF]

				G. Lanza, R. Gafa, A. Santini, I. Maestri, L. Guerzoni, and L. Cavazzini Immunohistochemical Test for MLH1 and MSH2 Expression Predicts Clinical Outcome in Stage II and III Colorectal Cancer Patients J. Clin. Oncol., May 20, 2006; 24(15): 2359 - 2367. [Abstract] [Full Text] [PDF]

				T. Sugai, W. Habano, Y.-F. Jiao, M. Tsukahara, Y. Takeda, K. Otsuka, and S.-i. Nakamura Analysis of Molecular Alterations in Left- and Right-Sided Colorectal Carcinomas Reveals Distinct Pathways of Carcinogenesis: Proposal for New Molecular Profile of Colorectal Carcinomas J. Mol. Diagn., May 1, 2006; 8(2): 193 - 201. [Abstract] [Full Text] [PDF]

				E. J. Fox, D. T. Leahy, R. Geraghty, H. E. Mulcahy, D. Fennelly, J. M. Hyland, D. P. O'Donoghue, and K. Sheahan Mutually Exclusive Promoter Hypermethylation Patterns of hMLH1 and O6-Methylguanine DNA Methyltransferase in Colorectal Cancer J. Mol. Diagn., February 1, 2006; 8(1): 68 - 75. [Abstract] [Full Text] [PDF]

				L. Shen, Y. Kondo, G. L. Rosner, L. Xiao, N. S. Hernandez, J. Vilaythong, P. S. Houlihan, R. S. Krouse, A. R. Prasad, J. G. Einspahr, et al. MGMT Promoter Methylation and Field Defect in Sporadic Colorectal Cancer J Natl Cancer Inst, September 21, 2005; 97(18): 1330 - 1338. [Abstract] [Full Text] [PDF]

				S Halford, A Rowan, E Sawyer, I Talbot, and I Tomlinson O6-methylguanine methyltransferase in colorectal cancers: detection of mutations, loss of expression, and weak association with G:C>A:T transitions Gut, June 1, 2005; 54(6): 797 - 802. [Abstract] [Full Text] [PDF]

				M. R.J. Kohonen-Corish, J. J. Daniel, C. Chan, B. P.C. Lin, S. Y. Kwun, O. F. Dent, V. S. Dhillon, R. J.A. Trent, P. H. Chapuis, and E. L. Bokey Low Microsatellite Instability Is Associated With Poor Prognosis in Stage C Colon Cancer J. Clin. Oncol., April 1, 2005; 23(10): 2318 - 2324. [Abstract] [Full Text] [PDF]

				T. Fukushima, Y. Katayama, T. Watanabe, A. Yoshino, A. Ogino, T. Ohta, and C. Komine Promoter Hypermethylation of Mismatch Repair Gene hMLH1 Predicts the Clinical Response of Malignant Astrocytomas to Nitrosourea Clin. Cancer Res., February 15, 2005; 11(4): 1539 - 1544. [Abstract] [Full Text] [PDF]

				C M Wright, O F Dent, R C Newland, M Barker, P H Chapuis, E L Bokey, J P Young, B A Leggett, J R Jass, and G A Macdonald Low level microsatellite instability may be associated with reduced cancer specific survival in sporadic stage C colorectal carcinoma Gut, January 1, 2005; 54(1): 103 - 108. [Abstract] [Full Text] [PDF]

				T. Nagasaka, H. Sasamoto, K. Notohara, H. M. Cullings, M. Takeda, K. Kimura, T. Kambara, D. G. MacPhee, J. Young, B. A. Leggett, et al. Colorectal Cancer With Mutation in BRAF, KRAS, and Wild-Type With Respect to Both Oncogenes Showing Different Patterns of DNA Methylation J. Clin. Oncol., November 15, 2004; 22(22): 4584 - 4594. [Abstract] [Full Text] [PDF]

				N. P. Lees, K. L. Harrison, C. N. Hall, G. P. Margison, and A. C. Povey Reduced MGMT activity in human colorectal adenomas is associated with K-ras GC->AT transition mutations in a population exposed to methylating agents Carcinogenesis, July 1, 2004; 25(7): 1243 - 1247. [Abstract] [Full Text] [PDF]

				C V A Wynter, M D Walsh, T Higuchi, B A Leggett, J Young, and J R Jass Methylation patterns define two types of hyperplastic polyp associated with colorectal cancer Gut, April 1, 2004; 53(4): 573 - 580. [Abstract] [Full Text] [PDF]

				T. Nagasaka, G. B. Sharp, K. Notohara, T. Kambara, H. Sasamoto, H. Isozaki, D. G. MacPhee, J. R. Jass, N. Tanaka, and N. Matsubara Hypermethylation of O6-Methylguanine-DNA Methyltransferase Promoter May Predict Nonrecurrence after Chemotherapy in Colorectal Cancer Cases Clin. Cancer Res., November 1, 2003; 9(14): 5306 - 5312. [Abstract] [Full Text] [PDF]

				G.M. Nash, M. Gimbel, J. Shia, A.T. Culliford, D.R. Nathanson, M. Ndubuisi, Y. Yamaguchi, Z.S. Zeng, F. Barany, and P.B. Paty Automated, Multiplex Assay for High-Frequency Microsatellite Instability in Colorectal Cancer J. Clin. Oncol., August 15, 2003; 21(16): 3105 - 3112. [Abstract] [Full Text] [PDF]

				Y. Mori, F. M. Selaru, F. Sato, J. Yin, L. A. Simms, Y. Xu, A. Olaru, E. Deacu, S. Wang, J. M. Taylor, et al. The Impact of Microsatellite Instability on the Molecular Phenotype of Colorectal Tumors Cancer Res., August 1, 2003; 63(15): 4577 - 4582. [Abstract] [Full Text] [PDF]

				L. Zhang, W. Lu, X. Miao, D. Xing, W. Tan, and D. Lin Inactivation of DNA repair gene O6-methylguanine-DNA methyltransferase by promoter hypermethylation and its relation to p53 mutations in esophageal squamous cell carcinoma Carcinogenesis, June 1, 2003; 24(6): 1039 - 1044. [Abstract] [Full Text] [PDF]

				P. Peltomaki Role of DNA Mismatch Repair Defects in the Pathogenesis of Human Cancer J. Clin. Oncol., March 15, 2003; 21(6): 1174 - 1179. [Abstract] [Full Text] [PDF]

				A Davenport, R J Hale, C R Hunt, G Bigley, and R F T McMahon Expression of Ki-67 and cytokeratin 20 in hyperplastic polyps of the colorectum J. Clin. Pathol., March 1, 2003; 56(3): 200 - 204. [Abstract] [Full Text] [PDF]

				J. R. Jass Serrated Adenoma of the Colorectum: A Lesion with Teeth Am. J. Pathol., March 1, 2003; 162(3): 705 - 708. [Full Text] [PDF]

				J R Jass, M Barker, L Fraser, M D Walsh, V L J Whitehall, B Gabrielli, J Young, and B A Leggett APC mutation and tumour budding in colorectal cancer J. Clin. Pathol., January 1, 2003; 56(1): 69 - 73. [Abstract] [Full Text] [PDF]

				N J Maughan and P Quirke Pathology - a molecular prognostic approach: Advances in colorectal cancer Br. Med. Bull., December 1, 2002; 64(1): 59 - 74. [Abstract] [Full Text] [PDF]

				V. L. J. Whitehall, C. V. A. Wynter, M. D. Walsh, L. A. Simms, D. Purdie, N. Pandeya, J. Young, S. J. Meltzer, B. A. Leggett, and J. R. Jass Morphological and Molecular Heterogeneity within Nonmicrosatellite Instability-High Colorectal Cancer Cancer Res., November 1, 2002; 62(21): 6011 - 6014. [Abstract] [Full Text] [PDF]

				A. C. Povey, A. F. Badawi, D. P. Cooper, C. N. Hall, K. L. Harrison, P. E. Jackson, N. P. Lees, P. J. O'Connor, and G. P. Margison DNA Alkylation and Repair in the Large Bowel: Animal and Human Studies J. Nutr., November 1, 2002; 132(11): 3518S - 3521. [Abstract] [Full Text] [PDF]

				J. R. Jass, V. L. J. Whitehall, J. Young, B. Leggett, S. J. Meltzer, N. Matsubara, R. Fishel, P. Laiho, and L. A. Aaltonen Correspondence re: P. Laiho et al., Low-Level Microsatellite Instability in Most Colorectal Carcinomas. Cancer Res., 62: 1166-1170, 2002. Cancer Res., October 15, 2002; 62(20): 5988 - 5990. [Full Text] [PDF]

				E J Sawyer, A Cerar, A M Hanby, P Gorman, M Arends, I C Talbot, and I P M Tomlinson Molecular characteristics of serrated adenomas of the colorectum Gut, August 1, 2002; 51(2): 200 - 206. [Abstract] [Full Text] [PDF]

				S. Richman and J. Adlard Left and right sided large bowel cancer BMJ, April 20, 2002; 324(7343): 931 - 932. [Full Text] [PDF]

				A. Muller, T. B. Edmonston, D. A. Corao, D. G. Rose, J. P. Palazzo, H. Becker, R. D. Fry, J. Rueschoff, and R. Fishel Exclusion of Breast Cancer as an Integral Tumor of Hereditary Nonpolyposis Colorectal Cancer Cancer Res., February 1, 2002; 62(4): 1014 - 1019. [Abstract] [Full Text] [PDF]

				P. Laiho, V. Launonen, P. Lahermo, M. Esteller, M. Guo, J. G. Herman, J.-P. Mecklin, H. Jarvinen, P. Sistonen, K.-M. Kim, et al. Low-Level Microsatellite Instability in Most Colorectal Carcinomas Cancer Res., February 1, 2002; 62(4): 1166 - 1170. [Abstract] [Full Text] [PDF]

				A. O.-O. Chan, J.-P. J. Issa, J. S. Morris, S. R. Hamilton, and A. Rashid Concordant CpG Island Methylation in Hyperplastic Polyposis Am. J. Pathol., February 1, 2002; 160(2): 529 - 536. [Abstract] [Full Text] [PDF]

				S. Halford, P. Sasieni, A. Rowan, H. Wasan, W. Bodmer, I. Talbot, N. Hawkins, R. Ward, and I. Tomlinson Low-Level Microsatellite Instability Occurs in Most Colorectal Cancers and Is a Nonrandomly Distributed Quantitative Trait Cancer Res., January 1, 2002; 62(1): 53 - 57. [Abstract] [Full Text] [PDF]

				J. Young, L. A. Simms, K. G. Biden, C. Wynter, V. Whitehall, R. Karamatic, J. George, J. Goldblatt, I. Walpole, S.-A. Robin, et al. Features of Colorectal Cancers with High-Level Microsatellite Instability Occurring in Familial and Sporadic Settings : Parallel Pathways of Tumorigenesis Am. J. Pathol., December 1, 2001; 159(6): 2107 - 2116. [Abstract] [Full Text] [PDF]

				T. Kambara, N. Matsubara, H. Nakagawa, K. Notohara, T. Nagasaka, T. Yoshino, H. Isozaki, G. B. Sharp, K. Shimizu, J. Jass, et al. High Frequency of Low-Level Microsatellite Instability in Early Colorectal Cancer Cancer Res., November 1, 2001; 61(21): 7743 - 7746. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Whitehall, V. L. J. Articles by Jass, J. R. Search for Related Content PubMed PubMed Citation Articles by Whitehall, V. L. J. Articles by Jass, J. R.