Microsatellite Instability in Sporadic Colorectal Cancer: A Retrospective Study
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Transcript of Microsatellite Instability in Sporadic Colorectal Cancer: A Retrospective Study
Microsatellite Instability in Sporadic Colorectal Cancer: A Retrospective Study
Kimberley SlowtherTrainee Project
West Midlands Regional Genetics Laboratory
Colorectal Cancer 35,000 diagnosed per year Treatment and prognosis depend upon
tumour stage
Causes of CRC
Sporadic 75%
Rare Syndromes
<1%
FAP 1%
HNPCC 5%
Familial 19%
Genetic Pathways in CRC Microsatellite Instability (MSI-H)
Deficiency in DNA mismatch repair (MMR) HNPCC (MSH2, MLH1, MSH6, PMS2) 15% sporadic (hypermethylation of MLH1
promoter)
Chromosomal Instability (CIN) APC, TP53, KRAS, Loss of Heterozygosity,
aneuploid DNA content
CpG Island Methylator Phenotype (CIMP) Methylation of CpG islands in promoter
regions of tumour suppressor genes Sporadic CRCs demonstrating MSI are a subset
Microsatellite Instability
Normal
Tumour
Normal
Tumour
Comparison of Sporadic MSI-H with HNPCC Tumours
Both are MSI-H and proximally located
BUT Sporadic MSI-H:- Greater predilection for the proximal colon Higher frequency of BRAF mutations Lower frequency of KRAS mutations More age related More common in females Originate from serrated polyps
HNPCC tumours originate from adenomas
RAS-RAF-MEK-ERK Pathway
BRAFSerine-threonine specific kinase40% sporadic MSI-H tumoursNot present in HNPCC Common mutation (90%) is V600E
KRASGTPase90% mutations in codons 12 and 1330-40% sporadic MSS CRC40% HNPCC
Regulates growth, differentiation and apoptosis
MSI and Prognosis MSI in CRC is a positive prognostic
indicator Better five-year rate of overall
survival than MSS tumours Less likely to metastasise Why?
Enhanced mutation rate induces a burden not compatible with tumour cell survival
Abnormal peptides produced elicit antitumour immune responses that limit tumour growth
Treatment of CRC
Dictated by stage Stage I: surgery alone Stage II, III+IV: adjuvant therapy Less clear cut with Stage II
Patients reviewed on individual basis Chemotherapy Drugs
5-fluorouracil/folinic acid (5FU/FA) to Stage II and III patients
5FU/FA and Oxaliplatin to Stage IV and fitter Stage II and III patients
MSI and Chemotherapy Resistance of MSI-H CRC to 5FU is well documented
MSS patients have increased survival with 5FU MSI-H patients do not have improved survival
following treatment Why have 5FU treatment if there is no benefit?
Oxaliplatin therapy not affected by loss of MMR Information about MSI status could impact
treatment:- Decision of whether or not to opt for adjuvant therapy Allocation patients to oxaliplatin therapy
Project Aim
Investigate whether microsatelliteanalysis of sporadic colorectal
cancer would be a valuable service to offer
in future in order to tailor patient treatment
Methods MSI status of patients with locally advanced, treatable
sporadic (absence of family history) CRC 41 – Department of Surgery Epithelial Research Group 32 – Department of Histopathology
7 microsatellite markers MSI-H if instability present at 2 or more markers MSI-L if instability present at 1 marker
Analysed MSI data in relation to:- Age at diagnosis Gender BRAF exon 15 mutation KRAS codon 12 and 13 mutation (41/73) Tumour site Tumour differentiation
Results: Microsatellite Status and Age
On average patients demonstrating MSI in their tumours were younger but this was not statistically significant
Of the 14 patient samples demonstrating MSI, 7 were older than 70 at diagnosis
Usually opt not to be treated with adjuvant therapy; MSI status could be used to help make this decision
Plus-minus values are means ±SD.
Total
MSI-H
MSS + MSI-L
P valu
e
Mean age (y ± SD)
69±14
66±17
70±13 0.36
Results: Microsatellite Status and Gender
More female samples demonstrated MSI-H but this was not statistically significant
TotalMSI-
HMSS + MSI-
LP
value
Gender (%)
Male 36
(49)5 (7) 31 (43)
0.26Female
37 (51)
9 (12) 28 (38)
Results: Microsatellite Status and Tumour Differentiation
MSI-H tumours more poorly differentiated than MSS or MSI-L tumours
TotalMSI-
HMSS + MSI-
L
Differentiation (%)
Poor 10 (15) 6 (9) 4 (6)
Moderate
49 (71) 7 (10) 42 (61)
Well 10 (15) 0 (0) 10 (15)
Results: Microsatellite Status and Tumour Site
MSI-H associated with localisation of tumour to the proximal colon
TotalMSI-
HMSS + MSI-
LP
value
Cancer Site (%)
Proximal
34 (44)
11 (14)
23 (30)0.011
Distal 43 (56)
4 (5) 39 (51)
Results: Microsatellite Status and BRAF/KRAS Mutations
KRAS mutations and BRAF mutations were mutually exclusive
MSS and MSI-L tumours had a higher frequency of KRAS mutations
MSI-H tumours higher frequency of BRAF mutations
Total
MSI-H
MSS + MSI-L
KRAS mutation (%)
11 1 (9) 10 (91)
BRAF mutation (%)
22
(100)0
Discussion What are the benefits of MSI analysis for
sporadic CRC? Improved patient care
MSI-H not given unnecessary treatment (5-FU) MSI-H allocated to more effective treatments
(Oxaliplatin) ? Cost Benefit
Reduced chemotherapy?
Perhaps not all tumours were sporadic Ethical Implications
Possibility that HNPCC patients included Only 14% MSI-H samples contained BRAF mutations
Recommend that patients are counselled
Future Developments
Prospective study Treatment vs no treatment
? Unethical Complicated by wide use of oxaliplatin
Oxaliplatin vs 5FU In the future just offer oxaliplatin therapy
to MSI-H patients
Conclusion
Techniques available to put a system into place to offer MSI analysis of sporadic colorectal tumours
Tailor patient treatment depending upon tumour stage, microsatellite status and age
Acknowledgements West Midlands Regional Genetics Laboratory
Fiona Macdonald Jennie Bell Kerry Wall
University of Birmingham Department of Surgery Epithelial Research Group
Dion Morton Germaine Caldwell
University Hospital of Birmingham Histopathology Department
Philippe Taniere Brendan O’Sullivan Graham Caine