Biomarkers in Cancer

771 Pages·2015·18.578 MB·English

by  Victor R. Preedy, Vinood B. Patel (eds.)

BiomarkersinCancer
DOI10.1007/978-94-007-7744-6_1-1
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Biomarkers in Metastatic Colorectal Cancer
PredictingPrognosisandTherapeuticResponse
ConnieI.Diakosa,KellieA.Charlesb,WeiChuac,ViiveM.HowellaandStephenJ.Clarkea*
aKollingInstituteofMedicalResearch,RoyalNorthShoreHospital,UniversityofSydney,StLeonards,NSW,Australia
bSchoolofMedicalSciences(Pharmacology),SydneyMedicalSchool,UniversityofSydney,StLeonards,NSW,Australia
cDepartmentofMedicalOncology,LiverpoolHospital,Liverpool,NSW,Australia
Abstract
Significant advances in chemotherapeutics over the past decade have seen a doubling in the median
survival time of patients with metastatic colorectal cancer. However, this comes at the cost of toxicity to
the patient and financial burden to the community. Biomarkers to predict disease course and treatment
response are therefore of major importance so as to allow for the judicious selection of treatment
candidates and agents and doses. This review seeks to summarize the current markers available for the
prediction of prognosis and treatment response in metastatic colorectal cancer.
List of Abbreviations
5-FU 5-fluorouracil
ASCO American Society of Clinical Oncology
BMI Body Mass Index
BSA Body Surface Area
CRP C-Reactive Protein
DACH Diaminocyclohexane
DFS Disease-Free Survival
DNA Deoxyribonucleic Acid
DPD Dihydropyrimidine Dehydrogenase
EGFR Epithelial Growth Factor Receptor
ERCC-1 Excision Repair Cross-Complementing Group 1
GPS Glasgow Prognosis Score
GST Glutathione-S-Transferase
HIF-1a Hypoxia-Inducible Factor 1a
KRAS Kirsten Rat Sarcoma Viral Oncogene
LDH Lactate Dehydrogenase
mAb Monoclonal Antibody
MAPK Mitogen-Activated Protein Kinase
mCRC Metastatic Colorectal Cancer
MMR Mismatch Repair
MSI Microsatellite Instability
MSS Microsatellite Stability
MTHFR Methylenetetrahydrofolate Reductase
*Email:[email protected]
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NF-kb Nuclear Factor-kb
NLR Neutrophil to Lymphocyte Ratio
NRAS Neuroblastoma Ras
OS Overall Survival
PD-ECGF Platelet-Derived Endothelial Cell Growth Factor
PFS Progression-Free Survival
PI3K Phosphatidylinositol-3-kinase
PLR Platelet to Lymphocyte Ratio
RCT Randomized Controlled Trial
RNA Ribonucleic Acid
RR Response Rate
SNP Single-Nucleotide Polymorphism
STAT3 Signal Transducers and Activators of Transcription 3
TCGA The Cancer Genome Atlas
THBS2 Thrombospondin-2
Topo-1 Topoisomerase-1
TP Thymidine Phosphorylase
TS Thymidylate Synthase
UGT Uridine-Diphosphoglucuronosyl Transferase
VEGF Vascular Endothelial Growth Factor
WT Wild Type
XPD Xeroderma Pigmentosum Complementation Group D
XRCC-1 X-Ray Repair Cross-Complementing Protein 1
Key Facts of Biomarkers in Metastatic Colorectal Cancer
(cid:129) Colorectalcancer(CRC)isthesecondmostprevalentcancerworldwideandthethirdleadingcauseof
cancer-related death.
(cid:129) CRC is largely a disease of the elderly, with a median age of 69 years at diagnosis.
(cid:129) Whendiagnosedintheearlystages,CRCisoneofthemostcurableofcancers.However,20–25%of
patients already have metastatic disease at the time of diagnosis, i.e., cancer that has already spread
beyondthebowel,whichisgenerallyincurable.Afurther25%ofpatientswithearly-stagediseasewill
progress to metastatic disease following their surgery.
(cid:129) Advances in chemotherapy and targeted agents over the past 10 years have seen a doubling of the
median survival of patients with metastatic CRC (mCRC).
(cid:129) Thesignificantcosts,bothfinancialandintermsofsideeffects,makeappropriateselectionoftreatment
candidates vital.
(cid:129) The personalization of cancer medicine through the use of biomarkers that predict disease course or
response to therapy is a hallmark of modern medical oncology.
(cid:129) Few biomarkers exist that accurately and consistently predict prognosis or treatment response, so
continued research in this area is highly important.
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Definitions of Words and Terms
Bevacizumab A monoclonal antibody against VEGF used in the treatment of metastatic colorectal
cancer.
Biomarker Anyentitythatallowsforindividualizedpredictionofdiseasecourseorresponsetotherapy.
Cetuximab AmonoclonalantibodyagainstEGFRusedinthetreatmentofmetastaticcolorectalcancer.
Chemotherapy Chemical agents used in the systemic treatment of cancer.
Colorectal Cancer Cancer of the large bowel or rectum.
Epithelial Growth Factor Receptor (EGFR) A cell surface receptor frequently overexpressed in
epithelial tumors.
Panitumumab A monoclonal antibody against EGFR used in the treatment of metastatic colorectal
cancer.
Predictive Biomarker An entity that describes the impact of a treatment on outcome.
Prognostic Biomarker A factor relating to outcome that is independent of treatment.
TargetedAagents/TargetedAntibodies Biologicalagentsagainstspecificmoleculartargetsinatumor.
Vascular Endothelial Growth Factor (VEGFR) A cell surface receptor linked to blood vessel forma-
tion in tumors and normal tissues.
Wild Type A gene that is unmutated.
Introduction
Colorectal cancer (CRC) is one of the most common of cancers and one of the leading causes of cancer
mortalityworldwide.Yetitisalsooneofthemosttreatable.While40–50%ofpatientsdeveloporpresent
with metastatic disease, significant advances in chemotherapeutics and targeted agents over the past
decadehaveseenadoublinginthemedianoverallsurvivalofpatientswithmetastaticCRC(mCRC)from
10 to more than 20 months. However, these improvements come at a cost, of a financial nature to
government health budgets and of toxicities to the individual patient. Hence the selection of appropriate
drugs and treatment candidates is paramount, especially in this new age of personalized medicine.
Predictive and prognostic biomarkers are vital in facilitating the ongoing personalization of treatment
for mCRC. Predictive biomarkers pertain to the impact of specific treatments on outcome, described by
response rates or survival. Prognostic biomarkers relate to outcomes that are independent of treatment.
There are few biomarkers in routine clinical use currently for mCRC, including tumor-node-metastasis
stagingandhistopathologicalfeatureswiththeirwell-establishedprognosticrole.However,thesedonot
provideinformationoftreatmentresponse;todate,onlyKRASmutationstatushasattainedroutineclinical
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use in mCRC, with the negative impact of KRAS mutations on treatment with epithelial growth factor
receptor (EGFR) inhibitors now well established.
ThisreviewsummarizestheadvancesmadeintothepersonalizationofmCRCtreatmentbyexamining
theevidencearoundexistingbiomarkersanddiscussespotentialnewmarkersforthepredictionofdisease
course and treatment response.
Prognostic Biomarkers
Few prognostic markers exist for mCRC. Tumor staging and histopathological features are well
established, but the majority of other entities examined have not been consistent in their utility between
studies (summarized in Table 1).
Inflammation
Inflammationisacardinalfeatureofmalignancy,contributingtothedevelopmentofcancersandplaying
akeyroleincancerprogression(Colottaetal.2009;HanahanandWeinberg2011).Inestablishedcancers,
inflammatorysymptomssuchasfevers,sweats,andweightlossoccurcommonly,andevidenceexiststhat
a systemic inflammatory response is predictive of worse outcomes in a number of malignancies, with
earlier cancer recurrence and reduced cancer-specific survival (Clarke et al. 2011; Moore et al. 2010).
Inflammation has also been shown to result in slower clearance of anticancer drugs and worse toxicities
(Robertson et al. 2008; Kacevska et al. 2008).
Bothlocalandsystemicinflammationshavedemonstratedrolesinprognosis(RoxburghandMcMillan
2010,2012).Systemicinflammationappearstobemediatedbythereleaseofproinflammatorycytokines
from the tumor itself, its supporting vasculature, and/or stroma (Charles et al. 2006). Chronic inflamma-
tionmaybeinvolvedinthedevelopmentandprogressionofcancersthroughanumberofpathways,such
asnuclearfactor-kb(NF-kb)andsignaltransducersandactivatorsoftranscription3(STAT3)(Aggarwal
et al. 2009).
Table1 PrognosticfactorsinmCRC
Factor Evidence Utility Reference
Patientage>85 Conclusive Negativeprognosticfactor Fieldetal.2008
years
Obesity Limited Extremelyobesepatientshavehigherriskoflocalrecurrence Dignametal.2006
andcancer-specificmortality
Smoking Inconclusive Heavysmokershaveworseoutcome McClearyetal.2010
Exercise Limited Lowerriskofrecurrencewithmoreexercise Meyerhardtetal.2006
Glasgow Limited Abnormalscoreassociatedwithworseoutcomeafter McMillan2013
prognosisscore surgicalresectionandforinoperableCRC
Neutrophil/ Limited HighratiocorrelateswithworsePFSandOSinpatients Chuaetal.2011
lymphocyteratio undergoingchemotherapy
MSI Considerable Positiveprognosticfactorinadjuvantsetting;negativein Popatetal.2005;Tran
metastaticsetting etal.2011
BRAFmutations Considerable Negativeprognosticfactor VanCutsemetal.2011b;
Samowitzetal.2005
KRASmutations Insufficient Negativeprognosticfactor Andreyevetal.2001
PIK3CA Insufficient Negativeprognosticmarkerforrectalcancer Sartore-Bianchietal.2009
mutations
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Glasgow Prognosis Score (GPS)
Over the past decade, several markers of the systemic inflammatory response have been evaluated to
determine utility as prognostic or predictive markers in CRC. These include plasma C-reactive protein
(CRP),hypoalbuminemia,andtheGlasgowprognosisscore(GPS),comprisingathree-pointscorebased
on CRP and serum albumin concentrations (McMillan 2013). The prognostic value of an abnormal
baselineGPSinmCRChasbeendemonstrated,withutilityinpredictingsurvivalinpatientsundergoing
chemotherapy, as well as grade 2/3 toxicity from capecitabine chemotherapy.
Neutrophil to Lymphocyte Ratio (NLR)
Components of the full blood count have been evaluated as biomarkers, including white cell count, the
platelet to lymphocyte ratio (PLR), and the neutrophil to lymphocyte ratio (NLR). An elevated
pretreatment white cell count and NLR were independent predictors of worse survival in patients
receiving chemotherapy for advanced CRC (Chua et al. 2011). Baseline NLR has been shown to
negativelycorrelatewithprogression-freesurvival(PFS)andoverallsurvival(OS)inpatientsundergoing
chemotherapy,withnormalizationoftheNLRafteronecycleofchemotherapyreflectiveofanimprove-
ment in survival, versus poor survival if the NLR remained abnormal (Chua et al. 2011).
Patient-Related Factors
Age
CRC is largely a disease of the elderly, with a median age of 69 years at diagnosis and an increasing
incidence with age. There is, however, little evidence to support age as either a prognostic or predictive
factor in CRC. Most of the information on the treatment response of the elderly with CRC comes from
pooledanalysesintheadjuvantsetting,wheresimilarbenefitshavebeendemonstratedirrespectiveofage.
These findings suggest that age alone is not predictive of treatment response (Sargent et al. 2001;
Goldberg et al. 2006).
Importantly,untilrecently,onlyverysmallnumbersofpatientsaged(cid:1)80havebeenincludedinclinical
trials, and those that have are a select group with good performance status and few comorbidities. Very
advanced age could, however, be considered a negative prognostic factor for mCRC, as a recent
retrospective study has demonstrated a large number of deaths occurring without disease recurrence,
from competing causesofmortality (Field etal. 2008).Withthe growing interest inonco-geriatrics, two
phase III studies targeting elderly patients with mCRC have been conducted, examining combination
chemotherapy. Nonsignificant improvements in PFS were found with the addition of a second agent
althoughreduceddosingregimensorlargeproportionsofpatientsrequiringdosereductionswereafactor
(Seymour et al. 2011b; Mitry et al. 2012).
Theperceptionthatelderlypatientsexperienceincreasedtoxicitiesfromchemotherapyisanimportant
factor in decision-making by clinicians, and a number of scoring systems to assist in the prediction of
toxicity risk have been developed (Aparicio et al. 2013; Extermann et al. 2012). The impact of age on
toxicity has been examined, with conflicting results. In general, elderly patients experience increased
severe toxicities with 5-fluorouracil (5-FU) (Sargent et al. 2001), but in combination regimens, severe
toxicities occur at similar rates to younger patients, while lower-grade toxicities are more common
(Goldberg et al. 2006; Mitry et al. 2012).
Obesity
While there is overwhelming evidence to support the association between obesity and the risk of
developing CRC, there is conflicting evidence on the prognostic value of obesity in CRC. Very obese
patients(bodymassindex[BMI](cid:1)35kg/m2)havedemonstratedhigherriskofcancerrecurrenceordeath
compared to those of normal weight, with no difference in risk of chemotherapy-related toxicities
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(Dignam et al. 2006). However, the reverse has also been found, with neither BMI nor weight change
found to be associated with increased risk of cancer recurrence or death (Meyerhardt et al. 2008).
Thisconflictingevidenceisperhapsduetotheissueofdrugdosing,ascommonlythebodysurfacearea
(BSA) is capped for obese patients, rather than dosing on actual body weight, thus leading to the
possibilityofunderdosinginobesepatients.ItiswellknownthatBSAisnotpredictiveofdrughandling
in obese patients (Chambers et al. 2011). Indeed, nonrandomized evidence from three trials involving
mCRCpatientssuggestedworseoutcomeswhenreduceddosingwasgiventoobesepatients(Chambers
etal.2011).ThecurrentrecommendationsfromtheAmericanSocietyofClinicalOncology(ASCO)are
forfullweight-baseddosingofchemotherapyinobesepatientswithcancer,particularlywhentreatmentis
with curative intent (Griggs et al. 2012).
Lifestyle Factors
Theprognosticorpredictivevalueoffactorssuchasdiet,exercise,smoking,andalcoholconsumptionis
notwellestablishedinmCRC,despitetheirroleinthedevelopmentofCRCbeingwellknown(Martinez
2005). Exercise is important for CRC patients, with more exercise undertaken leading to a lower risk of
disease recurrence (Meyerhardt et al. 2006). Very heavy smokers have been shown to have a slightly
worse outcome, but smoking in general appears to have negligible impact on outcome (McCleary
et al. 2010). One explanation for the impact of lifestyle factors on cancer outcome is that a different
biology of the tumor is induced, supported by preliminary data suggesting different genetic mutations
caused by smoking and diabetes (Limsui et al. 2010).
Tumor-Related Factors
Microsatellite Instability
CRC is considered a genetic disease characterized by sequential genetic and epigenetic alterations
marking its histological progression. Microsatellite instability (MSI) is a signature borne of inactivation
of the DNA mismatch repair (MMR) system, seen in approximately 15 % of CRC tumors either due to
epigenetic silencing of MLH1 or germline mutation in one of the four MMR genes (Vilar and Gruber
2010).TumorswithhighlevelsofMSI(MSI-H)exhibitadistinctphenotype,beingmorecommonlyright
sided, poorly differentiated, mucin-containing, and occurring most commonly in females. These tumors
are more common in early stage, i.e., stage II, CRC. Yet despite these normally adverse histological
features, MSI-H tumors have a more favorable prognosis and lower risk of recurrence than MSI-low
(MSI-L)ormicrosatellite-stable(MSS)tumors(Popatetal.2005).Inthemetastaticsetting,however,MSI
is associated with poorer survival, driven by its association with BRAF mutation (Tran et al. 2011).
Epithelial Growth Factor Receptor
OverexpressionofEGFRisanegativeprognosticmarkerformCRC,asactivationoftheEGFRpathway
correlates with an aggressive phenotype, with greater proliferation and angiogenesis and reduced
apoptosis. It is also associated with chemotherapy and radiotherapy resistance (reviewed in Markman
et al. (2010)). EGFR is overexpressed in 50–70 % of CRCs.
KRAS and BRAF Mutations
Mutations in KRAS are the most commonly described in the Ras/Raf/MAPK pathway in CRC, with
betweenathirdtoahalfofpatientswithCRCcarryingaKRASmutation(DeMattos-Arrudaetal.2011).
The prognostic significance of KRAS is unclear, with the large RASCAL2 collaborative trial suggesting
that a mutation in codon 12 (glycine to valine) of the KRAS gene had a significant impact on survival in
patients with Dukes C CRC (Andreyev et al. 2001), although this was not confirmed in a large adjuvant
trial(PETACC-3)(Rothetal.2012).SeveralmonotherapytrialsofEGFRmonoclonalantibodies(mAbs)
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versusbestsupportivecarehavealsofailedtoshowKRASstatustobeanimportantprognosticmarkerin
patients receiving best supportive care alone (Karapetis et al. 2008; Amado et al. 2008).
BRAF codes for a downstream effector of KRAS in the Ras/Raf/MAPK pathway, with mutations
identified in 10–15 % of CRC tumors (De Mattos-Arruda et al. 2011), the most common being the
BRAFV600Emutationwhichaccountsfor90%ofallBRAFmutationsinCRC.BRAFV600Eisusually
mutually exclusive of KRAS mutations and is considered to be a poor prognostic marker in CRC with a
moreaggressivephenotype(VanCutsemetal.2011b;Samowitzetal.2005),withevidencefromseveral
studies of a significantly higher cancer-specific mortality and worse OS in patients who are KRAS wild
type(WT)withaBRAFV600Emutation,comparedtothosewhoareBRAFV600EWT(Rizzoetal.2010;
Van Cutsem et al. 2011b).
PIK3CA Mutations
AcomponentofthePI3K/PTEN/AKTpathway,PIK3CAisresponsibleforproducingPI3K,thecatalytic
component of the pathway. Mutations in PIK3CA occur in around 20 % of CRC tumors with KRAS
mutations (Sartore-Bianchi et al. 2009). Loss-of-function mutations of the tumor suppressor PTEN can
also activate the PI3K/AKT pathway, with PTEN loss occurring in around 20–40 % of CRC tumors
(Laurent-Puig et al. 2009). The presence of PIK3CA mutations has been suggested to predict poor
prognosis for mCRC patients (Sartore-Bianchi et al. 2009), and loss of PTEN expression has been
associated with an aggressive phenotype in CRC (Sawai et al. 2008).
Vascular Endothelial Growth Factor
FiftytoseventypercentofCRCsexpressvascularendothelial growthfactor(VEGF);however,itsvalue
asaprognosticmarkerisunclear,withconflictingresultshavingbeenfoundamongstudies.VEGFtumor
expressionhasbeenshowntohavenosignificantprognosticutility(Jubbetal.2006;Khoranaetal.2003),
but it has been shown to correlate with increased microvessel density and poor prognosis (Manley
et al. 2002). Similarly microvessel density has also shown contradictory results, with no prognostic
value demonstrated in the Jubb study (Jubb et al. 2006). VEGF expression has been shown to be
associated with increased median survival when expressed in tumor-associated macrophages/stroma
(Khorana et al. 2003), giving rise to the possibility of a link with the causes and consequences of local
inflammation. The VEGF ligands VEGF-A and -D have demonstrated prognostic value through studies
showingthathighexpressioncorrelateswithtumoraggressivenessandshortenedsurvivaltimes(Kopetz
et al. 2010; Moehler et al. 2008).
Predictive Biomarkers
Predictive biomarkers predict response to treatment, either in the form of outcome or toxicity. Measures
used to describe these include response rates and survival.
Predicting Chemotherapeutic Response and Toxicity
Few biomarkers exist that predict chemotherapy utility or toxicity from therapy. The majority have
generallydemonstratedinconsistencyofresults,oftenduetotechnicalissuesofassayvariability.Table2
liststhechemotherapeuticagentsusedinthetreatmentofCRC,andTable3summarizesfactorsthathave
been assessed as prognostic or predictive of response.
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Table2 AgentsusedinthetreatmentofmCRCandtheirbiologicaltargets
Agents Target Clinicalplace
5-fluorouracil/ InhibitionofTS Established,assingleagentorcombinationregimens
capecitabine/S1
Oxaliplatin NuclearDNA;intrastrandadduct Established,incombinationwith5-FUandleucovorin
formation (FOLFOX)orcapecitabine(CAPOX)
Irinotecan Inhibitionoftopo-1 Established;combinedregimen(FOLFIRI)andsingle-agent
withcetuximab
Cetuximab ChimericIgG1mAbagainstEGFR Establishedincombinationwithirinotecanchemotherapyafter
priortreatment
Panitumumab FullyhumanIgG2mAbagainst Establishedincombinationwithirinotecanchemotherapyafter
EGFR priortreatment
Bevacizumab mAbagainstVEGF-A Establishedasfirst-linetreatmentincombinationwith
chemotherapy
Aflibercept VEGF-A,-B,andplacentalgrowth PhaseIIIRCTevidenceofefficacyafterprevioustreatment
factorinhibitor
Regorafenib Multi-targetedtyrosinekinase PhaseIIIRCTevidenceofefficacyafterprevioustreatment
inhibitoragainstVEGF
Valatinib OralVEGFinhibitor PhaseIIIRCTevidenceofefficacyasfirst-linetreatmentin
combinationwithchemotherapy
Table3 PrognosticandpredictivefactorsforchemotherapyinmCRC
Factor Evidence Utility Reference
MSI Considerable Predictslackofbenefitfrom5-FU DesGuetzetal.2009
TS Insufficient Predictstoxicityfrom5-FU Popatetal.2006;Soong
polymorphisms etal.2008;Koopmanetal.2009b
DPDexpression Inconsistent LowDPDpredictsforgreater5-FUtoxicity Vallbohmeretal.2007;Koopman
etal.2009c
TPexpression Conflicting Evidenceofbothbetterandworseoutcomeand Soongetal.2008;Meropol
responseto5-FU etal.2006
MTHFR Inconsistent Potentialpredictivemarkerfor5-FU Gusellaetal.2009;Ruzzo
polymorphisms etal.2007
ERCC-1variant Insufficient PredictiveofimprovedOSwithTTorCTgenotypes Viguieretal.2005;Moreno
expression withoxaliplatin etal.2006
XPDvariant Inconsistent ImprovedRR,PFS,orOSwithplatinumdrugs LeMorvanetal.2007
expression
GSTP1variant Inconsistent Predictionofoxaliplatinresponse Stoehlmacheretal.2002
expression
GSTP1variant Conflicting Predictionofoxaliplatinneurotoxicity Lecomteetal.2006;Ruzzo
etal.2007
Topo-1 Inconsistent Lowexpressionpotentiallynegativepredictorof Braunetal.2008;Koopman
irinotecanoroxaliplatinresponse etal.2009a
UGT1A1*28 Insufficient Increasedirinotecan-inducedtoxicityandperhaps Iyeretal.2002;Hoskins
allele improvedresponse etal.2007
UGTlocus Insufficient Potentiallypredictiveofirinotecan-inducedtoxicity Innocentietal.2004;Cecchin
etal.2009
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Markers to Predict 5-FU Response and Toxicity
Mismatch repair deficiency is the single predictive marker of chemotherapy response to demonstrate
consistentstudyresults.Inadditiontohavingamorefavorableprognosisandlowerriskofrecurrence,it
has been reported that patients with MSI-H tumors may not benefit from 5-FU-based adjuvant chemo-
therapyduetoalackofsensitivity,withonlyMSSorMSI-Ltumorsbenefitting(DesGuetzetal.2009).
5-FUremainsakeycomponentinCRCtreatment,bothintheadjuvantandpalliativesettings.Itsmain
mechanismofactionisviainhibitionofthymidylatesynthase(TS),whoseexpressionmaybeinfluenced
by genetic variants of the TYMS gene. A significant inverse association between the number of 28-base
pairtandemrepeatsintheTYMSpromoterregionandtheseverityoftoxicityhasbeenfound,althoughthe
sensitivity and specificity is low (Schwab et al. 2008). Studies on TS expression and prognosis in CRC
haveshownhighTSlevels tobeassociatedwithpoorerOS(Popatetal. 2004).Threelargestudieshave
examinedTSexpressioninpatientsreceiving5-FU-basedchemotherapyintheadjuvantsetting,withno
significant association between TS expression and outcome (Popat et al. 2006; Soong et al. 2008;
Koopman et al. 2009b).
The enzymes dihydropyrimidine dehydrogenase (DPD), thymidine phosphorylase (TP), and
methylenetetrahydrofolate reductase (MTHFR) have been examined for their predictive value for 5-FU
chemotherapy.DPDistherate-limitingenzymein5-FUmetabolism,resultingintheformationofinactive
dihydrofluorouracil that is eventually converted to fluoro-beta-alanine for hepatic excretion. Low DPD
expression could cause a decrease in 5-FU catabolism and higher intracellular levels, resulting in
increased neutropenia, stomatitis, and death (Wei et al. 1996). In patients with unexpectedly severe
toxicity after 5-FU treatment, reduced DPD activity was seen in the peripheral mononuclear cells of at
least55%ofpatients(vanKuilenburgetal.2000).However,resultshavenotbeenconsistent.Whilelow
DPDlevelshavebeenassociatedwithlongerdisease-freesurvival(DFS)orOSwithfluoropyrimidineuse
inthemetastaticsetting(Vallbohmeretal.2007;Koopmanetal.2009c),thereversehasalsobeenfound
(Meropol et al. 2006).
TPisinvolvedintheconversionof5-FUtoitsactivemetaboliteFdUMPanditispostulatedthathigh
levels result in better outcomes and responses. However, high TP levels may also confer a poorer
outcome, given that TP is also known as platelet-derived endothelial cell growth factor (PD-ECGF),
which has been associated with angiogenesis (Matsumura et al. 1998) and positively correlates with
microvessel density (Matsuura et al. 1999). Not surprisingly, conflicting evidence exists regarding the
utility of TP as a prognostic or predictive marker (Soong et al. 2008; Koopman et al. 2009b; Meropol
et al. 2006).
MTHFRisthemainenzymeinvolvedintheconversionof5,10-methylenetetrahydrofolate,ascomplex
crucial in the activity of 5-FU; MTHFR polymorphisms responsible for 5,10-methylenetetrahydrofolate
couldthereforeplayanimportantroleinthecytotoxicityof5-FU.Whilenumerousstudieshaveexamined
this issue, the results have been inconsistent (Gusella et al. 2009; Chua et al. 2009; Capitain et al. 2008;
Ruzzo et al. 2007).
Markers to Predict Oxaliplatin Response and Toxicity
Oxaliplatin (PtCl (1,2-diaminocyclohexane (DACH)]) exerts its cytotoxic effect primarily through for-
2
mationofintrastrandDNAadducts,leadingtoinhibitionofDNAreplicationandinductionofapoptosis.
Genetic variants such as single-nucleotide polymorphisms (SNPs) in genes involved in any of the DNA
repairpathwaysmayaccountfordifferencesinindividualresponsesortoxicitytooxaliplatinchemother-
apy, but so far, no consistently useful biomarker has been found.
The excision repair cross-complementing group 1 (ERCC-1) and xeroderma pigmentosum comple-
mentationgroupD(XPDorERCC-2)proteinsareinvolvedinthenuclearexcisionrepair(NER)pathway.
ERCC-1 SNPs or protein expression has failed to demonstrate clinical utility in prediction of outcome
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fromoxaliplatinregimensinmCRC.ThesynonymousERCC1variantAsn118Asn(C > T,rs11615)has
shown improved RR or survival for mCRC patients with the TT (homozygous mutant type) or CT
genotype when compared to patients with the CC genotype (homozygous wild type) (Viguier
et al. 2005; Moreno et al. 2006), while other studies have found patients with the Tallele to have worse
survival or disease progression (Chua et al. 2009; Ruzzo et al. 2007; Stoehlmacher et al. 2004). An
association between low ERCC1 mRNA and protein expression with improved survival was seen in
several small studies (Shirota et al. 2001; Kim et al. 2009) but not in two recent large randomized
controlledtrials(RCTs)(Koopmanetal.2009c;Braunetal.2008).Similarlythexerodermapigmentosum
genes have failed to demonstrate consistency with the ERCC2 missense variant Lys751Gln (rs13181)
havingdemonstratedanassociationwithimprovedRR,event-freesurvival,orPFSandOSwithplatinum
drugs in some studies (Park et al. 2001; Le Morvan et al. 2007) but not in others (Moreno et al. 2006;
Braun et al. 2008).
X-rayrepaircross-complementingprotein1(XRCC-1)isinvolvedinDNArepairviathebase-excision
repair pathway.XRCC1 polymorphismshavebeeninvestigated but generally not shown anyassociation
with outcome or toxicity (Chua et al. 2009; Ruzzo et al. 2007; Braun et al. 2008, 2009; Stoehlmacher
et al. 2004). Similarly, detrimental effects of the missense variant Gln399Arg (rs25487) were seen on
responserate(RR)inalargecase–controlstudy(Suhetal.2006)butwithimprovedprognosisforpatients
treated adjuvantly (Moreno et al. 2006).
Glutathione-S-transferase (GST) facilitates platinum-DACH binding to glutathione, with this new
complex preventing platinum/DNA binding and thus rendering the platinum compound inactive
(Kweekel et al. 2005). The missense variant Ile105Val (rs1695) in GSTP1 has been investigated for its
utility as a biomarker, given that it produces a variant GSTP1 protein that has demonstrated decreased
ability to detoxify carcinogens (Kweekel et al. 2005); however, results have been inconsistent.
A statistically significant reduction in the risk of death from advanced CRC has been shown for patients
possessing the Ile105Val variant, with the greatest benefit being for those homozygous for Ile105Val
(Stoehlmacheretal.2002);however,subsequentstudiesfailedtoshowasignificantassociationbetween
the Ile105Val variant or protein expression and survival or tumor response (Ruzzo et al. 2007; Braun
et al. 2008; Kweekel et al. 2009). The influence of GSTP1 variant on oxaliplatin-induced neurotoxicity
hassimilarlybeenconflicting,withnoinfluenceon(Kweekeletal.2009),increased(Ruzzoetal.2007),
and decreased (Lecomte et al. 2006) severe neuropathy all having been associated.
Markers to Predict Irinotecan Response and Toxicity
Irinotecan,acamptothecinanalog,isconvertedtoSN-38intheliver,whichinhibitsthetopoisomerase-1
(topo-1) enzyme and eventually inhibits DNA replication and transcription. Topo-1 is overexpressed in
>40 % of CRCs (Paradiso et al. 2004), but its predictive value is inconclusive. Topo-1 was found to be
predictiveofoutcomeinastudyofadvancedCRCexaminingsequentialversuscombinationchemother-
apy, with patients with low levels of Topo-1 failing to derive a benefit from irinotecan or oxaliplatin
combinations, while patients with high Topo-1 levels did better with combination rather than sequential
treatment with longer median survival (Braun et al. 2008). However, validation of these results with the
CAIRO study failed, with no correlation found between Topo-1 levels and OS (Koopman et al. 2009a).
Uridine-diphosphoglucuronosyltransferase(UGT)istheenzymeresponsibleforeliminationofSN-38
byglucuronidation.ItisencodedbytheUGT1A1genewithitsactivityrelatedtothenumberofTArepeats
inthepromoterregionofeachallele.PatientshomozygousfortheUGT1A1*28allelehavebeenshownto
haveincreasedSN-38concentrationsduetodecreasedenzymelevels(Iyeretal.1998),sotherelationship
between UGT1A1*28 and irinotecan-induced toxicities has been investigated with inconsistent results.
Patients with UGT1A1*28/*28 genotype have demonstrated increased hematological toxicity requiring
lower irinotecan starting doses, together with perhaps improved responses (Iyer et al. 2002; Liu
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