2012 EDUCATIONAL BOOK - American Society of Clinical Oncology

Table 1. Tumor Marker Utility Grading System Levels of
Evidence
Level Definition
I Prospective, marker primary objective
Well-powered or meta-analysis
II Prospective, marker the secondary objective
III Retrospective, outcomes, multivariate analysis (most currently published
marker studies are level of evidence III)
IV Retrospective, outcomes, univariate analysis
V Retrospective, correlation with other marker, no outcomes
Adapted with permission from Hayes DF, Bast RC, Desch CE, et al. Tumor
marker utility grading system: a framework to evaluate clinical utility of tumor
markers. J Natl Cancer Inst. 1996;88:1464.
been well established, the 20% to 40% of colon cancers
lacking PTEN expression as a result of promoter methylation
would be expected not to respond to EGFR inhibition.
The same applies to tumors with activated PI3K, which
again is downstream of ligand signaling through the EGFR
and could explain why so few patients with wild-type KRAS
and BRAF fail to benefit from EGFR inhibition. Figure 2
(from Dienstmann, Vilar, and Tabernero 27 ) describes the
possible abnormalities that can account for resistance to
EGFR antibodies.
Gene Expression Arrays
There are numerous papers describing the correlation
between gene expression and prognosis in colorectal cancer.
Although Oncotype Dx (Genomic Health, Inc., Redwood
City, CA) and Coloprint (Agendia, Irvine, CA) have been
commercialized and are available for purchase, a number of
other investigators have reported, tested, and subsequently
validated mRNA arrays as prognostic tools in colon cancer.
In 2004, Wang and colleagues 32 reported a 23-gene signature
based on the Affymetrix (Santa Clara, CA) Gene Chip
that accurately predicted relapse in stage II colon cancers.
Eschrich and colleagues as well as Arango 33,34 reported in
2005 that a 43-gene signature predicted recurrence in stage
II and III colon cancer. Barrier and colleagues in 2006
identified a 30-gene signature using mRNA microarrays
that predicted outcome in stage II colon cancer 35 In 2007,
Gray and colleagues 36 reported the first experience using a
set of 761 genes assayed by reverse transcriptase polymerase
chain reaction (RT-PCR) to develop a signature for
colon cancer recurrence, and this evolved in Oncotype Dx
into a validation study in 2011. 37,38 The diagnostics company
Almac (Souderton, PA) used a 634-probe set signature
(Col Dx) 39 to identify patients with colon cancer with a high
risk of recurrence in stage II colon cancers that is undergoing
multiple independent validation studies. And in 2011,
Salazar and colleagues demonstrated and validated the
utility of an 18-gene signature, originally described in 2007,
and is now commercially available 40,41 and sold as Coloprint
for colon cancer prognosis. Febbo and colleagues identified
levels of evidence for marker studies and NCCN categories
of evidence. 24 Level 1 is used to characterize markers that
were evaluated prospectively where the marker was the
primary objective of the study. Most of the markers in the
literature fall under Level IV, in which evaluation was
retrospective and outcomes were determined in univariate
analysis. Most of the array-based and RT-PCR–based
genomic signatures fall under this category, including Colo-
Print and Oncotype Dx. Interestingly, none of these arraybased
signatures was informative in terms of response to
chemotherapy. Also, there is very little overlap in the set of
genes chosen to create a prognostic signature in colon
cancer, even though it seems that risk assessment is comparable
regardless of the platform used. Choosing the best
platform involves consideration of cost, rapidity of turnover,
reproducibility, and whether any of these gene expression
signatures have been assessed in multivariate analysis with
other potential markers of outcome (p53 mutational status,
p27 loss, thymidylate synthase expression, microsatellite
instability, and others). Consequently, although available to
the clinician and the patient, the exact utility of gene
expression signatures remains a subject of debate. Neither
Oncotype Dx nor ColoPrint is included in the NCCN guidelines
for colon cancer.
p53: When Genotype Interacts with Gender and
Chemotherapeutic Regimen
Table 2. Pair-Wise Comparisons of Survival by p53 Mutational Status
The p53 tumor suppressor is frequently mutated in colon
cancer, but the influence of such mutations on survival is
still controversial 42 p53 mutations have been inferred by
positive staining using IHC since the wild-type protein is
degraded very rapidly, and is not demonstrable in the
nucleus by immunohistochemistry, although the gold standard
for p53 mutation analysis is Sanger sequencing. We
investigated whether DNA-binding domain-specific mutations
in p53 are predictive of survival in stage III colon
cancer. p53 was evaluated in an intergroup trial, CALGB
89803, 43 in patients with stage III colon cancer who were
randomly assigned to receive adjuvant FU/LV or FU/LV
with IFL, and various molecular markers were correlated
with outcomes. p53 was genotyped in 607 patient tumors:
p53 mutations were identified in 274 tumors, divided
equally between zinc-binding and non–zinc-binding regions
of the DNA-binding domain. Overall, p53 status was not
predictive of benefit from either adjuvant regimen. Unexpectedly,
however, the 5-year OS of women with tumors
harboring non–zinc-binding mutations treated with FU/LV
was 97% compared with OS of 72% for women with p53
wild-type tumors (p � 0.004). Adding IFL to FU/LV negated
this survival benefit (5-year OS of 81% vs. 72%). Conversely,
5-year OS of women harboring tumors with zinc-binding
Wild-Type vs. Zinc Binding Wild-Type vs. Non–Zinc Binding Zinc Binding vs. Non–Zinc Binding
Patient Subset P OS DFS P OS DFS P OS DFS
Men 0.58 0.28 0.19 0.18 0.48 0.7
Women, FU/LV 0.04 0.24 0.004 0.002 �0.001 �0.001
Women, IFL 0.71 0.79 0.18 0.53 0.49 0.83
Men, FU/LV 0.48 0.66 0.80 0.48 0.35 0.29
Men, IFL 0.12 0.05 0.10 0.24 0.85 0.63
Abbreviations: DFS, disease-free survival; FU, fluorouracil; IFL, irinotecan; LV, leucovorin; OS, overall survival.
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VENOOK, BENDELL, AND WARREN