This year saw the introduction of the first commercially
available multiparameter gene profile assay for predicting risk of
recurrence of colon cancer after surgery. The Oncotype DX
colon cancer assay (Genomic Health) for predicting risk of
recurrence in patients with stage II disease was launched in
January 2010, and the ColoPrint assay (Agendia) is likely to be
available soon. Methods for better quantifying risk of recurrence
after surgery in patients with stage II disease are needed, because
patients at higher risk of recurrence may experience a relatively
greater benefit from adjuvant chemotherapy. Such treatment is
associated with only a small absolute survival benefit in this
setting, while posing a risk of toxicity in all who receive it.
Oncotype DX
Like the Oncotype DX
breast cancer assay, the Oncotype DX colon cancer assay
uses real-time reverse transcription polymerase chain reaction
(RT-PCR) technology to measure levels of select cancer-related
genes compared with reference genes. RNA is extracted from manually
microdissected formalin-fixed, paraffin-embedded tumor tissue, and
DNase I treatment is used to eliminate DNA contamination (Fig. 1).
RT-PCR is performed to quantify expression of seven cancer-related
genes, and expression is normalized to expression of a set of five
reference genes, providing the basis for calculating a recurrence
score (0-100). The seven cancer-related genes (Ki-67,
C-MYC, MYBL2, FAP, BGN,
INHBA, GADD45B) include cell-cycle and stromal
genes that were consistently associated with a recurrence-free
interval in development studies.
The availability of high-throughput RT-PCR made it possible to
evaluate 761 candidate genes in samples from 1,851 patients in four
colon cancer treatment studies. The seven genes used in the assay
were selected from among 76 showing statistical associations with
recurrence in these studies. In a validation study involving 1,436
patients with stage II disease, the continuous recurrence
score was significantly and nearly linearly associated with
recurrence risk (P = .004). The 3-year recurrence risk
ranged from 9% to 11% at low recurrence score (< 30, 44% of
patients) to 25% to 27% at high recurrence score (≥ 41, 26% of
patients). On multivariate analysis, recurrence score, T stage, and
mismatch repair (MMR) status were the most important independent
predictors of recurrence.
ColoPrint
Like the Agendia MammaPrint breast cancer assay, the ColoPrint
assay uses DNA microarray technology to determine levels of
expression of cancer-related genes in fresh frozen tumor samples.
In development studies, gene expression in frozen tumor tissue from
188 colon cancer patients with stage I to III disease was
measured on Agilent 44K Whole Genome oligonucleotide microarrays.
Multivariate analysis identified a 38-gene signature associated
with risk of development of distant metastases.
The signature was validated in an independent group of 178
stage II or III samples and in in-silico data sets (n =
322). In the validation study, patients identified by the ColoPrint
signature as high-risk (39% of patients) had a significantly
greater risk of distant metastases (HR = 3.2, P =
8.5e-4) compared with low-risk patients (61% of
patients). The 5-year distant metastasis-free survival rate was 89%
for low-risk patients and 62% for high-risk patients. Prediction of
recurrence with the ColoPrint signature was significant in both
stage II disease (P = .0058) and stage III disease
(P = .036). Multivariate analysis showed the signature to
be the most prognostic factor. To make the test suitable for
clinical use, the profile was translated into a diagnostic test
using an Agilent 8-pack format that supports high throughput.
These assays help to refine risk of recurrence in early-stage
colon cancer. For the present, their optimal use in selecting
patients for adjuvant chemotherapy is in combination with
established clinicopathologic factors. ■
Additional Resources on Oncotype
DX
Kerr D, Gray R, Quirke P, et al: A quantitative multigene RT-PCR
assay for prediction of recurrence in stage II colon cancer:
Selection of the genes in four large studies and results of the
independent, prospectively designed QUASAR validation study 2009
ASCO Annual Meeting. Abstract 4000. Abstract presented May 31,
2009.
Glas AM, Roepman P, Salazar R, et al: Development and validation
of a robust prognostic and predictive signature for colorectal
cancer (CRC) patients. 2009 ASCO Annual Meeting. Abstract 4036. Abstract presented May 30,
2009.
Additional Resources on ColoPrint
Salazar R, Marshall J, Stork-Sloots L, et al: The PARSC trial, a
prospective study for the assessment of recurrence risk in stage II
colon cancer (CC) patients using ColoPrint. 2010 ASCO Annual
Meeting. Abstract TPS199. Poster presented June 7,
2010.
Rosenberg R, Maak M, Nitsche U, et al: Independent validation of a
prognostic genomic profile (ColoPrint) for stage II colon cancer
(CC) patients. 2010 ASCO Annual Meeting. Abstract 3513. Poster presented June 8,
2010.
