Test Center

My Recent Searches

  • No Recent Search.

My Tests Viewed

  • No Test Viewed.

Colorectal Cancer Mutation Panel (KRAS, PIK3CA, BRAF, NRAS)

Colorectal Cancer Mutation Panel (KRAS, PIK3CA, BRAF, NRAS)

Test Summary

Colorectal Cancer Mutation Panel
(KRAS, PIK3CA, BRAF, NRAS)

  

Clinical Use

  • Predict response to EGFR-targeted immunotherapy in patients with metastatic colorectal cancer

Clinical Background

Multiple signaling pathways are involved in colorectal cancer pathogenesis. The epidermal growth factor receptor (EGFR) plays a key role in activation of these pathways and is commonly overexpressed in metastatic colorectal cancer (mCRC). Consequently, EGFR is a target of anti-cancer therapies. Two of these drugs, cetuximab and panitumumab, are monoclonal antibodies that block EGFR action. These EGFR immunotherapies, however, are not effective if downstream signaling pathways are activated independent of EGFR; such is the case when gene mutation causes overexpression of enzymes in these pathways. Thus, detecting mutations that lead to activation of signaling pathways downstream from EGFR can predict resistance to EGFR immunotherapy.

For example, KRAS, BRAF, or NRAS mutations can all activate the RAS-RAF-MAPK pathway, which is downstream from EGFR. In chemotherapy-refractory patients, fewer than 10% of patients who harbor 1 of these mutations respond to EGFR immunotherapy.1,2 The American Society of Clinical Oncology (ASCO) and the National Comprehensive Cancer Network (NCCN) both recommend KRAS mutation testing prior to prescribing EGFR antagonist therapy for patients with mCRC and state that alternative therapy should be prescribed when mutations are detected.3,4 When KRAS is mutation-negative, the NCCN suggests considering BRAF mutation testing.4

PIK3CA mutations activate the PI3K-PTEN-AKT pathway which is downstream from both the EGFR and the RAS-RAF-MAPK pathways. PIK3CA mutations have been associated with resistance to anti-EGFR therapy in some studies2,5 but not in others.6,7 The reasons for the discrepancy are not clear.

Mutation Profiling

PIK3CA mutations may overlap with mutations in BRAF, KRAS, and NRAS,2 but BRAF, KRAS, and NRAS mutations are almost always mutually exclusive (ie, mutations in only 1 of the 3 genes occur within any individual tumor). These facts suggest that mutation analysis of all 4 of these genes could be clinically useful. Indeed, studies support mutation profiling in CRC tumors: 1) Response rate improved from 24% in cetuximab-treated patients whose mutation status was unknown to 41% in patients who tested negative for mutations in all 4 genes (response rates and outcomes are summarized in the Table)2; and 2)  objective response, progression-free survival (PFS), and overall survival (OS) were progressively worse when 0, 1, and 2 mutations were present in patients treated with either cetuximab or panitumumab.8 Thus, mutation profiling can effectively select patients who are more likely to respond to anti-EGFR immunotherapy, rule out this treatment for those who are not likely to respond, and predict patient outcomes.2,4,8

Table. Effect of Oncogene Mutations on Patients with Metastatic Colorectal Cancer Treated with Cetuximab and Chemotherapy2
Oncogene Prevalence,
%
Objective Responsea, % Median Progression-
free Survival, Weeks
Median Overall
Survival, Weeks
Mutation
Negative
Mutation
Positive
Mutation
Negative
Mutation
Positive
Mutation
Negative
Mutation
Positive
KRAS 40 36 7 24 12 50 32

PIK3CAb

15 38 18 24

18c

51

39c

BRAFb

5 38 8 26 8 54 26

NRASb

3 38 8 26

14c

50

38c

a Objective response includes complete or partial response using RECIST or WHO criteria.
b KRAS-mutation negative.
c Not statistically significant.

The Quest Diagnostics Colorectal Cancer Mutation Panel includes testing for gene mutations in both EGFR downstream signaling pathways and thus provides increased ability to predict sensitivity or resistance to cetuximab or panitumumab versus single pathway or single gene testing. Although less data are available for panitumumab than for cetuximab, common molecular resistance pathways support mutation profile testing for both drugs.9 Individual tests for mutation detection are also available for each gene.

Individuals Suitable for Testing

  • Patients with colorectal cancer who are candidates for cetuximab or panitumumab therapy

Method

  • Polymerase chain reaction (PCR) amplification of

   Exon 1 (codons 12 and 13) and exon 2 (codon 61) of the KRAS and NRAS genes

   Exon 1, exon 9 (codon 545), and exon 20 (codon 1047) of the PIK3CA gene (targets >95% of known

mutations)

   Exons 11, 12, and 15 (codon 599/600) of the BRAF gene (targets >99% of known mutations)

  • Forward and reverse, dye-terminator gene sequencing of purified products

  • Analytical sensitivity: 10% tumor cells in the background of normal cells. Testing is performed on sample where tumor is enriched.

Interpretive Information

Mutation in any 1 of the 4 genes is associated with resistance to cetuximab and panitumumab (Figure).

Figure. Mutation testing results predict response to anti-EGFR immunotherapy in patients with metastatic colorectal cancer.

KRAS, BRAF, or NRAS mutations are associated with shorter PFS and OS in patients treated with anti-EGFR immunotherapy relative to those who are mutation-negative.2,6 BRAF mutations are negative prognostic indicators irrespective of therapy.6

Polymorphisms or mutations at locations not tested (see “Method”) that may be associated with drug efficacy or patient outcome will not be detected. Results should be interpreted in conjunction with other laboratory and clinical findings.

References

  1. Heinemann V, Stintzing S, Kirchner T, et al. Clinical relevance of EGFR- and KRAS-status in colorectal cancer patients treated with monoclonal antibodies directed against the EGFR. Cancer Treat Rev. 2009;35:262-271.

  2. DeRoock W, Claes B, Bernasconi D, et al. Effects of KRAS, BRAF, NRAS, and PIK3CA mutations of the efficacy of cetuximab plus chemotherapy in chemotherapy-refractory metastatic colorectal cancer: A retrospective consortium analysis. Lancet Oncol. 2010;11:753-762.

  3. Allegra CJ, Jessup JM, Somerfield MR, et al. American Society of Clinical Oncology provisional clinical opinion: testing for KRAS gene mutations in patients with metastatic colorectal carcinoma to predict response to anti-epidermal growth factor receptor monoclonal antibody therapy. J Clin Oncol. 2009;27:2091-2096.

  4. Engstrom PF, Arnoletti JP, Benson AB, et al. NCCN Clinical Practice Guidelines in Oncology™: colon cancer. National Comprehensive Cancer Network Web site. http://www.nccn.org/professionals/physician_gls/
    PDF/colon.pdf . Version 3. 2010. Accessed September 9, 2010.

  5. Sartore-Bianchi A, Martini M, Molinari F, et al. PIK3CA mutations in colorectal cancer are associated with clinical resistance to EGFR-targeted monoclonal antibodies. Cancer Res. 2009;69:1851-1857.

  6. Tol J, Dijkstra JR, Klomp M, et al. Markers for EGFR pathway activation as predictor of outcome in metastatic colorectal cancer patients treated with or without cetuximab. Eur J Cancer. 2010;46:1997-2009.

  7. Prenan H, DeSchutter J, Jacobs B, et al. PIK3CA mutations are not a major determinant of resistance to the epidermal growth factor inhibitor cetuximab in metastatic colorectal cancer. Clin Cancer Res.2009;15:3184-3188.

  8. Sartore-Bianchi A, Di Nicolantonio F, Nichelatti M, et al. Multi-determinants analysis of molecular alterations for predicting clinical benefit to EGFR-targeted monoclonal antibodies in colorectal cancer. Plos One. 2009;4:e7287.

  9. Bardelli A, Siena S. Molecular mechanisms of resistance to cetuximab and panitumumab in colorectal cancer. J Clin Oncol. 2010;28:1254-1261.
     

This test was developed and performance characteristics have been determined by Quest Diagnostics Nichols Institute. Performance characteristics refer to the analytical performance of the test.

Content reviewed 12/2011
 
top of page

* The tests listed by specialist are a select group of tests offered. For a complete list of Quest Diagnostics tests, please refer to our Directory of Services.