Genomic Profiling for KRAS, NRAS, BRAF, Microsatellite Instability, and Mismatch Repair Deficiency Among Patients With Metastatic Colon Cancer

Martin E. Gutierrez, MD; Kristin S. Price, MS; Richard B. Lanman, MD; Rebecca J. Nagy, MS; Irfan Shah, BBA; Shivam Mathura, BA; Michael Mulcahy, BS; Andrew D. Norden, MD, MPH, MBA; Stuart L. Goldberg, MD

Disclosures

JCO Precis Oncol. 2019;3 

In This Article

Abstract and Introduction

Abstract

Purpose: Genomic testing is recognized in national guidelines as essential to guide appropriate therapy selection in metastatic colorectal cancer. Previous studies report adherence to testing guidelines is suboptimal, but current testing rates have not been assessed. This study reports testing rates in metastatic colon cancer (mCC) for guideline-recommended biomarkers in a US-based population.

Materials and Methods: A retrospective review of data extracted from electronic medical records was performed to identify patients with pathologically confirmed mCC and describe patterns of guideline-aligned biomarker testing. Data were extracted from the electronic health records of 1,497 patients treated at 23 practices across the United States. Both community and academic centers were represented.

Results: A total of 1,497 patients with mCC diagnosed between January 1, 2013 and December 31, 2017 were identified. Guideline-aligned biomarker testing rates for RAS, BRAF, and microsatellite instability/mismatch repair deficiency over this study period were 41%, 43%, and 51%, respectively. Patients were more likely to have guideline-aligned testing for RAS and BRAF if they were treated at an academic center, were diagnosed with de novo metastatic disease, and were female. In addition, patients < 65 years of age were more likely to have guideline-aligned RAS testing. Of the 177 patients (12% of cohort) who received anti–epidermal growth factor receptor therapy, only 50 (28%) had complete guideline-aligned biomarker testing.

Conclusion: Despite guideline recommendations and significant therapeutic implications, overall biomarker testing rates in mCC remain suboptimal. Adherence to guideline-recommended biomarker testing would potentially reduce exposure to expensive and ineffective therapies, resulting in improved patient outcomes.

Introduction

The promise of precision oncology requires the application of biomarker testing to direct appropriate clinical care. Among patients with metastatic colorectal cancer (mCRC), genomic profiling may identify somatic mutations that are prognostic for outcomes and/or predictive of response to approved treatments. In 2009, ASCO and the National Comprehensive Cancer Network (NCCN) published guidelines recommending that patients with mCRC undergo testing for activating mutations in codons 12 and 13 of KRAS exon 2 on the basis of data that patients with these mutations do not derive clinical benefit from the anti–epidermal growth factor receptor (anti-EGFR) monoclonal antibody (MAb) therapies cetuximab and panitumumab.[1,2]KRAS exon 2 mutation testing allows oncologists to avoid the use of ineffective anti-EGFR therapy in approximately 40% of patients with mCRC who may otherwise receive these drugs as second-line therapy.[3]

Over the subsequent 10 years, biomarker testing guidelines have been expanded (Figure 1). Testing for mutations in KRAS exons 3 or 4 and NRAS exons 2, 3, or 4 finds 20% more RAS mutations than exon 2 testing alone, adding another 8% of patients with mCRC who will have poor responses to anti-EGFR therapy (Figure 2).[3,4]BRAF mutations, specifically V600E, predict lack of response to cetuximab and panitumumab in another 9%.[5,6]ERBB2 (HER2) amplification, present in approximately 2% of mCRC, is also a negative predictor of anti-EGFR MAb response, increasing the percentage of patients with mCRC in whom these ineffective agents could be avoided to almost 60%.[7,8]

Figure 1.

Evolution of guidelines for molecular testing in metastatic colorectal cancer (mCRC). FU, fluorouracil; IHC, immunohistochemistry; MMR, mismatch repair; MSI, microsatellite instability; MSI-H, microsatellite instability high; NCCN, National Comprehensive Cancer Network; NGS, next-generation sequencing; pts, patients; wt, wild type.

Figure 2.

Prevalence of negative predictors to anti-EGFR therapy. (A) Frequency of mutations identified in expanded RAS testing.4,20,21 (B) Approximately 60% of patients with metastatic colorectal cancer (mCRC) will have a genetic alteration that may predict poor response to anti-EGFR monoclonal antibody (MAb) therapies cetuximab and panitumumab. Most of these nonresponders will have KRAS exon 2 mutations, but expanded RAS, BRAF, and ERBB2 analysis identifies an additional 20% of patients who will not benefit from therapy.

In addition to their clinical utility as negative predictors of cetuximab and panitumumab response, BRAF mutations and HER2 overexpression are positive predictors of response to targeted therapy. Guidelines recommend targeting both BRAF V600E and HER2-positive (RAS wild type) patients with combination targeted therapies, which have demonstrated durable response and disease control rates in these specific populations.[9–12]

Microsatellite instability (MSI) is an important predictive biomarker for response to immune checkpoint blockade (ICB).[13,14] In 2018, the tumor-agnostic approval of pembrolizumab for the treatment of patients with unresectable or metastatic MSI high (MSI-H) solid tumors after progression on prior approved therapies established this critical biomarker to guide ICB therapy selection.[15] It is also an important screening test for the hereditary cancer syndrome, Lynch syndrome, and a prognostic marker in stage II CRC. The NCCN recommended mismatch repair deficiency (dMMR) testing (by MSI or immunohistochemistry [IHC]) for all patients > 50 years of age in 2011, and then for patients with mCRC at any age in 2015.[16,17]

Although biomarker testing has been advocated for a decade in mCRC guidelines, published testing rates remain low. Carter et al[18] reported 47.5% of patients with mCRC diagnosed between 2008 and 2011 had KRAS testing. A population-based study of > 20,000 patients in the SEER database reported only 30% of patients diagnosed with mCRC in 2010 were tested for KRAS.[19] Shaikh et al[20] reported 28.2% of patients diagnosed with mCRC between 2010 and 2012 had testing for dMMR.

We hypothesize that genomic testing rates for guideline-recommended biomarkers have improved over time. To our knowledge, the current study is the first to report on undergenotyping rates and trends for all four guideline-recommended biomarkers in metastatic colon cancer (KRAS, NRAS, BRAF, and MSI/dMMR) and to characterize the tissue-based methodologies used in real-world practice settings.

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