The State of the Art in Colorectal Cancer Molecular Biomarker Testing

Abstract

The number of molecular biomarkers to inform treatment decisions in patients with metastatic colorectal cancer (mCRC) continues to expand and with it the methodologies that can be employed to evaluate these biomarkers. Beyond standard diagnostic and prognostic biomarkers, such as those used for Lynch syndrome, mutations in KRAS exon 2 are well established as predictive for lack of response to the antiepidermal growth factor receptor therapies panitumumab and cetuximab. Recent studies have extended these findings by demonstrating that mutations in KRAS exons 3 and 4 and in NRAS exons 2, 3, and 4 (with all KRAS and NRAS mutations collectively referred to as RAS) are also predictive for treatment outcomes among patients with mCRC receiving panitumumab and cetuximab in combination with chemotherapy or as monotherapy. Consequently, evaluation of these additional loci has been incorporated into current clinical guidelines, and pathologists will need to develop testing procedures and algorithms to reliably and rapidly evaluate RAS status. With the increased number of mutations that must be examined to evaluate the status of RAS and other emerging biomarkers, next-generation sequencing technologies are likely to become increasingly important in mCRC testing. This review describes new considerations for pathologists that have arisen as a consequence of the incorporation of additional biomarker testing into clinical practice for mCRC.

Figure 1

IHC and MSI initial tumor screening strategies vary by institution; IHC and/or MSI is acceptable. Similarly, BRAF V600E and MLH1 promoter hypermethylation testing strategies vary by institution; BRAF V600E and/or MLH1 promoter hypermethylation is acceptable. *Further work-up for hereditary conditions may still be appropriate if other personal or family history features are present (ie, early age of onset, polyposis, hamartomas, strong family history of cancer, etc). ^†In the case of IHC protein loss of only PMS2, MSH2, or MSH6, germline testing could first be completed for the specific protein lost, and then if negative, proceed to the protein partner pair or full MMR panel testing. ^‡Prior to germline testing (blood or saliva), appropriate pretest counseling should be completed by an individual with hereditary clinical genetics expertise. ^§Somatic MMR sequencing has shown that tumors can have biallelic loss of MMR genes, loss of heterozygosity; false positive MMR tumor testing may also be causative (see text).

Figure 2

Role of RAS enzymes in the EGFR signaling pathway. RAS=KRAS/NRAS. Reprinted with permission from Siddiqui AD, Piperdi B. KRAS mutation in colon cancer: a marker of resistance to EGFR-I therapy. Ann Surg Oncol 2010;17:1168-1176.

Figure 3

Hazard ratios for (A) disease progression or (B) death by KRAS and RAS mutation status in patients with mCRC treated with panitumumab + FOLFOX-4 and FOLFOX-4 alone in PRIME. FOLFOX-4=fluorouracil, leucovorin, and oxaliplatin; PRIME=Panitumumab Randomized Trial in Combination With Chemotherapy for Metastatic Colorectal Cancer to Determine Efficacy; RAS=rat sarcoma-2 virus oncogene. Reprinted with permission from Douillard JY, Oliner KS, Siena S, et al. Panitumumab-FOLFOX4 treatment and RAS mutations in colorectal cancer. N Engl J Med. 2013;369:1023-1034.

Figure 4

The EGFR signaling network. Reprinted with permission from Chong CR, Jänne PA. Nature Med. 2013;19:1389-1400.

Figure 5

Role of pathologists in conducting and reporting RAS analysis in patients with mCRC.