KRAS and BRAF mutations in circulating tumour DNA from locally advanced rectal cancer

Abstract

There are limited data on circulating, cell-free, tumour (ct)DNA analysis in locally advanced rectal cancer (LARC). Digital droplet (dd)PCR was used to investigate KRAS/BRAF mutations in ctDNA from baseline blood samples of 97 LARC patients who were treated with CAPOX followed by chemoradiotherapy, surgery and adjuvant CAPOX ± cetuximab in a randomised phase II trial. KRAS mutation in G12D, G12V or G13D was detected in the ctDNA of 43% and 35% of patients with tumours that were mutant and wild-type for these hotspot mutations, respectively, according to standard PCR-based analyses on tissue. The detection rate in the ctDNA of 10 patients with less common mutations was 50%. In 26 cases ctDNA analysis revealed KRAS mutations that were not previously found in tissue. Twenty-two of these (84.6%) were detected following repeat tissue testing by ddPCR. Overall, the ctDNA detection rate in the KRAS mutant population was 66%. Detection of KRAS mutation in ctDNA failed to predict prognosis or refine patient selection for cetuximab. While this study confirms the feasibility of ctDNA analysis in LARC and the high sensitivity of ddPCR, larger series are needed to better address the role of ctDNA as a prognostic or predictive tool in this setting.

Analysis of KRAS, NRAS, BRAF, PIK3CA and TP53 mutations in a large prospective series of locally advanced rectal cancer patients

“…47 On the other hand, sampling errors may account for the few remaining "false-negative" (i.e., wildtype) biopsy cases and highlight the potential value of multiple sampling at baseline as well as further investigation and validation of circulating tumour DNA mutational analyses. 49 The results of our analysis should be interpreted with extreme caution due to a number of limitations. The PAN-EX study was meant to analyse all mutational data that were obtained over time from samples of patients included in two prospective trials, this inevitably resulting in the use of several analytic platforms.…”

“…As previously shown, the rate of discordance can be significantly reduced by analysing posttreatment resection samples with more sensitive detection techniques than those used for diagnostic purposes on the pretreatment biopsy . On the other hand, sampling errors may account for the few remaining “false‐negative” (i.e., wild‐type) biopsy cases and highlight the potential value of multiple sampling at baseline as well as further investigation and validation of circulating tumour DNA mutational analyses …”

Temporal and spatial effects and survival outcomes associated with concordance between tissue and blood KRAS alterations in the pan‐cancer setting

“…Blood‐derived ctDNA may provide valuable molecular data as an adjunct to the tumor biopsy for the following reasons: ( i ) tumor biopsies can be complicated procedures with morbidity; ( ii ) some tumors are not readily accessible for biopsy; ( iii ) tissue biopsies can be expensive; ( iv ) as time elapses, the tissue that was biopsied may become less representative of the tumor, since cancers evolve; ( v ) genomics performed on a tissue biopsy reflects the alterations that are in the small tissue specimen, while genomics performed on ctDNA may reflect alterations found in shed DNA from multiple metastatic sites; and ( vi ) dynamic changes in ctDNA can occur and reflect response to therapy or emergence of resistance. In addition, interrogating ctDNA before or after surgery may provide a predictive tool for risk of recurrence . There are also disadvantages to ctDNA as compared to tissue.…”

“…In addition, interrogating ctDNA before or after surgery may provide a predictive tool for risk of recurrence. 11,12 There are also disadvantages to ctDNA as compared to tissue. For instance, ctDNA is found in only small amounts in the bloodstream, making it difficult to detect alterations.…”

Precision medicine in colorectal surgery: coming to a hospital near you

“…Utilizing this method, genetic abnormalities that underpin the emergence of clones resistant to therapy can be assessed over time. 7 In addition to monitoring response, ctDNA is being pursued as a prognostic marker to identify those at risk for tumour recurrence in early-stage CRC. 8 The ability to pre-identify patients with early disease that will not be cured by surgery alone has significant implications around eligibility for adjuvant therapy.…”