Markers predictive of response, resistance and relapse in colorectal cancer

Abstract

Response to neo-adjuvant chemo-radiotherapy (CRT) in locally advanced rectal cancer varies. Circulating tumour DNA (ctDNA) has emerged as a surrogate marker of the tumour genome. I hypothesised that ctDNA could be an early indicator of response to enable therapy adaptation. Therefore tumour tissue and blood samples were collected pre, mid, post CRT and post-surgery using a single centre translational research protocol. A tumour informed approach was used to design up to 3 droplet digital polymerase chain reaction (ddPCR) assays per patient, ctDNA status after CRT was associated with MRI tumour regression grade response. ctDNA persistence or detection post CRT was an indicator of poor prognosis. ctDNA detection following curative surgery could predict relapse or indicate minimal residual disease. As pre-analytical factors can affect ctDNA detection rates, I wrote a translational protocol to assess the feasibility of a tumour-informed, multi-centre approach for ctDNA analysis from 48 CRC patients without distant metastases at diagnosis. Using ddPCR, ctDNA was detectable in 67% (n=32/48) pre-surgery and 19% (n=9/48) post-surgery. Pre-surgery ctDNA detection rates increased with stage. All 5 patients that relapsed had detectable ctDNA post-surgery and at the time of confirmed relapse. Of the patients with no evidence of relapse, 39 (91%) had undetectable ctDNA post-surgery. ctDNA identified patients at risk of developing metastases during CRT or after surgery and could be used to tailor treatment from as early as mid CRT or guide adjuvant chemotherapy decisions post-surgery in an attempt to prevent the development of metastases. Development of metastases represents a major cause of mortality. Comparing tumour tissue from primary CRC and corresponding lung metastases may be informative to understand the metastatic process and identify novel therapeutic targets. In matched samples from 13 patients, analysis of the transcriptome showed that only 944 out of 19,374 genes analysed (4.9%) were differentially expressed between primary CRC and respective lung metastases. Genes that were upregulated in metastases compared to primary tumours were most likely to be involved in the immune response pathway. Consensus molecular subtype 4 in lung metastases emerged as a poor prognostic marker. Findings require confirmation in a larger cohort.