The utility of ctDNA in colorectal cancer with peritoneal metastases

Overview: Challenges of Treating Peritoneal Surface Malignancies

Peritoneal surface malignancies (PSM) includes an expansive disease spectrum, ranging from low-grade appendiceal mucinous neoplasm to metastatic processes from invasive adenocarcinomas of the gastrointestinal tract. Management of PSM faces numerous challenges, from diagnosis to delivery of care, both from a treatment and navigational standpoint. This article outlines the various hurdles faced at different branch points and current management recommendations.

LncRNA PCAT6 is a predictor of poor prognosis of colorectal cancer

BACKGROUND

The long non-coding RNA (lncRNA) prostate cancer-associated transcript 6 (PCAT6) has been studied in many cancers, yet its relationship with colorectal cancer (CRC) remains poorly defined. Here, we conducted an analysis of The Cancer Genome Atlas (TCGA) database to better clarify the role of PCAT6 in this cancer type.

METHODS

Wilcoxon rank-sum tests were utilized to assess relative levels of PCAT6 in CRC tumors and normal tissues, while logistic regression analyses were utilized to compare the relationships between PCAT6 levels and clinicopathological findings. Kaplan-Meier curves and Cox regression analyses were used to gauge correlations between PCAT6 and patient survival outcomes, while the biological roles of this lncRNA were investigated via a gene set enrichment analysis (GSEA) approach. The expression level of PCAT6 in CRC cell lines was detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR).

RESULTS

PCAT6 levels were significantly correlated with CRC patient lymph node metastasis (N) stage [odds ratio (OR) =1.8 for N1 & N2 vs. N0], lymphatic invasion [OR =1.9 for yes vs. no), distant metastasis (M stage) (OR =2.1 for M1 vs. M0), carcinoembryonic antigen (CEA) level (OR =1.9 for >5 vs. ≤5), perineural invasion (OR =1.9 for yes vs. no), pathologic stage (OR =1.9 for stage III/IV vs. stage I/II), and neoplasm type (OR =2.1 for rectal adenocarcinoma vs. colon adenocarcinoma) (all P<0.05). CRC patients expressing higher PCAT6 levels exhibited poorer survival outcomes than those expressing low levels of this lncRNA (P=0.017), and in univariate analyses, higher PCAT6 levels were linked to worse overall survival [hazard ratio (HR) =1.540; 95% confidence interval (CI): 1.079-2.199; P=0.017], with this relationship also being preserved in a multivariate analysis (HR =6.892; 95% CI: 1.713-27.727, P=0.007). GSEA revealed high PCAT6 expression to be linked to differential DNA methylation enrichment, with high PCAT6 levels being associated with changes in base excision repair, cellular senescence, G2/M DNA damage checkpoint, chromatin-modifying enzyme, and gene silencing by RNA activity. The high expression of lncRNA PCAT6 in CRC cell lines was demonstrated by PCR experiments.

CONCLUSIONS

PCAT6 represents a promising prognostic biomarker of poor CRC patient survival outcomes, with DNA methylation and RNA-mediated gene silencing being potentially promising mechanistic pathways whereby this lncRNA may shape patient outcomes.

Circulating Tumor DNA and Management of Colorectal Cancer

Although the incidence of colorectal cancer (CRC) has decreased as a result of increased screening and awareness, it still remains a major cause of cancer-related death. Additionally, early detection of CRC recurrence by conventional means such as CT, endoscopy, and CEA has not translated into an improvement in survival. Liquid biopsies, such as the detection circulating tumor DNA (ctDNA), have been investigated as a biomarker for patients with CRC in terms of prognosis and recurrence, as well as their use to guide therapy. In this manuscript, we provide an overview of ctDNA as well as its utility in providing prognostic information, using it to guide therapy, and monitoring for recurrence in patients with CRC. In addition, we discuss the influence the site of disease may have on the ability to detect ctDNA in patients with metastatic CRC.

Clinical application of circulating tumour DNA in colorectal cancer

Liquid biopsies that detect circulating tumour DNA (ctDNA) have the potential to revolutionise the personalised management of colorectal cancer. For patients with early-stage disease, emerging clinical applications include the assessment of molecular residual disease after surgery, the monitoring of adjuvant chemotherapy efficacy, and early detection of recurrence during surveillance. In the advanced disease setting, data highlight the potential of ctDNA levels as a prognostic marker and as an early indicator of treatment response. ctDNA assessment can complement standard tissue-based testing for molecular characterisation, with the added ability to monitor emerging mutations under the selective pressure of targeted therapy. Here we provide an overview of the evidence supporting the use of ctDNA in colorectal cancer, the studies underway to address some of the outstanding questions, and the barriers to widespread clinical uptake.