Circulating tumour cell enumeration, biomarker analyses, and kinetics in patients with colorectal cancer and other GI malignancies.

Objective: Most of the work in terms of liquid biopsies in patients with solid tumors is focused on circulating tumor DNA (ctDNA). Our aim was to evaluate the feasibility of using circulating tumor cells (CTCs) in peripheral blood samples from patients with advanced or metastatic gastrointestinal (GI) cancers. Methods: In this prospective study, blood samples were collected from each patient in 2 AccuCyte® blood collection tubes and each tube underwent CTC analysis performed utilizing the RareCyte® platform. The results from both tubes were averaged and a total of 150 draws were done, with 281 unique reported results. The cadence of sampling was based on convenience sampling and piggybacked onto days of actual clinical follow-ups and treatment visits. The CTC results were correlated with patient- and tumor-related variables. Results: Data from a total of 59 unique patients were included in this study. Patients had a median age of 58 years, with males representing 69% of the study population. More than 57% had received treatment prior to taking blood samples. The type of GI malignancy varied, with more than half the patients having colorectal cancer (CRC, 54%) followed by esophageal/gastric cancer (17%). The least common cancer was cholangiocarcinoma (9%). The greatest number of CTCs were found in patients with colorectal cancer (Mean: 15.8 per 7.5 ml; Median: 7.5 per 7.5 ml). In comparison, patients with pancreatic cancer (PC) had considerably fewer CTCs (Mean: 4.2 per 7.5 ml; Median: 3 per 7.5 ml). Additionally, we found that patients receiving treatment had significantly fewer CTCs than patients who were not receiving treatment (Median 2.7 versus 0.7). CTC numbers showed noteworthy disparities between patients with responding/stable disease in comparison to those with untreated/progressive disease (Median of 2.7 versus 0). When CTCs were present, biomarker analyses of the four markers human epidermal growth factor receptor 2 (HER2)/programmed death-ligand 1 (PD-L1)/Kiel 67 (Ki-67)/epidermal growth factor receptor (EGFR) was feasible. Single cell sequencing confirmed the tumor of origin. Conclusion: Our study is one of the first prospective real-time studies evaluating CTCs in patients with GI malignancies. While ctDNA-based analyses are more common in clinical trials and practice, CTC analysis provides complementary information from a liquid biopsy perspective that is of value and worthy of continued research.

False-Positive Liquid Biopsy Assays Secondary to Overlapping Aberrant Methylation from Non-Cancer Disease States.

Introduction: Liquid biopsies are increasingly being adopted in the care of patients with cancer. Not only in patients with metastatic disease but the utility is also being recognized in earlier phases of the journey of a patient with cancer. More recently, methylated platforms are offering another lens of looking at the same question more so in minimal residual disease (MRD) and early detection settings. While false positives secondary to clonal hematopoiesis of indeterminate potential (CHIP) are recognized as one entity to consider when interpreting these assays, and advanced CHIP filtering bioinformatics platforms can prevent this, false positives secondary to aberrant methylation are not described. Case Presentation: Herein, we report a case of a patient with hepatitis C-related viremia and a very high viral load that had a false-positive plasma-only colorectal MRD assay. The colorectal MRD assay spontaneously cleared on hepatitis C virus therapy which led to clearance of the virus. Conclusion: As these assays are increasingly applied in real-world settings, it would be of value to consider non-cancer chronic disease states that may lead to aberrant methylation that could lead to a false-positive assay.

Larotrectinib in Mismatch-Repair-Deficient TRK Fusion-Positive Metastatic Colon Cancer After Progression on Immunotherapy.

A 43-year-old woman presented with recurrent metastatic colon cancer with metastases to the peritoneum after having initially been diagnosed with stage IIB colon cancer and deferring adjuvant chemotherapy. Circulating tumor DNA (ctDNA)-based liquid biopsy testing revealed microsatellite instability-high (MSI-H) status, which was also confirmed on tissue testing. This patient then underwent four cycles of pembrolizumab and two cycles of ipilimumab and nivolumab (CTLA-4 rescue) with, unfortunately, progression of the disease. The patient was subsequently treated with larotrectinib, given the findings of TRK fusion-positive cancer on next-generation sequencing (NGS), and she was able to undergo curative surgery two months later that showed complete pathologic response. She continues to have no evidence of disease years later as well as no detectable ctDNA on NGS as well as tumor-informed minimal residual disease platforms. This case represents a marked and durable response to larotrectinib in a patient with deficiency in mismatch repair/MSI-H metastatic colorectal cancer harboring an NTRK fusion, bringing to light the potential for use of larotrectinib in earlier treatment lines in patients, and/or choice of targeted therapy versus immunotherapy in this patient subset.