Elena Castellanos-Rizaldos

Liquid biopsy for cancer screening, patient stratification and monitoring

Molecular characterization of a patient’s tumor to guide treatment decisions is increasingly being applied in clinical care and can have a significant impact on disease outcome. These molecular analyses, including mutation characterization, are typically performed on tissue acquired through a biopsy at diagnosis. However, tumors are highly heterogeneous and sampling in its entirety is challenging. Furthermore, tumors evolve over time and can alter their molecular genotype, making clinical decisions based on historical biopsy data suboptimal. Personalized medicine for cancer patients aims to tailor the best treatment options for the individual at diagnosis and during treatment. To fully enable personalized medicine it is desirable to have an easily accessible, minimally invasive way to determine and follow the molecular makeup of a patient’s tumor longitudinally. One such approach is through a liquid biopsy, where the genetic makeup of the tumor can be assessed through a biofluid sample. Liquid biopsies have the potential to help clinicians screen for disease, stratify patients to the best treatment and monitor treatment response and resistance mechanisms in the tumor. A liquid biopsy can be used for molecular characterization of the tumor and its non-invasive nature allows repeat sampling to monitor genetic changes over time without the need for a tissue biopsy. This review will summarize three approaches in the liquid biopsy field: circulating tumor cells (CTCs), cell free DNA (cfDNA) and exosomes. We also outline some of the analytical challenges encountered using liquid biopsy techniques to detect rare mutations in a background of wild-type sequences.

Improved EGFR mutation detection using combined exosomal RNA and circulating tumor DNA in NSCLC patient plasma

Abstract Background A major limitation of circulating tumor DNA (ctDNA) for somatic mutation detection has been the low level of ctDNA found in a subset of cancer patients. We investigated whether using a combined isolation of exosomal RNA (exoRNA) and cell-free DNA (cfDNA) could improve blood-based liquid biopsy for EGFR mutation detection in non-small-cell lung cancer (NSCLC) patients. Patients and methods Matched pretreatment tumor and plasma were collected from 84 patients enrolled in TIGER-X (NCT01526928), a phase 1/2 study of rociletinib in mutant EGFR NSCLC patients. The combined isolated exoRNA and cfDNA (exoNA) was analyzed blinded for mutations using a targeted next-generation sequencing panel (EXO1000) and compared with existing data from the same samples using analysis of ctDNA by BEAMing. Results For exoNA, the sensitivity was 98% for detection of activating EGFR mutations and 90% for EGFR T790M. The corresponding sensitivities for ctDNA by BEAMing were 82% for activating mutations and 84% for T790M. In a subgroup of patients with intrathoracic metastatic disease (M0/M1a; n = 21), the sensitivity increased from 26% to 74% for activating mutations (P = 0.003) and from 19% to 31% for T790M (P = 0.5) when using exoNA for detection. Conclusions Combining exoRNA and ctDNA increased the sensitivity for EGFR mutation detection in plasma, with the largest improvement seen in the subgroup of M0/M1a disease patients known to have low levels of ctDNA and poses challenges for mutation detection on ctDNA alone. Clinical Trials NCT01526928

Exosome-Based Detection of EGFR T790M in Plasma from Non–Small Cell Lung Cancer Patients

Purpose: About 60% of non–small cell lung cancer (NSCLC) patients develop resistance to targeted epidermal growth factor receptor (EGFR) inhibitor therapy through the EGFR T790M mutation. Patients with this mutation respond well to third-generation tyrosine kinase inhibitors, but obtaining a tissue biopsy to confirm the mutation poses risks and is often not feasible. Liquid biopsies using circulating free tumor DNA (cfDNA) have emerged as a noninvasive option to detect the mutation; however, sensitivity is low as many patients have too few detectable copies in circulation. Here, we have developed and validated a novel test that overcomes the limited abundance of the mutation by simultaneously capturing and interrogating exosomal RNA/DNA and cfDNA (exoNA) in a single step followed by a sensitive allele-specific qPCR. Experimental Design: ExoNA was extracted from the plasma of NSCLC patients with biopsy-confirmed T790M-positive (N = 102) and T790M-negative (N = 108) samples. The T790M mutation status was determined using an analytically validated allele-specific qPCR assay in a Clinical Laboratory Improvement Amendment laboratory. Results: Detection of the T790M mutation on exoNA achieved 92% sensitivity and 89% specificity using tumor biopsy results as gold standard. We also obtained high sensitivity (88%) in patients with intrathoracic disease (M0/M1a), for whom detection by liquid biopsy has been particularly challenging. Conclusions: The combination of exoRNA/DNA and cfDNA for T790M detection has higher sensitivity and specificity compared with historical cohorts using cfDNA alone. This could further help avoid unnecessary tumor biopsies for T790M mutation testing. Clin Cancer Res; 24(12); 2944–50. ©2018 AACR.