The molecular profiling of solid tumors by liquid biopsy: a position paper of the AIOM-SIAPEC-IAP-SIBioC-SIC-SIF Italian Scientific Societies

Abstract

The term liquid biopsy (LB) refers to the use of various biological fluids as a surrogate for neoplastic tissue to achieve information for diagnostic, prognostic and predictive purposes. In the current clinical practice, LB is used for the identification of driver mutations in circulating tumor DNA derived from both tumor tissue and circulating neoplastic cells. As suggested by a growing body of evidence, however, there are several clinical settings where biological samples other than tissue could be used in the routine practice to identify potentially predictive biomarkers of either response or resistance to targeted treatments. New applications are emerging as useful clinical tools, and other blood derivatives, such as circulating tumor cells, circulating tumor RNA, microRNAs, platelets, extracellular vesicles, as well as other biofluids such as urine and cerebrospinal fluid, may be adopted in the near future. Despite the evident advantages compared with tissue biopsy, LB still presents some limitations due to both biological and technological issues. In this context, the absence of harmonized procedures corresponds to an unmet clinical need, ultimately affecting the rapid implementation of LB in clinical practice. In this position paper, based on experts' opinions, the AIOM-SIAPEC-IAP-SIBIOC-SIF Italian Scientific Societies critically discuss the most relevant technical issues of LB, the current and emerging evidences, with the aim to optimizing the applications of LB in the clinical setting.

Keywords: cfDNA; circulating cell-free DNA; circulating tumor DNA; ctDNA; digital PCR; liquid biopsy; next-generation sequencing; real-time PCR.

Figure 1

Technical and analytical aspects for liquid biopsy. cfDNA, cell-free DNA; ddPCR, droplet digital PCR; dPCR, digital PCR; NGS, next-generation sequencing.

Figure 2

Flow diagram algorithm depicting the role of ctDNA analysis in treatment-naive advanced NSCLC patients. ctDNA, circulating tumor DNA; EGFR, epidermal growth factor receptor; NSCLC, non-small-cell lung cancer. ^aEGFR exon 18 point mutation, exon 19 deletions, exon 20-21 point mutations; BRAF V600 point mutations. ^bALK, ROS-1, RET, and NTRK rearrangements; MET amplification and exon 14 skipping mutation, HER-2 amplification and point mutation; KRAS G12C point mutation (next-generation sequencing is preferred).

Figure 3

Flow diagram algorithm describing the role of ctDNA analysis in advanced oncogene-addicted NSCLC patients progressing during first-line TKIs. ALK, anaplastic lymphoma kinase; CT, platinum-based chemotherapy; ctDNA, circulating tumor DNA; EGFR, epidermal growth factor receptor; NGS, next-generation sequencing; NSCLC, non-small-cell lung cancer; PD, progressive disease; TKI, tyrosine kinase inhibitors. ^a Currently not approved by the Italian Medicines Agency: use only within a clinical trial or extended access program. ^bEGFR secondary mutations, MET or HER-2 alterations, ALK point mutations, PI3K or RAS/MAPK alterations, new genomic rearrangements.

Figure 4

Emerging applications of LB in breast cancer. AI, aromatase inhibitors; CDK4/6I, cyclin-dependent kinase 4/6 inhibitors; ctDNA, circulating tumor DNA; PFS, progression-free survival; PIK3CA, phospho-inositide 3-kinase. ^a Analysis of the following mutations: p.C420R, p.E542K, p.E545A, p.E545D, p.E545G, p.E545K, p.Q546E, p.Q546R, p.H1047L, p.H1047R, p.H1047Y.

Figure 5

Future perspectives in the clinical applications of liquid biopsy in patients with colorectal cancer. ctDNA, circulating tumor DNA. ^a RAS and BRAF mutational status: carried out either on primitive tumors or liver metastases. Discordance rate of 25%: primary tumor versus lymph node and lung metastases. ^b Optional.