Cancer causes approximately 10 million deaths annually across the globe [1]. The maximum number of cancer deaths in 2020 were caused by the following solid cancers—lung, colorectal, liver, stomach and breast in that decreasing order. Targeted therapy or Precision Medicine in cancer has made a huge impact in the management of cancer. For adopting the practice of Precision Medicine, it is imperative that precise targets be identified in the evolving landscape of cancer mutations.
The traditional methods of post treatment follow up are by performing biopsy of a suspected recurrence site which is an invasive process, leading to patient anxiety, in addition to being more resource intensive. It is also a more expensive procedure and requires adequate skill for correct interpretation.
Traditional biopsy also has the limitation of not giving an idea of all the clones present in the tumour due to sampling bias and complex tumour heterogenity however, liquid biopsy circumvents this issue and gives a snapshot of the entire clonal milleu of the tumour.
From 1948 when Mandel first detected cell free DNA (cfDNA), has come a long way, albeit gradually [2]. Fetal DNA from maternal plasma could be detected in 1997 by Lo et al. [3]. Fifteen years from then, The American College of Obstetricians & Gynaecologists recommended non invasive prenatal screening in 2012. Epidermal growth Factor Receptor (EGFR) mutations in liquid biopsy in non small cell lung cancer from plasma was FDA approved in 2016. By 2020, FDA had approved testing of multiple mutations from plasma of solid tumours using NGS.
Circulating tumour DNA (Ct DNA) can be detected from body fluids other than plasma & serum, like stool, urine, saliva, cerebro spinal fluid, pleural and peritoneal fluid. Ct DNA, is released into blood when malignant cells undergo apoptosis or necrosis. Detection of ct DNA from plasma is an excellent non invasive tool for monitoring disease recurrence and minimal residual disease detection. Cancer cells are known to acquire secondary resistance to chemotherapeutic drugs. Sequential sampling of ctDNA for the detection of evolving mutations during the course of therapy which confer resistance to chemotherapeutic drugs is another application of liquid biopsy.
Detection of mutations in KRAS gene in Colorectal cancer from ct DNA gives important clues to not initiate therapy with Cetuximab or Panatimubab. Timely detection of druggable mutations like EGFR T790M which can be detected in ctDNA during the course of therapy dictates that Osmeritinib should be initiated [4].
Since ctDNA is present in minute quantities in patient plasma, it is recommended that detection of MRD or mutations from ctDNA should employ technologies with low limit of quantitation like Next Generation Sequencing (NGS) or digital droplet PCR (ddPCR). Ct DNA is present in normal population to the tune of 10 ng/mL. Since, the limit of quantitation in these platforms are very low, commercial assays offer a sensitivity of 1/1000 for SNPs. With such precise and accurate detetction of mutations from a sea of cf DNA akin to finding needle from a hay stack, clinicians will have lead time to modify the course of treatment.
The ctDNA ride, however, does charter into choppy waters, issues of false positivity continue to remain an issue as is the case with all assays with very high sensitivity. Half life of cfDNA is very less hence preanalytics have to be very robust. Sese et al. have proposed that ct DNA in Streck tubes are stable for five days at room temperature [5]. The prohibitive cost of Streck tubes is a barrier hence samples collected in EDTA tubes processed and stored within two hours are a viable option. The clearance of fetal DNA from maternal serum is one hour and complete clearance from maternal blood occurs in two days.
With the cost of NGS getting more competitive and the fact that ddPCR sensitivity can match upto NGS, liquid biopsy is going to be as ubiquitous an assay as a run of the mill tumour marker in the times to come [4]. With massive bisulphite sequencing being adopted for pan cancer screening since it is more sensitive than whole genome sequencing ctDNA atlases are going to be the future databases for cancer screening. Liquid biopsy therefore paves the road ahead for precision medicine by providing druggable targets rapidly.
Footnotes
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References
- 1.Ferlay J, Ervik M, Lam F, Colombet M, Mery L, Piñeros M et al. Global cancer observatory: cancer today. Lyon: International Agency for Research on Cancer; 2020. https://gco.iarc.fr/today. Accessed Feb 2021.
- 2.Mandel P, Metais P. Les acides nucleiques du plasma sanguine chez l’ home. CR Seances Soc Biol Fil. 1948;142:241–243. [PubMed] [Google Scholar]
- 3.Lo YM, Corbetta N, Chamberlain PF, Rai V, Sargent IL, Redman CW, et al. Presence of fetal DNA in maternal plasma and serum. Lancet. 1997;350(9076):485–487. doi: 10.1016/S0140-6736(97)02174-0. [DOI] [PubMed] [Google Scholar]
- 4.Papadimitrakopoulou VA, Han JY, Ahn MJ, Ramalingam SS, Delmonte A, Hsia TC. Epidermal growth factor receptor mutation analysis in tissue and plasma from the AURA3 trial: osimertinib versus platinum—pemetrexed for T790M mutation -positive advanced non-small cell lung cancer. Cancer. 2020;126(2):373–380. doi: 10.1002/cncr.32503. [DOI] [PubMed] [Google Scholar]
- 5.Sese M, Somoza R, Maestu I, Ureste MM, Sanchez AS, et al. Validation of cell free DNA collection tubes for determination of EGFR mutation status in Liquid biopsy from NSCLC patients. Oncol Ther. 2019;7:131–139. doi: 10.1007/s40487-019-00099-9. [DOI] [PMC free article] [PubMed] [Google Scholar]