|Year : 2020 | Volume
| Issue : 1 | Page : 20-22
Emerging role of liquid biopsy in the practice of precision oncology
Department of Medical Oncology, HCG Cancer centre, Bengaluru, India
|Date of Web Publication||22-Oct-2020|
Dr. G K Babu
Department of Medical Oncology, HCG Cancer Centre, Bengaluru
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Babu G K. Emerging role of liquid biopsy in the practice of precision oncology. J Precis Oncol 2020;1:20-2
The cornerstone of treatment in oncology rests on the correct diagnosis. This is primarily based on the interpretation of pathology in the tissues involved. The tissue is obtained by a biospy in solid tumours and from blood or bone marrow in hematological cancers. The therapy in oncology, be it surgery, radiotherapy or systemic therapy has undergone a sea of change from being emperic to becoming very precise.
The advances in molecular biology has led to a better undertanding of cancer biology and pathway systems. This has led to ever increasing cure rates in many cancers and maintaining good quality of life when cure is a remote possibility. Even in mestastic disease, our treatment strageries have kept patients living longer. With each progression we are able to study the recurrance mechanisms and use therapies that precisely target these pathways. For a longtime the tissue for analysis at progression was an invasive procedure of biopsy. But now this answer can be obtained by resorting to liquid biopsy.
Liquid bospy is especially useful when the recurrent tumour is not accesable for several reasons. Liquid Biopsy can involve the study of circulating tumour cells (CTC's) or circulating nucleic acids( Ct DNA or Ct RNA ) or exosomes. The work on CTC's in contrast to Ct DNA is slow and limited due to the more complex nature of protocols for CTC's.
Liquid biopsies can use blood, serum or body fluids including but not limited to urine, saliva, sputum etc. The analysis from a small biospy of a large tumour has an inherent draw back of overlooking the hetrogeneity of the tumour while the liquid biospy takes this into account ! It also allows for real time, serial sampling.
The National Cancer Institute (NCI) defines liquid biospy as,“ a test done on a sample of blood to look for cancer cells from a tumour that are circulating in blood≵ (1). Liquid biopsy can also assess cell free micro RNA (miRNA) and non -coding RNA (ncRNA), Extracellular vesicles including exosomes and microvesicles, tumour educated platelets. All these can aid as biomarkers, response to therapy and also understand the biology and evolution of tumours.
Cristofannilli et al correlated the enumerated CTC's with outcomes in breast cancer patients (2) studies of Cohen in colon cancer (3) and de Bono in prosate cancer (4) showed good coorelation between CTC's and outcomes. Zhang et al published a meta analysis of 6815 breast cancer patients from 49 studies again demonstarting a coorelation of CTC's with progression free survival (PFS) and overall survival (OS) (5)
As mentioned earlier work with CTC's has several problems and hence data with CTC is still limited in contrast to work with circulating nucleic acids especially Ct DNA. It has progressed very rapidly due to the relative ease of working protocols. The growth has also been accelerated by the ever falling costs of genomic analysis. The Human Genome project has analysed data from several cancers, that is in public domain has also played a significant part.
There are several methods to study nucleic acids including real time polymerase chain reaction (PCR), digital droplet PCR, BEAMing and Next genration sequencing (NGS). All these platforms have their share of advantages and disadvantages and one needs to choose based on their research questions. NGS is one of the most sensitive and widely used platforms today.
Our group has been working on culturing CTC'S and looking at the cluster formation in agar micro-wells. The CTC clusters were charaterized as loose, tight and very tight clusters based on the compactness, using DAPI stain and its flourescence intensity (Fig 1).
The cluster charaterization was done on day 7 and day 14 of therapy and after every 3 cycles of treatment and more if required . We studied two cohorts, a metastatic non small cell lung cancer (NSCLC) and a metastatic breast cancer one. We found that the tightness of the CTC cluster correlated with responses to therapy and could even be correlated with continuing response or development of resistance to ongoing treatment (Fig 2 & 3).
Although the cohorts are small we were able to show survival coorelation with cluster characteristics (Fig 4). This was true for chemotherapy based andalso for targeted therapies (6). The amount of published data with Ct DNA is tremendous, especially in Lung cancer. In fact NSCLC is considered the poster boy of liquid biopsy today.
In the present day practice, the standard protocol has molecular analysis of NSCLC tumours at diagnosis. This is because nearly 60% of these tumours harbor driver mutations that are targetable. The commonest is Epidermal growth factor receptor (EGFR) mutations. This is seen in 20-35% of Indian population. The other druggable pathways are ALK, ROS, Her-2, Met, Ret, PDL1, NTRK and many more.
In case a patient has an activating EGFR mutation, the treatment of choice is pill, a tyrosine kinase inhibitor (TKI), and we now have three generations of these. Once a patient is on a first generation TKI the response is seen in nearly everyone. The response typically lasts for an year. Once there is a disease progression, we resort to repeating the lung biopsy or any other site of progression to understand the resistance mechanisms. In nearly 70% it is as a result of a mutation, categorised as T790 M.
A rebiopsy is many times not feasible due to a variety of reasons. Here is when liquid biopsy has a potential role. Ct DNA analysis have shown to correlate very well with tissue analysis to pick up the resistance mutation and plan further treatment. Goto et al were one of the first to demonstrate this coorelation while treating patients with geftinib (7). Oxnard et al showed that the T790M mutations demonstrated in the tissue and from Ct DNA had similar outcomes on treatment with osemertinib (8). Studies are underway to quantitate T 790 M mutation load and use it to monitor treatment akin to the use of BCR-ABL quantification in chronic myeloid leukemia.
These mutation analyses are now being tested in saliva and urine, which are even less invasive than blood sampling. Mutation analysis with deep NGS can help pick up many mutations for which repurposing of drugs would be possible. Thompson et al studied a cohort of 102 NSCLC patients and demonsatrated that Ct DNA analysis was in 86 and 56 of them could have benefit from off- label drugs (9).
Our study of Ct DNA of 45 adenocarcinoma and 15 squamous non small cell lung cancer showed that EGFR mutations were seen even in squamous small cell cancers (10). Ct DNA has also been exploited in treatment of breast cancer. Ben O'Leary at ASCO 2017, presented Ct DNA assessement to predict sensitivity to palbociclib and fulvestrant. The SOLAR – 1 study in breast cancer demonstarted that P13K mutation could be used as a biomarker for uses of alpelisib (11).
Recently, the researchers of Johns Hopkins University published results about their blood test “cancerSEEK”. They looked for certain proteins in blood to prove the presence of cancer. Lichtenfeld, the Deputy Chief Medical Officer of the American Cancer Society, says that “cancer's early detection by means other than Xrays, colonoscopies, or Pap smears has been subject of research for at least 2 decades, now we have been learning about ctDNA to evaluate cancer and about pros and cons of trying to find cancer early.
The benefits of early detection are several, but we have learned the lessons of leadbias from conventional screening procedures. Furthermore, the lessons from detecting elevated PSA, we know that many people die with prostate cancer rather than because of it.
Similar is the story of elevated CA125. Thus as in screening, we have a lot to learn about the optimal use of liquid biopsy. Venkatesan et al. in the ASCO 2016 Education Book have discussed tumour evolutionary principles and have shown the role of studying ctDNA for the same.
Single CTC profiling is an emerging, existing concept that has adopted extremely sensitive technologies to its full. The analysis of Ct DNA and single cell profiling could help understand tumour heterogeneity in a better way than we know today (12). Liu MC at al, recently published evidence to show that Ct DNA can be anlysed to detect nearly 50 cancers with a specificity of 93% even when the patients were asymptomatic .
We are now working on testing drug sensitivity on cultured CTC's. This could open a new era in drug development and practice of oncology. To conclude, liquid biopsy as a concept has made tremendous inroads into the daily practice of oncology today and it will emerge to continue to do so in the various domains of oncology – in the way we adopt it to treat our patients, understand resistance mechanisms and understand the biology of cancer in a better way.
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