Liquid Biopsy: The New Era of Cancer Detection and Diagnosis

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What is Liquid biopsy??

It is a technique for analyzing blood and other bodily fluids, for diagnosing and monitoring diseases. 
Because we don't need an invasive procedure, such as surgery, to obtain biofluids, liquid biopsies are non-invasive and painless. 
This feature of liquid biopsy makes it useful, when tissue biopsy cannot be used.  An important example of such applications is cancer, where liquid biopsy can be used as a diagnostic and monitoring tool.






How is Liquid Biopsy performed?

Liquid biopsy analyses can be done on blood as well as other bodily fluids such as urine, saliva or sputum. But, blood samples are the most commonly used samples for testing. A small amount of blood is drawn using a needle and syringe. Cells are separated from the blood and circulating DNA or RNA is extracted from the cell-free blood, or blood components such as plasma or serum. Levels of nucleic acids are commonly measured using techniques such as PCR. Changes in the sequence of nucleic acids called as mutations are analysed using PCR or next-generation sequencing.

The Advantages of Liquid Biopsies over Solid tumor biopsies...

For diseases such as cancer, initial analyses to identify the type of the tumor is done by tumor tissue biopsy. It also provides details of the genetic profile of the tumour. This helps in predicting whether the disease may progress and how it may respond to therapies. But tumor biopsies have many limitations:
A biopsy is usually taken from a part of a tumor. But, different parts of a primary tumour may show different genetic profiles - each portion may have acquired different mutations. So, the biopsy may not show all the mutations that are present in the tumor. In fact, if we compare a tumor with its metastases (tumor cells that have migrated to and formed a new tumor in a different organ), we may find that the genetic profile of the metastasis  is different from the primary tumor. So, mutations in some parts of the tumor may be missed in a tissue biopsy
Tumor tissue analysis needs a certain amount of tumor cells to be present to obtain accurate results. This may sometimes need multiple sampling if enough tumor cells are not present. Also, to study the tumor evolution over time or to assess the response to treatment, it is necessary to perform multiple serial biopsies at different time periods. 
In some cases, the tumor may not be present in an accessible area, making it difficult to obtain a tissue sample for further analyses. Tissue biopsies are often costly and invasive, and cause discomfort to the patient which makes multiple or serial biopsies impractical. 
Liquid Biopsy allows screening for disease through a simple blood test. It is minimally invasive and painless. In addition, since DNA released by cells from primary tumor, metastatic tumor as well as normal tissues are present, a liquid biopsy provides complete picture of the tumour genetic profile.
Since liquid biopsy is minimally invasive, it allows for repeated sampling. This, in turn, enables several applications such as real time monitoring of tumor genetic evolution. It can also be used to identify disease recurrence as well as disease progression. Similarly, it can indicate if a specific treatment is applicable to a patient, and if that treatment will reduce the risk of recurrence or progression. In addition, it allows for monitoring a patient's response to treatment.

Limitations of Liquid biopsy

Although liquid biopsy has various advantages, it also has many challenges when it comes to using it as a routine clinical test. 
Firstly, there is a lack of consensus among technical approaches to liquid biopsy. Because of this, liquid biopsy is not widely used within the medical community. More validation in clinical trials is required on the value of liquid biopsies in the medical setting to support the clinical utility of the test.
Then, there are limitations in test sensitivity. Given that circulating tumor cells or cell-free DNA are relatively rare compared to the number of normal cells or molecules in a blood sample, there are challenges to the test's ability to detect the cell-free DNA or circulating tumor cell. Low amounts of tumor cells or DNA in blood means that these tests require significantly greater technical efforts and expertise to obtain reliable results.
Because of these reasons, liquid biopsy is not yet considered as a standard testing procedure. Tissue biopsy still remains the gold standard for diagnosing diseases and for determining the characteristics of the disease. At present, liquid biopsy is not used as a replacement for the tissue biopsy test but used primarily as a complementary test to tissue biopsy.

Conclusion

In recent years, liquid biopsy has been recognized as a promising diagnostic technique for cancer and for other diseases. It is non-invasive and painless, can be used to measure treatment outcomes as well. This has great potential to improve patient care.  The technology is still in its infancy, and many challenges lie ahead, including ensuring that accurate results are obtained and maintaining the required standards of quality. Nonetheless, it is an evolving field with ongoing research showing its clinical potential. As the technology develops, there are a number of areas in oncology that could see a significant impact, including early detection, monitoring, and the optimization of treatment.

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