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Since its inception, liquid biopsy has seen much development and applications in cancer diagnostics. The technique can revolutionise early detection and diagnosis of cancer and monitor disease progression and therapeutic response. In this chapter, we will explore the critical applications of liquid biopsy and delve into some of the alternative novel applications where it is having an impact.

Early Detection of Cancer

One of the most significant benefits of early cancer detection is that it is easier to treat and reduces patient suffering. Most crucially, it increases survival rates. Whilst Invasive tumour biopsies remain the primary method of diagnosis in solid cancers, a liquid biopsy can address the limitations of these approaches, including difficulties in accessing certain tumours and changes in tumour genetic composition. Cancer Research UK introduced its Early Detection and Diagnosis of Cancer Roadmap in 2022, which outlines how the early detection and diagnosis ecosystem can improve accurate cancer detection at an early stage.

Monitoring Disease Progression and Therapeutic Response

Cancer progression and patient response to therapy are two critical factors that impact the overall prognosis of a cancer patient. Liquid biopsy is a crucial diagnostic tool and is invaluable when it comes to monitoring these two factors. This innovative approach provides real-time information about tumours and their changes by analysing the blood’s circulating tumour DNA (ctDNA).

The benefits of liquid biopsy go beyond just monitoring the progression of cancer. It also allows doctors to evaluate the effectiveness of therapy and determine the prognostic significance of ctDNA in a patient’s response to treatment. In several cancer types, such as lung, ovarian, and colorectal cancer, an elevated presence of ctDNA is often associated with a poor clinical outcome and an increased risk of tumour relapse.

In addition, liquid biopsy enables doctors to continuously monitor a tumour’s genotype, providing real-time information on changes that can help predict and prevent relapses. This insight allows patients and doctors to make quicker and more effective treatment decisions, leading to better outcomes.

Detection of Minimal Residual Disease

According to the Dissemination of circulating tumour cells at night: role of sleep or circadian rhythm, “Metastasis of a primary tumour to a secondary site is responsible for approximately 90% of all cancer-related deaths”. Analysing circulating tumour cells (CTCs) using liquid biopsy can reveal unique insights into metastasis and the types of primary tumours that can metastasise. In addition, research has shown that CTCs can travel as clusters or micro-emboli in the blood, with CTC clusters associated with a poorer prognosis than single CTCs.

Minimal residual disease (MRD) is a term used to describe cancer cells that persist in a patient’s body after treatment. Liquid biopsy tests can detect these residual cancer cells through liquid biopsy tests that detect circulating tumour cells (CTCs) or cell-free DNA (ctDNA) at low levels. This type of biopsy can be a valuable tool for detecting MRD in various kinds of cancer.

MRD can also occur due to tumour cells spreading from the primary tumour site to other parts of the body, even if there are no visible signs of metastasis. Early detection of MRD is crucial for patients with cancer, as it can allow for earlier intervention and treatment to prevent disease relapse. By monitoring CTCs and ctDNA levels during post-surgical follow-up assessments, Doctors can detect MRD many months before traditional radiological imaging methods detect them.

Conclusion

The many applications of liquid biopsy continue to revolutionise cancer diagnostics and hold great promise for the future. The technique offers a minimally invasive method for detecting cancer early, monitoring disease progression, and tracking therapeutic response. By understanding the biological processes underlying the release of circulating biomarkers, we can continue to improve the sensitivity and specificity of liquid biopsy tests and deliver real-time monitoring of constantly changing tumours.