Liquid biopsy: How a simple blood test can change cancer detection?

Over the last couple of decades, cancer has become arguably the most pressing health concern in India. According to ICMR-National Cancer Registry Programme estimates, India recorded about 15.69 lakh new cancer cases in 2025, and the instances have only increased since then. The biggest concern, however, is not just the rising number of cases but also the delayed diagnosis. When cancer is diagnosed early, treatment is often more effective, less intensive, and has better chances of long-term control.

“Advanced-stage cancers, on the other hand, may require more advanced treatments, and even then, the prognoses may not be as promising. This is why early detection remains one of the most important priorities in cancer care, which brings us to liquid biopsy – a recent advancement in cancer diagnostics, which has the potential to improve cancer detection, treatment selection and disease monitoring,” Dr Vineet Talwar, Medical Oncologist at Rajiv Gandhi Cancer Institute and Research Centre (RGCIRC) in New Delhi, tells Health Shots.

Liquid biopsy could be a game-changer

Traditionally, cancer diagnosis has relied largely on imaging, pathological tests, and tissue biopsy, in which a small tumour sample is taken and studied under a microscope or through molecular tests. A liquid biopsy, on the other hand, usually involves testing a blood sample, although other body fluids such as cerebrospinal fluid (CSF), urine, pleural fluid, and saliva may also be tested for cancer-related signals. These may include circulating tumour DNA, circulating tumour cells, cell-free RNA, tumour-derived proteins or other biomarkers released by cancer cells into the bloodstream.

Liquid biopsy is a major development

Liquid biopsy is seen as an important advancement in cancer treatment for three reasons:

1. Minimally invasive

Unlike a traditional tissue biopsy, which may require a surgical or image-guided procedure, a liquid biopsy usually needs only a blood sample. Blood can be drawn within minutes, without surgery or anaesthesia, making it easier for patients who are elderly, weak, medically unfit for invasive procedures, or have tumours in difficult-to-reach locations.

2. Repeatability

Since it relies on a simple blood draw, a liquid biopsy can be repeated at different stages of treatment. This helps oncologists monitor how the tumour is responding to treatment, detect emerging resistance, and make timely treatment decisions, rather than relying solely on scans that are typically repeated at longer intervals.

3. Broader tumour insight

A single-tissue biopsy studies cancer cells from a single selected tumour site. Liquid biopsy may capture genetic material shed into the blood from different tumour areas and, in some cases, from metastatic sites. This can offer a wider view of the cancer’s molecular profile and help guide more personalised treatment planning.

Liquid biopsy is already changing cancer care

Liquid biopsy is not a promise for the future. In several cancers, it is already being used to support diagnosis, treatment selection, and disease monitoring, especially when tissue samples are limited or repeated tissue biopsies are difficult to obtain.

Here’s an overview of some of the current applications:

1. Lung cancer: In advanced disease, a liquid biopsy can help identify key genetic alterations, such as EGFR mutations, that guide targeted therapy. This is particularly useful when there is insufficient tumour tissue for molecular testing, or when obtaining another tissue sample may be difficult for the patient. It can also help detect resistance mutations during treatment, allowing doctors to consider changing therapy sooner.
2. Colorectal cancer: After surgery for colorectal cancer, CTDNA testing can help detect minimal residual disease, which means microscopic cancer cells that may remain in the body but cannot be seen on imaging.
3. Breast cancer: In selected breast cancer cases, liquid biopsy is being studied and used to detect residual disease, monitor recurrence risk and understand tumour evolution during treatment. It may also help identify genetic changes that influence treatment choices, particularly in advanced or metastatic disease, where repeated tissue biopsy may not be practical.
4. Other solid tumours: Liquid biopsy is also being explored and used in several other solid cancers, including prostate, ovarian, and melanoma, to track tumour behaviour over time. For patients already on treatment, regular blood draws may reveal emerging resistance mutations before clear progression appears on scans.

This can help oncologists respond faster and personalise treatment decisions more effectively.

What are the benefits of liquid biopsies?

While liquid biopsies have many benefits and applications, they are not a replacement for standard cancer screening or tissue biopsy at present. Tests such as mammography for breast cancer, Pap smear and HPV testing for cervical cancer, colonoscopy or stool-based tests for colorectal cancer, and low-dose CT in selected high-risk individuals for lung cancer continue to play an important role.

Similarly, when cancer is suspected, a tissue biopsy often remains necessary to confirm the diagnosis, determine the cancer type, and guide treatment. However, liquid biopsies certainly represent a key advancement in cancer diagnosis, making cancer detection more accessible, less invasive and more precise. In contrast, for oncologists, it represents an important step towards more biomarker-driven, personalised and regulated cancer care.