Liquid biopsy is most relevant for patients who already have a confirmed or suspected cancer diagnosis, particularly solid tumours such as lung, breast, colorectal, and prostate cancer. It is not currently a general cancer screening test for people without any cancer diagnosis or symptoms, though this use is being actively researched.

It is most useful in situations such as:

*When a tissue biopsy is not possible or too risky, for example if the tumour is in a hard-to-reach location or the patient’s health does not allow for a surgical procedure
*When there is not enough tissue material left from a previous biopsy to run additional genetic tests
*When a patient’s cancer has progressed on treatment and doctors need to check for new resistance mutations before choosing the next therapy
*When doctors want to monitor how well a patient is responding to treatment over time, through repeated blood draws
*When checking for early signs of cancer recurrence after treatment has ended