D6 Serum markers and liquid biopsy

Topic

Oncological serum markers are proteins, hormones, or fragments of genetic material released by tumor cells directly into the patient's bloodstream.

These markers allow for the assessment of three distinct aspects of the tumor without the need for invasive procedures: the current number of tumor cells in the patient, the rate at which those cells are proliferating, and the tumor's genotype—the latter being determined through a specific type of marker analysis known as "liquid biopsy."

Unlike imaging techniques—such as CT scans, MRI, or PET scans—which only detect the physical tumor mass, serum markers can reflect tumor activity at stages where imaging shows nothing: before the tumor mass becomes visible (as seen with micrometastases or minimal residual disease), and following seemingly successful treatment, when marker levels rise again before the tumor mass reappears—a phenomenon known as biochemical recurrence.

Among all oncological serum markers, the liquid biopsy—which relies on tumor genetic material circulating freely in the blood—has been the most revolutionary development of the last decade; it enables the direct reading of the tumor's genotype, including driver mutations and emerging resistance mutations, from a simple blood sample, eliminating the need for a tissue biopsy.

Because it derives from genetic material released into the bloodstream by the entire tumor—rather than just a specific area—the liquid biopsy captures the clonal heterogeneity of the whole tumor, something a tissue biopsy cannot achieve, as the latter only reveals the specific site where the sample was taken. Furthermore, since it does not require an invasive procedure, liquid biopsy allows for repeated monitoring of the tumor's molecular profile throughout the course of treatment—something that, collectively, oncological serum markers make possible: turning the patient's blood into a dynamic window into the tumor, accessible at any stage of treatment.

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