Harnessing complement biomarkers for precision cancer care

The tumor microenvironment (TME) consists of various immune and non-immune cells, along with proteins from different origins, and plays a crucial role in tumor development, treatment response, and patient prognosis. Complement system is a key player in the TME. It is a proteolytic cascade that generates cleavage fragments capable to activate cells through specific receptors or deposit on cells and tissues. This review summarizes current data on the complement system as a potential biomarker in cancer. Transcriptomic analyses have classified tumors based on the impact of complement gene expression on prognosis. Immunostaining provides insights into the expression and deposition of complement proteins and fragments in tumors and TME cells. In body fluids such as blood, measuring complement activation fragments and detecting anti-complement autoantibodies have identified non-invasive biomarkers relevant to certain cancer types. With the rise of complement-targeting therapies and new tools for analyzing the complement system in tumors and body fluids, it is time to define its role in cancer management. This includes its potential for cancer detection, staging, and potentially for treatment monitoring.