The complement system represents a pillar of the innate immune response. This system,
critical for host defense against pathogens, encompasses more than 50 soluble, and
membrane-bound proteins. Emerging evidence underscores its clinical relevance in
tumor progression and its role in metastasis, one of the hallmarks of cancer. The multistep
process of metastasis entails the acquisition of advantageous functions required for
the formation of secondary tumors. Thus, targeting components of the complement
system could impact not only on tumor initiation but also on several crucial steps
along tumor dissemination. This novel vulnerability could be concomitantly exploited
with current strategies overcoming tumor-mediated immunosuppression to provide a
substantial clinical benefit in the treatment of metastatic disease. In this review, we
offer a tour d’horizon on recent advances in this area and their prospective potential
for cancer treatment