The expression levels of C1q, C3/C3a, C5/C5a and the regulatory protein clusterin were upregulated in HCC, and this upregulation is responsible for aggressive tumour phenotypes, including tumourigenesis, metastasis, stemness and immune suppression, indicating the potential of these molecules as biomarkers and therapeutic targets for HCC. The gene discussed is C5AR1; the disease is neoplasm.