Cell fusion is a natural process in normal development and tissue regeneration. Fusion between cancer cells and macrophages generates metastatic hybrids with genetic and phenotypic characteristics from both maternal cells.
Monocytes are actively recruited to the tumor stroma and polarized by anti-inflammatory molecules to an immunosuppressive phenotype, so called Tumor Associated Macrophages, TAMs. High infiltration of TAMs is correlated to poor prognosis in breast, prostatic, ovarian and cervical carcinoma.
The cell fusion theory provides an explanation to several aspects regarding cancer, including the origin and metastasis of tumor cells.