Macrophages in primary and secondary tumor growth: some implications for cancer therapy

Although it has been convincingly demonstrated that, under in vitro conditions, macrophages manifest an impressive cytolytic potential against a wide array of tumor cells, their role in the control of primary and secondary tumor growth in vivo has proved much more difficult to assess. In the present work, the evidence for the presence, efficient operation and modulation of host antitumor resistance and for a role for mononuclear phagocytes is briefly discussed and exemplified utilizing data derived from an experimental tumor model, the D-12 rat fibrosarcoma, in which macrophages appear to constitute a critical factor.