Immunodeficiency and cancer: mechanisms involved.

This is a short overview concerning possible relationships between immunodeficiency and cancerogenesis/leukemogenesis. Following introductory remarks on concomitant and sinecomitant antitumor immunity, various factors/mechanisms that could influence tumor-host-interactions are discussed, in particular properties of neoplastic cell lines, the microenvironment, cellular components of nonspecific resistance, and specific, i.e. antigen-directed, cell-mediated and humoral immune responses against cancer cells. The increased incidence of malignant neoplastic processes in patients with inherited or acquired immunodeficiency raises the question if a lack of antitumoral defense or ineffective antiviral immunity is more important. Available data indicate that once a cancer has reached a certain size, the chances for the host to reject it solely with the help of its immune apparatus are minimal. The possibility remains that immune reactions may be more efficacious against small numbers of immunogenic tumor cells, i.e. in the very earliest phase of a neoplastic process and when the cancer begins to metastasize.