title: An immune reaction may be necessary for cancer development.
abstract: BACKGROUND
  The hypothesis of immunosurveillance suggests that new neoplasms arise very frequently, but most are destroyed almost at their inception by an immune response. Its correctness has been debated for many years. In its support, it has been shown that the incidences of many tumor types, though apparently not all, tend to be increased in immunodeficient animals or humans, but this observation does not end the debate.
  There is an alternative to the surveillance hypothesis; numerous studies have shown that the effect of an immune reaction on a tumor is biphasic. For each tumor, there is some quantitatively low level of immune reaction that, relative to no reaction, is facilitating, perhaps even necessary for the tumor's growth in vivo. The optimum level of this facilitating reaction may often be less than the level of immunity that the tumor might engender in a normal subject.
  
  
  CONCLUSIONS
  The failure of a tumor to grow as well in the normal as it does in the immunosuppressed host is probably not caused by a lack of tumor-cell killing in the suppressed host. Instead, the higher level of immune response in a normal animal, even if it does not rise to tumor-inhibitory levels, probably gives less positive support to tumor growth. This seems more than a semantic distinction.
authors.forename: Richmond T
authors.initials: RT
authors.lastname: Prehn
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000633:toxicity; D005260:Female; D006801:Humans; D007121:Immunocompetence; D016867:Immunocompromised Host; D008325:Mammary Neoplasms, Experimental / Q000276:immunology; D008324:Mammary Tumor Virus, Mouse / Q000472:pathogenicity; D008748:Methylcholanthrene / Q000633:toxicity; D051379:Mice; D008819:Mice, Nude; D016513:Mice, SCID; D018448:Models, Immunological; D009368:Neoplasm Transplantation / Q000276:immunology; D009369:Neoplasms / Q000209:etiology* / Q000276:immunology*; D009374:Neoplasms, Experimental / Q000139:chemically induced / Q000276:immunology; D012192:Retroviridae Infections / Q000276:immunology; D014185:Transplantation, Isogeneic; D014412:Tumor Virus Infections / Q000276:immunology
chemical_list: D002273:Carcinogens; D008748:Methylcholanthrene