Early and late stages of foreign‐body carcinogenesis can be induced by implants of different shapes

Implanted foreign bodies of certain shapes, especially large non‐perforated polymer films, induce subcutaneous sarcomas in a high percentage of mice and rats; in contrast, implants of other shapes, e.g. , perforated or minced films or Millipore filters with 0.45 μm pores, are non‐carcinogenic or only weakly carcinogenic. Experiments described in this report have shown that when carcinogenic non‐perforated film was removed at 3.5 months after implantation and one of the “non‐carcinogenic” foreign bodies listed above was implanted into the same subcutaneous sites, a high percentage of sarcomas was induced. The same non‐carcinogenic or weakly carcinogenic foreign bodies implanted in the mice after total body γ irradiation or after single injection of ethylnitrosourea induced subcutaneous sarcomas in significantly higher percentages of animals than the same foreign bodies implanted in control mice. Our data suggest that foreign bodies of “non‐carcinogenic” or “weakly carcinogenic” shapes can act as efficient promoters of subcutaneous carcinogenesis initiated by other agents such as implanted “carcinogenic” foreign bodies, ionizing radiation or chemical carcinogen.