Growth stimulation of tumor cells in diffusion chambers implanted in mice bearing chemically induced tumors

The growth of target tumor cells in diffusion chambers implanted subcutaneously into normal mice and into mice bearing chemically‐induced tumor was studied. It was observed that target‐cell multiplication was heavier in mice bearing a tumor less than 20 mm in diameter than in normal mice. In contrast, there was no growth difference between normal mice and mice bearing tumors with a diameter superior to 20 mm. This effect was observed when the target cells were of the same origin as the tumor borne by the mice. When the origin of tumors was different, the multiplication of target cells was stimulated but to a lesser degree. This phenomenon was observed in three out of four tested tumors. If the mice were irradiated with 500 R before tumor grafting and implantation of the diffusion chamber, the stimulation was still fully observable. In contrast, implanting the diffusion chambers intraperitoneally instead of subcutaneously or, alternatively, subcutaneously but far from the tumor, suppressed the stimulation. Also, no stimulation was observed if the grafted tumor was irradiated lethally or if a local inflammation was created by injection of bentonite or Freund's adjuvant. Tumor excision just before implantation of the chamber suppressed the stimulatory effect. Since the diffusion chambers are impermeable to cellular penetration it is concluded that the interstitial fluid of some tumor‐bearing mice contains diffusible factors capable of stimulating the multiplication of tumor target cells, close to the tumor.