Regional differences in the growth of tumor cells injected intraperitoneally into syngeneic adult mice.

C755 mammary carcinoma cells were injected i.p. into adult mice of the strain of origin (C57BL/6). By using a common insertion point but directing the needle caudad or craniad, a differential delivery of tumor cells was deliberately achieved. At high cell doses, the median survival time was shorter for animals receiving anterior injections than for those given pos terior injections. At limiting cell doses, an inoculum sufficient to achieve 50% lethality for anteriorly directed cells led to only 20% mortality in the posteriorly injected group. Analysis of distribution and retention of tumor cells following inoculation indicated that cells injected caudad tended to adhere to the peritoneal lining posteriorly more than anteriorly while, con versely, cells injected craniad tended to remain lodged ante riorly more than posteriorly. The experiments were repeated using Sarcoma 180 cells of two types: tumors grown as solid tumors; and tumors adapted to ascites form. When Sarcoma 180 cells derived from a solid tumor were injected i.p., they showed an even more striking anterior-posterior differential. In contrast, animals injected with ascites-derived Sarcoma 180 cells showed no such differential effect. These results extend the earlier observations that tumors inoculated intradermally or s.c. into various parts of the trunk skin show striking anterior-posterior differentials in growth. The experiments suggest that solid tumor-derived cells inoculated i.p. also manifest this regionally determined response corre lated with their differential lodging in the anterior and posterior peritoneal lining. From a practical standpoint, it is at once apparent that the precise location of a cell inoculation must be controlled and recorded and that scientific error may result from the assumption that all i.p. injections are necessarily similar. From a biological standpoint, it seems of paramount importance to determine what basic underlying physiological factors of the organism can cause such marked and general effects on tumor growth, but investigations to date have not led to any clear explanation for the basis for the regional differ ences observed in the growth of inoculated tumor cells.