Temporal morphologic changes in human colorectal carcinomas following xenografting

The temporal morphologic changes of human colorectal carcinomas following xenografting into immunosuppressed mice were investigated by the use of light and transmission electron microscopy. The results show that colorectal carcinomas undergo a series of morphologic changes during the initial 30-day period following transplantation. During the initial 1-5-day period the majority of tumor cells die, and during the following 5-10-day period the necrotic debris created during the 1-5-day period is removed by host-supplied inflammatory cells. Only small groups of peripherally placed tumor cells survived at the end of the first 10 days. During the 10-20-day period the tumor cell populations of xenografts were reestablished by a morphologically heterogeneous population of tumor cells, and during the 20-30 day period consolidation of this process continued and some xenografts showed macroscopic evidence of growth. The authors hypothesize that human colorectal carcinomas, like the antecedent epithelium, contain subpopulations of undifferentiated cells that give rise to populations of more-differentiated cells.