A new liver-tumor model in the rat.

A new tumor model for testing and comparing the effect of different forms of treatment on liver tumors is described. Single tumors were induced in the liver of rats by the implantation of small pieces taken from a subcutaneously growing tumor. Tumor growth was determined by measuring the weight of the implanted tumors after the animals had been killed. In this way, weight curves for treated and untreated tumors could be defined. The weight of untreated liver tumors increased exponentially with time (tumor weight in milligrams = 1 + e(t-0.31)/5). In addition, tumor growth defined as the geometric mean of three perpendicular diameters was determined. Tumor-diameter curves showed a linear increase with time in the untreated groups (tumor diameter in millimeters = 0.4 t + 1.90). The model was tested by assessing the effect of intraperitoneally injected cisplatin. The dose chosen produced a marked delay in tumor growth. On the basis of the weight gain shown by the treated animals and tumor growth delay, a therapeutic index can be defined, thus enabling to compare quantitatively different forms of treatment according to their antitumor effect and toxicity.