Numerical evaluation of the kidney invasion test.

We have implanted MO4 transformed mouse cells attached to a collagen matrix (artificial tumor) under the renal capsule of syngeneic mice. It was our purpose to evaluate whether or not the kidney invasion test (KIT) could be used for the determination in vivo of the invasive capacity of cultured cell populations. Invasion was expressed in terms of the proportion of the depth of the invasive part of the tumor to the total tumor thickness (invasion rate), both measured macroscopically after hemisection of the kidney. Macroscopic findings were confirmed by histology. For MO4 cells the invasion index changed in function of time after implantation. The relationship 'invasion index versus time after implantation' was demonstrated to be constant in 3 independent groups of mice. Therefore, we propose determination of the invasion rate versus time in the KIT as a method to compare the invasive capacity in vivo of different cell lines.