Somatic Mutation during Metastasis of a Mouse Fibrosarcoma Line Detected by DNA Fingerprint Analysis

Metastatic nodules were examined by DNA fingerprint analysis. The probes used, Pc‐1 and Pc‐2, detect mutations as shifts in bands of the minisatellite loci which are dispersed among chromosomes. Four clonal lines of a fibrosarcoma from an F(1) mouse (C57BL/Ka × C3H/He) were selected for various metastatic potentials upon inoculation into syngeneic mice. These four lines exhibited many extra bands resulting from recombination and/or DNA slippage, indicating accumulation of mutations during the successive passages in mice. One of the four, a 505 cell line which had been passaged extensively in vitro and consisted of a heterogenous population, was inoculated into thirteen syngeneic mice, and gave rise to six lung metastatic nodules in two mice. All the nodules showed band‐patterns distinct from one another, although nodules within a given mouse tended to show similar patterns. When a genetically tagged 505‐05‐01 clone was analyzed, three of nine metastatic nodules obtained also revealed new bands. These results strongly suggest that somatic mutations occur at a high frequency during metastasis, providing direct evidence of genetic instability of the tumor cells.