In an experimental metastasis model, DBM2 cells produce tumors in various tissues. (A) Clonal selection through experimental metastasis. The DBTRG-05MG cells were injected into the tail vein of athymic nude mice. Mice were sacrificed either when they became moribund (~12 weeks) or after 8 weeks. At necropsy, lung lesions were transplanted into nude mice subcutaneously. From these tumors, cells were harvested and injected into nude mice via tail vein. After the second cycle (M2) cells were expanded ex-vivo in culture. (B) DBTRG-05MG or DBM2 cells were injected via the tail vein into nude mice. After eight weeks mice inoculated with DBTRG-05MG cells had only a few pulmonary tumors (a, b). By contrast, lungs from mice bearing DBM2 cells were almost fully replaced with tumors (c, d), and metastatic foci were found in skeletal muscle (e), diaphragm (f), lymph nodes adjacent to the spinal cord (g) and in the chest cavity (h). H&E staining of formalin fixed sections from lungs of DBTRG-05MG cells (i) or DBM2 cells (j) eight weeks after tail vein injection. Invasion of DBM2 tumors into skeletal muscle (left 2 arrows) induces bone resorption (right arrow) (k) and replaces nearly the entire lymph node (arrow) (l, insert at low magnification).