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Induction of macroscopic metastases via surgery. The site of the primary tumor inoculum is critical.

Primary subcutaneous inoculation of fibrosarcoma cells into syngeneic rats leads to progressive local tumor growth. In this experimental model, the incidence of macroscopic metastases is critically dependent on the site of the primary tumor implant. Inoculation of tumor cells into the back is only exceptionally followed by macroscopic metastases; in sharp contrast, inoculation of tumor cells into the thigh gives rise to spontaneous metastatic tumor growth in a high proportion of the animals. Surgical intervention involving excision of the primary tumor either gives frequently rise to macroscopic metastases (when the primary tumor was inoculated in the back) or markedly enhances the growth of metastatic foci (when the primary tumor was inoculated in the thigh).