Enhancement of the incidence of metastasis in tumor-resected mice. Influence of soluble tumor extract and splenectomy.

The M3 mammary tumor was transplantable in syngeneic BALB/c mice, and metastasized spontaneously into the lungs. When primary tumors were resected in early stages of evolution (10 days), the number of mice with lung metastasis decreased. When specific soluble tumor extracts, tumor cell culture supernatant or formalinized tumor cells were inoculated 2 and 4 days after surgery, an enhancement of lung metastasis was observed. When splenectomy was performed at the time of tumor resection, this enhancement was abrogated. These results suggest that tumor plasma cell membranes or the products released by them play an important role in dormant metastases growth, but only in the presence of the spleen, suggesting its involvement in the mechanism of the metastatic process.