Effect of splenectomy on the progression of postoperative pulmonary metastases of the 3LL tumor.

Surgical excision of the local intrafootpad tumor of the 3LL lung carcinoma is followed by accelerated growth of its lung metastases. When, however, splenectomy was performed concomitantly with tumor excision, the acceleration of lung metastases was prevented. In cases where excision of the local tumor took place when it reached large sizes, concomitant splenectomy did not prevent the accelerated growth of the lung metastases. If, however, at these stages of tumor growth splenectomy was performed 3 days prior to the excision of the tumor, it did prevent the accelerated growth of metastases. Intrafootpad reinoculation of tumor cells following tumor excision and splenectomy caused further reduction in metastatic growth. The results suggest that existence of two possible distinct mechanisms which control metastatic growth: the local tumor might exert non-immunologically, an inhibitory effect on its lung metastases, and the spleen, possibly via suppressor lymphocytes, may suppress an immune effector activity against the tumor metastases, an activity which is manifested following splenectomy.