“…More recently, such tests have been extended to include syngeneic tumour-bearing animals, challenged intravenously (IV) (Vaage, 1973; Proctor et al, 1973a;Milas et al, 1974;Proctor et al, 1974), and such studies have demonstrated that specific immunological factors may influence metastatic spread. Further support for this concept is provided by reports of increased spontaneous blood-borne metastatic spread, following immunosuppressive procedures in syngeneic animal models (Fisher et al, 1969; Proctor et al, 1973a), and either an increase or a decrease in such spread following specific active immunotherapeutic measures (Vanwijk et al, 1971 ;Godrick et al, 1972; Proctor et al, 19736).However, as has been emphasized recently by Weiss et al (1974), relatively little attention has been paid to the influence of specific immune anti-turnour mechanisms on the initial localization and fate of blood-borne tumour cells in the target organ, prior to the establishment of metastases. These authors demonstrated that a high proportion of radiolabelled tumour cells was localized in the lungs of normal, tumour-bearing and hyperimmune mice 1 h after injection and that there was significantly less radioactivity in the lungs of the tumour-bearing and hyperimmune animals than in those of normal controls.…”