Metastatic inefficiency: intravascular and intraperitoneal implantation of cancer cells

The term metastatic inefficiency reflects the fact that most of the cancer cells entering the metastatic process are killed; some of the evidence for this is reviewed in the case of renal and colorectal carcinomas. Although much emphasis has been placed on the rapid intravascular death of cancer cells during hematogenous metastasis, much less is known about the inefficiency associated with peritoneal carcinomatosis, and up to the present no systematic and direct numerical studies have been reported of the relative metastatic inefficiencies associated with seeding of cancer cells by intraperitoneal, vascular, and lymphatic routes. However, studies on people and laboratory animals indicate that most of the cancer cells released into the peritoneal cavity are killed. Some of the mechanisms involved in killing constitute part of cellular defense operating through the release of toxic free radicals. One of these, hydrogen peroxide, given by intraperitoneal injection, has been shown to retard the development of malignant ascites in mice previously given intraperitoneal injections of cancer cells. It is suggested that local irrigation with hydrogen peroxide during surgery for abdominal tumors may be effective in inhibiting the development of peritoneal carcinomatosis.