Biologic determinants of tumor growth in healing wounds.

The morphologic characteristics of a scar may render it an "immunologically privileged site" providing fertile ground for tumor occurrence and growth. We sought to extend this concept and to determine the effect of different stages of wound healing on tumor occurrence. Syngeneic strain-2 guinea pigs and a methylcholanthrene-induced liposarcoma (MCA-2) were used. Incisional flank wounds were created at appropriate intervals such that at the time of tumor inoculation each group of animals had a sequentially aged wound which was a) acute, b) three weeks old, c) nine weeks old, d) 11 weeks old, e) created one week after tumor injection, or f) no wound. Wounds which were three, nine, or 11 weeks old consistently caused a significant increase in tumor growth rate following inoculation of a single cell tumor suspension (<.001). The delayed wounds, or those created following after tumor injection, and the acute wounds did not promote increased tumor growth. This study demonstrates that the ability of a wound to amplify or retard tumor growth may vary with its age. As a postulate we suggest that the relative paucity of lymphatic regeneration within scar tissue may render it an "immunologically privileged site" such that early recognition and destruction of tumor cells within the scar may be delayed long enough for the tumor to grow to a "critical size." Subsequent to this regardless of the host's immunocompetence the tumor can no longer be destroyed by an immune mechanism. The general lack of progressive growth of tumor cells placed in acute wounds suggests that they were not protected from immunocompetent cells and were destroyed by the ongoing inflammatory response to injury. Therefore, different biologic characteristics of a surgical scar are important in potentiating or retarding tumor growth. Variations in such factors may account for the local recurrence of cancer in operative wounds.