Stereoscopic observation via an implanted sight glass in mice bearing transplanted methylcholanthrene-induced A-cells showed tumorivascular hemorrhage at 1–2 h after tumor necrosis factor (TNF) administration, congestion at 4–6 h, and hemorrhage, congestion, and blood circulation blockage at 24 h.

Histological examination after TNF administration to mice bearing similar methylcholanethrene-induced A-cell transplants showed thrombus formation in the tumor vasculature at 4 h and thereafter. Suppression of this thrombus formation with heparin had no apparent influence on the necrotic response, tumor growth inhibition or complete cure rate following TNF administration to mice bearing the methylcholanethrene-induced A-cell tumors. The results suggest that direct toxicity of TNF on tumor vasculature is a factor in the overall antitumor mechanism of TNF.