Spread of rectal cancer within veins. Histologic features and clinical significance.

Histologic evidence of venous invasion was demonstrated in 52 percent of 703 cases of rectal carcinoma. Quantitation of venous invasion and follow-up study showed that invasion of extramural veins was associated with a low 5 year survival rate (33 percent), whereas invasion limited to intramural veins was not. Spread into thick-walled extramural veins carries a very poor prognosis (15 of 91 patients survived 5 years). The corrected 5 year survival rate for stage C patients with invasion of thick-walled extramural veins was only 8 percent. Host reactions in and around the walls of invaded veins increase the survival rate; inflammatory damage to the vein walls and endarteritis obliterans are particularly important in this respect.