Studies on blood vessels in experimental tumors Part II. Influence of anti-cancer agent on tumor vessels

The following results were obtained by serial investigation of tumor vessels in a transparent chamber in rat skin: 1) Normal vessels and tumor vessels tended to be disturbed by the administration of bleomycin. Cyclophosphamide therapy begun at an early stage of tumor when the vascular supply was copious resulted in improvement of the irregular pattern and size variation of vessels. Moreover, the central tumor mass regressed. Chemotherapy applied at an advanced stage of tumor when the circulation was sluggish and scatterd tumor necrosis was present did not cause any tumor regression. Moreover, tumor necrosis increased. 3) Prolongation of survival in tumor-bearing rats and tumor regression due to cyclophosphamide were significantly enhanced by the additional use of high pressure oxygen with the drug. Microscopic observation of tumor vessels in vivo indicated that this combination therapy produced favorable conditions in the tumor microcirculatory system. These results clarify the relationship between tumor microcirculation and tumor growth, as well as the therapeutic effects of anti-cancer agents.