"OXYGEN EFFECT" AND TUMOR SIZE AS RELATED TO RESPONSE OF C3H/Ba ADENOCARCINOMA TO LOCAL X IRRADIATION

The C3H/Ba mammary adenocarcinoma transplanted into the thigh muscle of the C3H/He mouse, the inbred strain of mice in which the tumor originated, was studied by irradiation in vivo with am opposed pair of 250 kv x-ray beams. Tumors 7 to 10 mm in diameter were lethally damaged by 5500 r in greater numbers than tumors 10 to 15 mm in diameter. When the treatment was given while the animals breathed 100 per oent O/sub 2/ under 2 atmospheres of pressure instead of air at 1 atmosphere of pressure, results with the small tumors indicated that the increased oxygen tension slightly enhanced the cure rate; tumors 10 to 15 mm in diameter did not show a greater cure rate if the therapy were given under increased oxygen tension. The data show that there is a rapid and progressive anemia (decrease in hematocrit) with growth of the tumor. (auth)