“Oxygen Effect” and Tumor Size as Related to Response of C3H/Ba Adenocarcinoma to Local X Irradiation

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Abstract
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 an 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 percent O2 under 2 atmospheres of pressure instead of air at 1 atmosphere of pressure, results with the small (7–10 mm.) 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.