Treatment of the mouse Lewis tumor by the association of radiotherapy and immunotherapy with Bacillus Calmette-Guérin.

Three groups of 6 to 8-week-old male mice with transplanted C57BL/6 X DBA/2F1 tumor were irradiated by a single dose of 60Co localized on the tumor in association with i.p. injections of lyophilized Bacillus Calmette-Guérin. When the animals were sacrificed, tumor parameters (weight, surface area, and volume) were determined. Lung metastases were counted using a binocular magnifying glass. When Bacillus Calmette-Guérin injections were begun the day after the irradiation, tumor growth and the number of lung metastases were significantly decreased in comparison with the control group (p less than 0.01). However, there was no significant difference between the control group, which received radiotherapy alone, and the groups in which Bacillus Calmette-Guérin treatment was started after the 4th day postirradiation. This emphasizes the importance of timing in combined radioimmunological treatment.