Vaccination in multiple sites increases antitumor efficacy. CEA-Tg mice were implanted with 1 × 106 Panc02.CEA cells s.c. on day 0 and vaccinated in 0, 1, 2, 4, or 6 sites with 1 YU yeast-CEA/site starting on day 7, then weekly for the duration of the experiment. Tumor volume was measured twice a week and recorded. A, no treatment (n = 10). B, 1YU in 1 site (n = 9). C, 1 YU in 2 sites (n = 10). D, 1 YU in 4 sites (n = 10). E, 1 YU in 6 sites (n = 10). Bars indicate average tumor volume ± SD. Open squares, no treatment. Closed circles, yeast-CEA.