Effect of all‐trans retinoic acid on induction, lethality and immunogenicity of murine methylcholanthrene‐induced fibrosarcomas

The effect of 200 μg doses of all‐trans retinoic acid, given over a long duration (daily for 8 weeks, suspended for 3 weeks, then resumed daily for 4 weeks) or short duration (daily for 30 days), on the induction of fibrosarcomas in C57BL/6J mice by MCA was evaluated. A reduced level of carcinogenesis was observed with both lengths of retinoic acid treatment, since respective incidences of MCA fibrosarcomas were 63 and 61% of those in saline‐treated controls. In other studies, the effect of all‐trans retinoic acid on syngeneic growth of two experimental fibrosarcomas (B6 25 and B6 27, induced previously in C57BL/6J mice by MCA) was assessed. Retinoic‐acid‐treated mice were more resistant to higher doses of viable B6 27 (LD50 = 2.85) and especially B6 25 (LD50 = 3.80) than were corresponding saline‐ or corn‐oil‐treated controls (LD50