Fig. 5.

A graph illustrates the growth-inhibitory effect of ATRA in vivo. SYO-1 (5 × 10⁶) cells suspended in 100 mL phosphate-buffered saline were subcutaneously injected into the hind flank of male BALB/c nu/nu athymic mice. Mice were randomly assigned to ATRA-treated (●), vehicle-treated (■), and untreated (▴) groups (five mice per group). ATRA treatment (20 mg/kg) was started on Day 2, and tumor volume was measured on Days 3, 7, 10, 14, and 17. In vivo treatment with ATRA achieved growth-inhibitor effect at Day 17 (*p = 0.026 versus vehicle; **p = 0.034 versus no treatment). The inhibitory effect, however, was not complete, and the tumor started to regrow with the same kinetics as pretreated cells.