Efficacy of ATRA in treating the RARα2-overexpressing MM tumors in SCID mice. Mice (n = 5 in each group) were challenged with 2 × 10⁶ OCI-MY5 (OCI), EV, or RARα2 (R2)–transfected cells. At 10 days following tumor inoculation, ATRA treatment was given to EV-transfected (EV-OCI + ATRA) and R2-transfected (R2-OCI + ATRA) MM tumors 3 times per week for 3 weeks; OCI tumors receiving PBS (OCI + PBS) were used as controls. (A) Tumor volumes of mice following tumor injection. Results are expressed as means plus SD. (B) Survival curve of mice following tumor injection. Shown are the representative results of 2 independent experiments.