A panel of 42 breast cancer cell lines was challenged with increasing concentrations of ATRA (11 nM-10 μM) for 3, 6, and 9 days, and cell growth was determined.The graphs show the growth-inhibitory effect exerted by the indicated concentrations of ATRA in SKBR3, HCC-1954, and MDA-MB436 cells which are representative of lines characterized by a high, intermediate and low ATRA score, respectively. Each point is the mean ± SD of three replicate cultures. **Significantly lower than the corresponding vehicle-treated group (P-value < 0.01, Student's t-test). 