RARA and breast cancer: We hypothesize that ATRA induces autophagy only in breast cancer cells that are not terminally differentiated and can be differentiated by retinoids for the following reasons: (1) selective activation of RARα by AM580 or ATRA is sufficient to induce both autophagy and cytodifferentiation20 in SKBR3 cells, and (2) MDA-MB453 cells are resistant to ATRA-dependent autophagy and differentiation.