This dichotomy has even been observed in cells of the same tissue origin: decreased PKCα expression mediates all-trans retinoic acid (ATRA)-induced inhibition of G1 → S progression in SKRB-3 breast cancer cells (Nakagawa et al., 2003), whereas PKCα is required for ATRA-induced growth arrest in T-47D breast cancer cells (Cho et al., 1997). The gene discussed is PRKCA; the disease is breast cancer.