Since ALDH1A1 generates two different RAs – the widely known all-trans retinoic acid (ATRA) and the lesser known 9-cis retinoic acid (9CRA) – and our previous work on myeloma pointed to ATRA as an important signaling ligand [39], this research concentrated initially on ATRA. The gene discussed is ALDH1A1; the disease is plasma cell myeloma.