An important regulator of gene expression during growth and development, and in neoplasms. tretinoin, also known as retinoic acid and derived from maternal vitamin a, is essential for normal GROWTH; and embryonic development. An excess of tretinoin can be teratogenic. It is used in the treatment of psoriasis; acne vulgaris; and several other skin diseases. It has also been approved for use in promyelocytic leukemia (leukemia, promyelocytic, acute).