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).