<p>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).</p>